Using Compartmentalization to Mitigate the Impacts of Stack Effect in Tall Residential Buildings

Transcription

1 Using Compartmentalization to Mitigate the Impacts of Stack Effect in Tall Residential Buildings by Junting Li A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Department of Civil & Mineral Engineering University of Toronto Copyright by Junting Li 2018

2 Performance Analysis of Compartmentalization Strategy to Mitigate the Impacts of Stack Effect in Tall Residential Buildings Junting Li Master of Applied Science Department of Civil & Mineral Engineering University of Toronto 2018 Abstract Natural stack action affects all types of buildings, but it becomes a significant driving force and imposes adverse impacts on tall buildings. Traditional approaches such as corridor pressurization system, revolving doors, and airtight exterior envelope to mitigate stack-action induced problems may not be effective for tall residential buildings; hence, an alternative mitigation strategy is required. Compartmentalization is one potential solution which can be used to effectively control stack induced pressures and airflows. However, there exists little information in the academic literature about the effectiveness of using compartmentalization. This thesis begins by looking at the difficulties faced when assessing the effectiveness of compartmentalization. Then, using computer simulation, a quantitative analysis on the potential improvement resulting from implementing compartmentalization is presented. The simulation results showed that compartmentalization is an effective means of controlling contamination air movements, improving building serviceability, providing sufficient ventilation, and reducing the total energy consumption related to conditioning air. ii

3 Acknowledgements I would like to offer my gratitude to my thesis supervisors, Dr. Brenda McCabe and Dr. Kim Pressnail. Both of you have profoundly influenced me as a researcher with your knowledge, dedication, and positive outlook. Although there were times when I encountered uncertainties and challenges, both of you motivated and encouraged me to keep pursuing my goals. Moreover, I sincerely appreciate your help in my writings. Being a non-native speaker of English, with your assistance, I was able to sharpen my writing skills and to become a more effective communicator. Both of you have made the two-year master program the most memorable experience in my life. I would like to thank the team members of the Building Tall Research Centre at the University of Toronto. The sincere thanks to Hiba Ali, Yunting Chen, Patrick Marquis, Farid Mirahadi, Kamellia Shahi, Pouya Zangeneh, and Li Hao Zhang for your supports. Also, special thanks to Dr. Arash Shahi for your comments on my research project and the editing support. I would like to thank my family and friends for all your supports which motivated and encouraged me through the challenges. I would also like to acknowledge the help from RESCON for initiating and supporting this project, support from NSERC Research Grant CRDPJ , and Peter Adams of Morrison Hershfield for providing the detailed information with regard to the case study. iii

4 Table of Contents Acknowledgements... iii Table of Contents... iv List of Tables... ix List of Figures... xi List of Acronyms... xiii Chapter 1 Introduction Background Objectives Scope Methodology Organization of Thesis... 4 Chapter 2 Compartmentalization as a Solution to Managing Stack Effect in Tall Residential Buildings Abstract Stack Effect Problems Related to Stack Effect Stack Effect in Tall Buildings vs Low-rise Buildings Stack Effect in Residential Buildings vs Commercial Buildings Scope and Objectives Approaches to Mitigate Stack Induced Problems Active Strategies Mechanical Pressurization System Mechanical Ventilation in Elevator Shaft Space Passive Strategies Vertical Zoning Revolving Door and Vestibule Improving Exterior Envelope Airtightness Improving Interior Partitions Airtightness iv

5 Improving both Exterior and Interior Partitions Airtightness Compartmentalization Approaches to Implementing Compartmentalization Assessment of Compartmentalization in Tall Residential Buildings Limitations in Measuring Airtightness in Tall Residential Buildings Inconsistency in Testing Methods Whole Building Test Guarded Blower Door Test Suite/Floor Level Blower Door Test Inconsistency in Airtightness Metrics Air Change Rate Normalized Airflow Rate Leakage Area Inconsistency in Normalized Surface Area Calculation Conclusions Recommendations and Future Steps Chapter 3 Using a Modeling Approach to Evaluate the Effects of Compartmentalization on Stack Action in Tall Residential Buildings Abstract Introduction Stack Effect in Tall Residential Buildings Compartmentalization Effectiveness of Compartmentalization Objectives Methodology Nodal Analysis Network Research Methodology Calibration Assumptions in the model Data inputs used in calibration Calibration result v

6 3.6 Evaluation of Compartmentalization Strategies Assumptions in the Base Model Evaluation Metrics Compartmentalization Steps Result and Discussion Base Model: No Compartmentalization Airtightness Inputs Simulation Result Model SC1: Exterior Envelope Improvement Airtightness Inputs Simulation Result Model SC2: Suite Interior Improvement and HVAC Adjustments Airtightness Inputs HVAC Inputs Simulation Results Model FC1: Corridor Separation Improvement Airtightness Inputs Simulation Results Model FC2: Vestibule Installation and HVAC Adjustments Airtightness Inputs HVAC Inputs Simulation Results Compartmentalization Steps Summary Parking Garage Compartmentalization Approaches to Compartmentalizing Parking Garage Benefits of Compartmentalizing Parking Garage Conclusions Chapter 4 Full Compartmentalization Evaluation Compartmentalization steps Compartmentalization Steps Summary Chapter 5 Closing Chapter...66 vi

7 Chapter 6 References...71 Appendix A. Calibration Simulation Software: CONTAM93 and CONTAM Backdraft Damper HVAC System Data Selection Roof & Elevator Machine Room Garage & Garbage Chute Shaft Supply Vent on F1 & F Suite Calibration Process Calibration Result Appendix B. Evaluation Metrics Stairwell Door Suite Entrance Door Appendix C. Simulation Results...94 Appendix D. Details of Full Compartmentalization Steps Base Model: No Compartmentalization (mentioned in Section 3.7.1) Airtightness Inputs Simulation Result Model A: Exterior Envelope Improvement Airtightness Inputs Simulation Result Model B: Interlock Exhaust Damper (mentioned as Model SC1 in Section 3.7.2) Airtightness Inputs Simulation Result Model C: Suite Floor Slab Improvement Airtightness Inputs Simulation Results Model D: Suite Demising wall Improvement vii

8 9.5.1 Airtightness Inputs Simulation Results Model E: Suite Individual Ventilation (mentioned as Model SC2 in Section 3.7.3) HVAC Inputs Simulation Results Model F: Corridor Separation Improvement (mentioned as Model FC1 in Section 3.7.4) Airtightness Inputs Simulation Results Model G: Vestibule Installation Airtightness Inputs Simulation Results Model H: Corridor HVAC Adjustment (mentioned as Model FC2 in Section 3.7.5) HVAC Inputs Simulation Results viii

9 List of Tables Table 1. List of Previous Field Measurements on Airtightness of Existing MURBs Table 2. The Simulation Results after the Calibration Process Compared to the Field Measurements Table 3. Maximum Allowable Force and Pressure Difference across Different Doors Table 4. Computer Simulation Steps in Evaluating Compartmentalization Approaches Table 5. Airtightness Value of the Curtain Wall Façade from Previous Studies Table 6. Airtightness Inputs in Base Model Table 7. Simulation Results from Base Model Table 8. Airtightness Inputs in Model SC1: Improving Exterior Envelope Table 9. Simulation Results from Model SC1: Improving Exterior Envelope Table 10. Airtightness Inputs in Model SC2: Improving Suite Interior Partitions Table 11. HVAC Inputs in Model SC2: HVAC Adjustments Table 12. Simulation Results from Model SC2: Improving Suite Interior Walls and HVAC System Table 13. Airtightness Inputs in Model FC1: Improving Corridor Separations Table 14. Simulation Results from Model FC1: Improving Corridor Partitions Table 15. HVAC Inputs in Model FC2: Installing Vestibules and Increasing HVAC Airflow Rates Table 16. Simulation Results from Model FC2: Installing Vestibules Table 17. Computer Simulation Steps in Evaluating Compartmentalization Approaches Table 18. Field Measurement Results Collected with No Wind, HVAC System Operating, and All Doors Closed Table 19. Absolute Pressure of Various Location Calculated from the Measurement Data Table 20. Leakage Values of Doors from Field Tests and Literature Table 21. Airtightness of Building Components Used in the Calibrated Model and Suggested from the Literature Table 22. Sensitivity Analysis Results Table 23. Minimum Closing Force Provided by Door Closers Table 24. Simulation Results of Models in Chapter ix

10 Table 25. Simulation Results of Models in Section Table 26. Simulation Results of Models in Section Table 27. Airtightness Value of the Curtain Wall Façade from Previous Studies Table 28. Airtightness Inputs in Base Model Table 29. Simulation Results from Base Model Table 30. Airtightness Inputs in Model A: Improving Exterior Envelope Table 31. Simulation Results from Model A: Improving Exterior Envelope Table 32. Airtightness Inputs in Model B: Interlock Exhaust Damper Table 33. Simulation Results from Model B: Interlock Exhaust Damper Table 34. Airtightness Inputs in Model C: Improving Suite Floor Slab Table 35. Simulation Results from Model C: Improving Suite Floor Slab Table 36. Airtightness Inputs in Model D: Improving Suite Demising Walls Table 37. Simulation Results from Model D: Improving Suite Demising Walls Table 38. HVAC Inputs in Model E: Corridor HVAC Adjustment Table 39. Simulation Results from Model E: Suite Individual Ventilation Table 40. Airtightness Inputs in Model F: Improving Corridor Separations Table 41. Simulation Results from Model F: Improving Corridor Partitions Table 42. Simulation Results from Model G: Installing Vestibules Table 43. HVAC Inputs in Model H: Corridor HVAC Adjustment Table 44. Simulation Results from Model H: Corridor HVAC Adjustment x

11 List of Figures Figure 1. Diagram to Illustrate Stack Effect Driver... 7 Figure 2.Theoretical Pressure Differential due to Stack Effect Applied on Buildings (Adapted from Hutcheon & Handegord, 1994) Figure 3.Schematic Floor Plan Layout of Ground Floor Lobby (Left) and Typical Residential Floor (Right) Figure 4. Simulated Pressure Difference in Base Model Figure 5. Simulated Pressure Difference with Exterior Envelope Improvement (Model SC1) Figure 6. Simulated Pressure with Interior Airtightness Improvement (Model SC2) Figure 7. Simulated Pressure Difference with Corridor Separation Improvement (Model FC1). 52 Figure 8. Simulated Pressure with Corridor Vestibules (Model FC2) Figure 9. Compartmentalization Steps: A Summary of the Model Responses Figure 10. A Summary of Total Ambient Air Entering the Building from All Compartmentalization Steps Figure 11. A Summary of Building Performance from All Compartmentalization Steps Compared the Results from Compartmentalizing Parking Garage Figure 12. A Summary of Building Performance from All Compartmentalization Steps Figure 13. A Summary of Total Ambient Air Entering the Building from All Compartmentalization Steps Figure 14. Calibration Process Figure 15. Diagram of the Inputs to Calculate the Lever Arm of the Opening Force Figure 16. Diagram of the Inputs to Calculate Maximum Pressure Difference When Opening the Stairwell Door Figure 17. Diagram of the Inputs to Calculate Maximum Pressure Difference When Opening the Suite Entrance Door Figure 18. Diagram of the Inputs to Calculate Maximum Pressure Difference When Closing the Suite Entrance Door Figure 19. Simulated Pressure Difference in Base Model Figure 20. Simulated Pressure Difference from Model A Figure 21. Simulated Pressure from Model B xi

12 Figure 22. Simulated Pressure from Model C Figure 23. Simulated Pressure Difference from Model D Figure 24. Simulated Pressure Difference from Model E Figure 25. Simulated Pressure Difference from Model F Figure 26. Simulated Pressure Difference from Model G Figure 27. Simulated Pressure from Model H xii

13 List of Acronyms ACH50 ADA ANSI ASHRAE ASTM BHMA CAN/CGSB CO CMHC ELA ERV HRV HVAC LEED MURB NBC NE NIST NPP SE SEC TDC USACE WSEC Air Change per Hour at 50 Pa Americans with Disabilities Act American National Standards Institute American Society of Heating, Refrigerating and Air- Conditioning Engineers American Society for Testing and Materials Builders Hardware Manufacturers Association Canadian General Standards Board Carbon Monoxide Canada Mortgage and Housing Corporation Effective Leakage Area Energy Recovery Ventilator Heat Recovery Ventilator Heating, Ventilation, and Air Conditioning Leadership in Energy and Environmental Design Multi-unit Residential Building National Building Code Northeast National Institute of Standards and Technology Neutral Pressure Plane Southeast Seattle Energy Code Thermal Draft Coefficient United States Army Corps of Engineers Washington State Energy Code xiii

14 Chapter 1 Introduction Recent developments in structural and construction techniques have increased the height of buildings worldwide. Many of these newly constructed high-rise buildings contain residential spaces that dramatically improve urban land use efficiency. Meanwhile, the increased height has brought many challenges. One of those emerging challenges is stack effect. Although stack forces exist in all buildings when there are air density differences between the indoor and outdoor environment, the magnitude of the stack pressure is small in low-rise buildings. However, stack effect can no longer be ignored in the building design of tall buildings. Although stack effect in high-rise buildings has been researched extensively, it was primarily discussed within the context of fire events. If a fire source is located on the lower levels, the smoke can propagate throughout the building by airflows generated by stack effect, and can result in fatalities on the upper floors. However, the knowledge and strategies developed for overcoming the stack effect during a fire cannot be directly applied to the daily operation scenarios. For instance, during a fire event, the elevator cars automatically return to the ground floor with the elevator doors open. A pressurization system is activated in the stairwells to prevent smoke from entering the egress shaft. A mitigation strategy tailored for tall residential buildings under normal operating conditions must instead prevent excessive stack pressure and provide tenants a healthy, comfortable, and sustainable living space. 1.1 Background Airflow due to stack effect is caused by air density differences between the indoor and outdoor environment. These air density differences arise because of the temperature differences between inside and outside air, which then create air pressure differences that lead to airflow. Stack affects all buildings including one-story houses, but the effects are magnified in skyscrapers. In early research, a number of mitigation strategies were promoted to reduce the impact of stack action. Common means used in those mitigation strategies included using the mechanical system 1

15 to change the air pressure within buildings, and addressing the airtightness of building components to resist air pressure differences and airflows. Some of the strategies were not capable of resisting stack pressures when the building scale was significantly increased or when occupant behavior counteracted the strategy, as in multiunit residential buildings (MURBs). Compartmentalization stands as one of the most promising solutions to stack-related problems in tall residential buildings. This approach addresses the airtightness around individual building components (suites, corridors, and vertical shafts) to create multiple air barriers. Those barriers are effective in reducing major airflow across the building envelope and redistributing the total pressure differences across multiple partitions. Although previous studies suggested compartmentalization in MURBs, very few assessed the effectiveness of compartmentalization in tall residential buildings. The lack of information may be due to the difficulties in conducting field tests in larger buildings with large volumes and complex floor layouts. Many questions arise regarding the implementation of compartmentalization. The first relates to whether a building needs to be fully or partially compartmentalized to be effective. Making every building component airtight would likely achieve the best results in reducing problems associated with stack effect, but it would increase building design specifications, make construction more difficult, take more time, and increase costs. Even though airtightness is addressed in some building codes and sustainable building guidelines, there is little quantitative data on the potential benefits of airtightness improvements. Establishing a quantitative relationship between the building airtightness and the mitigation of stack effect is important to illustrate to industry practitioners. Other questions related to quality control focus on the need for a reasonably simple field measurement protocol. Some of the currently available testing methods are not able to provide sufficient information on the building airtightness, or are too difficult to implement and only used for research purposes. This research aims to address these questions and to provide a holistic view of implementing the compartmentalization strategy. 2

16 1.2 Objectives The overall purpose of this research is to mitigate the problems created by stack action in tall residential buildings. The objectives are to: a) Analyze the mitigation approaches suggested in the literature to reduce the impact of stack effect, and b) Evaluate the effectiveness of compartmentalization as a promising solution to stackinduced problems. The research has resulted in two papers. a) Compartmentalization as A Solution to Managing Stack Effect in Tall Residential Buildings, a conference paper published at the RBDCC 2018 in State College, PA, USA b) Using Modeling Approach to Evaluate the Effects of Compartmentalization on Stack Action in Tall Residential Buildings, which will be submitted to the Journal of Building and Environment 1.3 Scope This research focuses on the impact of stack effect in tall residential buildings in a cold climates. The magnitude of stack pressure depends on the density differences between the indoor and outdoor air as well as the height of the building. The air pressure differences in residential buildings are complicated by occupant behavior, such as opening doors and windows that break airtight barriers. Additional details with regard to the research scope can also be found in Sections and Methodology To achieve the research objectives, academic and regulatory literature were reviewed. Topics covered include the basics of stack effect, related issues in tall buildings, and the mitigation strategies currently deployed to address stack induced pressures and airflows. As the topic of research narrowed toward compartmentalization, it became clear that there was very little in the 3

17 literature that provided a numerical evaluation of this strategy beyond a descriptive analysis of the potential benefits. Airtightness is a primary indicator of compartmentalization in a building. Since there were many studies conducted in this area, the research was then redirected to the airtightness related literature including building code requirements, testing guidelines, and field measurement results. However, since there have been limited field measurements of airflows within high-rise residential buildings, no statistically significant conclusions on the effectiveness of compartmentalization can be drawn. In the second part this research, computer simulation methods were adopted to study incremental improvements achieved by compartmentalizing residential buildings. CONTAM [Dols and Polidoro, 2015], a simulation software typically used to evaluate the migration of air-borne contaminants throughout a building, has been used in many studies to develop the airflow network within buildings. Since very few field measurements have been reported for tall residential buildings, a simulation model was developed and calibrated using field test results from a 12-story multifamily residential building. Once the model was calibrated, the 12-story building was expanded to a 48-story tall residential building, thereby creating a baseline. A series of compartmentalization approaches with different building components were applied, and the resulting improvements on stack-action related issues are discuss in detail. 1.5 Organization of Thesis In Chapter 2, a conference paper titled Compartmentalization as A Solution to Managing Stack Effect in Tall Residential Buildings is presented. In this conference paper, the stack effect related problems were characterized into three main categories. Among a range of mitigation strategies, compartmentalization was identified as a promising solution to those problems. Moreover, the lack of information and difficulties in measuring the effectiveness of this strategy were also detailed in this review paper. In Chapter 3, Using a Modeling Approach to Evaluate the Effects of Compartmentalization on Stack Action in Tall Residential Buildings is presented. This paper which will be submitted to Building and Environment within 6 weeks of the completion of this thesis, evaluated the 4

18 potential benefits associated with compartmentalizing tall residential buildings using computer simulation. From the evolution process, five models with different compartmentalization strategies as well as their results were discussed here. A comprehensive evaluation of the effect of compartmentalization has been summarized in Chapter 4. Due to the space limit in the journal paper, only five models have been presented in Chapter 3. However, a total of nine models were constructed in this research to reflect the improvements by increasing airtightness of different building components. The remaining 4 models are described in Chapter 4. Details related to the computer modelling methods not presented in Chapter 3 are provided in the appendices. Appendix A provides more information regarding the calibration process, which includes assumptions made in the simulation model, the selection of field measurements to be used in the calibration process, and the analysis of the outputs from the calibrated model. In Appendix B, further details related to the evaluation metrics used in the evaluation process that could not be included in Chapter 3 are discussed. One of the evaluation criteria was the limitations of the pressure differential across a door, which was based on calculations by the authors. Assumptions and calculation steps are explicitly illustrated in Appendix B. Details of the simulation outputs can be found in Appendix C. These tables are supplementary to the simulation result discussion in Chapter 3 and Chapter 4. Appendix D contains detailed descriptions of the model inputs and a discussion of the simulation results of the nine models that are presented in Chapter 4. Although some analysis may be similar to Section 3.7, they are included to provide a comprehensive analysis of the compartmentalization strategies. 5

19 Chapter 2 Compartmentalization as a Solution to Managing Stack Effect in Tall Residential Buildings The entirety of Chapter 2 is published as: Li, J., McCabe, B., Pressnail, K., Shahi, A. Compartmentalization as a Solution to Managing Stack Effect in Tall Residential Buildings. 4 th Residential Building Design & Construction Conference. Pennsylvania State College, PA, USA, February 28 th to March 1 st, Abstract Air movement can have a major effect on the energy performance and serviceability of tall residential buildings. Airflow occurs vertically, through elevator shafts and stairwells, or laterally through doorways, operable windows, and leakage openings in the building envelope. Air movement is caused by pressure differences created by a combination of stack effect, wind effect, mechanical ventilation, and elevator piston effect. However, during the heating season, stack effect is a major contributor to air movement in tall residential buildings in cold climates. The first objective of this paper is to review stack effect related issues in tall residential buildings. Three problems are summarized from issues commonly reported, which are life safety, serviceability, and ventilation related issues. Several mitigation strategies including active and passive strategies are discussed in this paper, as well as their limitations when applied to tall residential buildings. This paper then identifies compartmentalization as a reliable approach to mitigating stack effect induced problems. Compartmentalization is an effective solution for controlling airflows in tall residential buildings, especially air flows related to occupants opening windows or balcony doors. Assessing the extent to which tall residential buildings are currently being compartmentalized is difficult because field measurement data are generally, unavailable. Hence, the third goal of this 6

20 paper is to investigate ways in which airtightness data can be gathered in order to evaluate the effectiveness of compartmentalization. This paper examines three common challenges when conducting airtightness test in tall residential buildings, which are inconsistency in testing method, airtightness metric and documented normalized surface area. 2.2 Stack Effect Stack effect, refers to the movement of air in a building and through openings in a building s envelope due to temperature differences between the inside and the outside of the building; the taller the building, the greater the effect (Hutcheon & Handegord, 1994; Tamura & Wilson, 1968). As shown in Figure 1, the air movement occurs when we condition air by heating it in winter and cooling it in summer. Cold air is more dense than warm air, resulting in a difference in pressure across the building envelope. Conditioned indoor air Temperature difference between indoor and outdoor air Density difference between indoor and outdoor air Pressure difference across building envelope Air is driven through openings in the building envelope Figure 1. Diagram to Illustrate Stack Effect Driver During the heating season, under calm wind conditions with no fans operating, the dense cold outdoor air at the ground level is at a higher pressure than the warm indoor air. This pressure difference is greatest at the ground level, driving cold air into the building (infiltration). The warm conditioned air rises toward the upper levels where it exfiltrates. Somewhere between the ground and the top floor, the inside and outside air pressures are equal; this is called the neutral pressure plane. Similar airflows take place in conditioned shafts and stairwells within a building. 7

21 A reversal of this airflow occurs during the summer when the air inside the building is being cooled below the temperature of the outside air. This is known as reverse stack effect Problems Related to Stack Effect Stack effect induced problems in tall residential buildings are numerous and have been extensively investigated and reported (Hill, 2006; Jo, Lim, Song, Yeo, & Kim, 2007; Song, Lim, Lee, & Seo, 2014). This paper summarizes and classifies these problems into three categories: life safety, serviceability, and ventilation related issues. The most severe safety hazard is a fire event. Driven by pressure differentials, the rising smoke and other air-borne contaminants account for most of the fatalities in a fire event. The 26-story MGM Grand Casino Hotel in the 1980 s is a well-documented example (Best & Demers, 1982). The fire broke out on the ground floor of the hotel, then the smoke migrated vertically throughout the building. Sixty-one of the 85 fatalities that occurred above the 16 th floor were due to smoke inhalation (Klote, 2015). In less catastrophic situations, stack pressures can drive cooking odors, tobacco smoke, and other air-borne contaminants between suites, significantly affecting the indoor air quality in multiunit residential buildings (MURBs). The second category is building serviceability. A high air pressure differential can cause difficulties in operating swing doors and elevator doors, especially for those located at the ground or top floors (Tamblyn, 1991). To maintain smooth operation, studies have suggested that the maximum pressure difference across a single swing door should be 50 Pa, and 25 Pa for elevator landing doors (Lovatt & Wilson, 1994; Tamblyn, 1993). Other serviceability issues include whistling noises and uncomfortable air flow volumes that can adversely affect occupant comfort. From a field study involving a 40- and a 69-story residential building in Korea, the measured pressure differentials across swing doors and elevators were found to exceed the suggested pressure difference limits and the unpleasant whistling sounds were found to be as loud as db (Jo et al., 2007; Koo, Jo, Seo, Yeo, & Kim, 2004). 8

22 The third category is the ventilation system efficiency. Corridor ventilation systems, commonly used in residential buildings in Canada, use fresh outdoor air to pressurize the common corridors and drive ventilation air into units. To provide sufficient ventilation air to the suites, the ventilation system requires large amounts of outdoor air to overcome the pressure differences induce by stack effect. One study of mid- and high-rise residential buildings in British Columbia found by simulation that an average of 19% of the annual energy was used for ventilation heating (Finch, Burnett, & Knowles, 2009). In Canada s colder regions, a simulation study found that up to 25% of space heating energy use was associated with the ventilation system (CMHC, 2017). More details regarding the corridor ventilation system can be found in Section Stack Effect in Tall Buildings vs Low- rise Buildings The magnitude of stack effect is proportional to the indoor/outdoor air density difference and the building height. For two buildings in the same general location, the taller building would experience a stronger stack effect. For low- to mid-rise buildings, stack pressure differences are relatively small. Hence, the air movement within the building is dominated by either windinduced pressure differences or pressure differences induced by mechanical ventilation. Therefore, problems associated with stack effect and air leakage are exacerbated in tall buildings, which can have serious impacts on building performance. A graphical illustration of the stack pressure variation versus height above the neutral pressure plane is shown in Figure 2 for various temperature differences (Hutcheon & Handegord, 1994). For a 30-story building, assuming the neutral pressure plane is located at mid-height, a stack pressure difference around 60 Pa will develop when the outdoor air temperature is -10 o C and the indoor air temperature is 20 o C. 9

23 Stack Effect [Pa] Stack Effect vs Distance from Neutral Pressure Level and Various Temperature Differences Distance From Neutral Pressure Level [m] 50 K 40 K 30 K 20 K 10 K Figure 2.Theoretical Pressure Differential due to Stack Effect Applied on Buildings (Adapted from Hutcheon & Handegord, 1994) The definition of a tall building varies by source, and can be based on the building height or the number of floors. The concept of a tall building is subjective depending on its surrounding environment, the height to width ratio of the building, and the implementation of tall building related technologies (CTBUH, 2017). A more quantitative definition is a building taller than 91m (ASHRAE, n.d.). As such, a tall building in this paper is defined as a building taller than 90 m or approximately 30 stories, which is shown at the far right of Figure Stack Effect in Residential Buildings vs Commercial Buildings In addition to building height, the impact of stack-induced problems varies by building type. For instance, problems associated with stack effect can be more serious and difficult to control in residential buildings than in commercial offices. Commercial buildings often lack operable windows. If constructed reasonably airtight, the wall provides a reliable barrier to air movement across the building envelope. Residential buildings, on the other hand, typically have operable windows and balcony doors - important features to residential occupants. These openings compromise the building s airtightness and enhance air leakage due to the stack effect when 10

24 doors and windows are opened or incompletely closed. Occupant behavior is therefore a critical factor, making residential buildings particularly problematic in the control of air movement. Another difference between commercial and residential building is the existence of internal partitions which can make operating elevator and stairwell doors a larger problem for residential buildings. Field measurements at a 44-story office building in Montreal showed that the pressure differences across elevator landing doors at some floors exceeded the operation threshold by as much as 4 times (Lovatt & Wilson, 1994). In the open floor plans of many office buildings, most of the stack pressure differences are concentrated across the exterior enclosure (63% - 82%) (Tamura & Wilson, 1968). In a residential building with the same exterior façade airtightness and building height, the stack pressures from the exterior enclosure are often redistributed across the internal partitions and elevator and stairwell doors, potentially increasing the pressure difference at the operable doors Scope and Objectives Tall residential buildings in cold climates experience serious stack effect related problems. Factors that contribute include building height, inside-outside temperature difference, building envelope construction details, and, occupant behavior. This paper provides a review of existing literature on the means of mitigating stack effect in tall residential buildings in cold climates. The specific objectives of this research are: 1. To review stack effect related issues in tall residential buildings; 2. To evaluate active and passive approaches suggested in the literature to mitigate stack effect, and 3. To investigate the limitations of current methods for testing the successful implementation of compartmentalization, a promising mitigation strategy. 11

25 2.3 Approaches to Mitigate Stack Induced Problems Reliable and effective solutions to mitigate issues induced by stack effect is critical especially for tall residential buildings. The literature provides recommendations for mitigating strategies, which have been categorized here as active and passive strategies Active Strategies The active approach used to control the impact of stack effect involves adjusting indoor air pressures using mechanical systems. Some active strategies mentioned in the literature include Mechanical Pressurization Systems and Mechanical Ventilation of the Elevator Shaft Space Mechanical Pressurization System The mechanical pressurization system reduces the influence of stack effect by pressurizing all floors or partially including the lobby entrance (Tamblyn, 1993). Outdoor air is taken from an air handling unit on the rooftop and then distributed to the corridor on each floor. Due to a higher pressure, the corridor air is forced to the living unit through suite entrance door undercuts, and eventually pushed to the outside. But the mechanical pressurization system fails to consider the overall stack pressure distribution in a building. A study conducted on a 13-story MURB suggested the lower and upper portions of the building were significantly under- and over-ventilated respectively (Ricketts & Straube, 2014). The negative stack pressure on the lower portion of the building neutralizes the positive ventilation pressure across the suite envelope. Meanwhile, the exfiltration airflow is a combination of both outward ventilation and stack-induced flows on upper floors. Moreover, as a ventilation system, it fails to deliver fresh air at the designed rate to the suites. From the same study, researchers found that only 8% of air brought in by the air handling unit made its way through the duct system into the corridor, and into the suites through unit entrance door undercuts. The remaining 92% of conditioned air contributed to the uncontrolled airflows in the 12

26 building (Ricketts & Straube, 2014). Therefore, this strategy as a solution to managing stack effect problems may not be very effective in practice Mechanical Ventilation in Elevator Shaft Space Mechanically ventilating elevator shaft spaces reduces the stack-induced pressure differences by changing the air temperature inside the elevator shaft. This can be achieved by introducing outdoor air to the shaft through several diffusers, and ventilation openings located on the roof top to keep the shaft space from being pressurized. During the heating season, the air density inside the shaft increases when it is mixed with outdoor cold air. Hence, the pressure difference at the bottom and top of the building can be reduced. In one study, the mechanical ventilation system was installed in a 41-story commercial building. By cooling the average temperature of the elevator shaft by 5 o C, the velocity of air passing through elevator doors was reduced by 41% at the lobby level and 48% at the top floor when elevator doors were open (Song et al., 2014). However, secondary problems may occur when lowering the air temperature in elevator shafts, such as condensation on the shaft walls, occupant discomfort, and increasing heat losses from warmer zones in the building. The most concerning issue is the resistance to non-stack driven airflows. Since the elevator hoist is connected to the outside at the top of buildings, the ventilation fan and leaks at the roof can significantly enhance the airflow through the building. Although the stack pressure difference potential is reduced, the system has no resistance to airflow generated by strong winds and the building ventilation system. Therefore, ventilating the elevator shaft is not a favorable solution Passive Strategies Relative to active strategies, passive mitigation is a more reliable approach to control varying airflows by restricting flow paths. Five passive strategies are discussed next. 13

27 Vertical Zoning In vertical zoning, elevator travel is restricted to designated floors. One common application is the disconnection between the garage and upper residential floors. Passengers in the garage must take the elevator to the lobby floor, then transfer to another elevator to access their suites. It is more effective in preventing garage air from migrating into residential floors. In some tall buildings, there are three elevator zones for high-, mid- and low-rise floors. Field measurement found that vertical zoning is able to mitigate stack pressures and airflow excepting for the floor where two elevator zones meet each other (Jo et al., 2007). However, the downside is the inconvenience for residents since they may need to transfer elevators for a single trip. Also, vertical zoning requires several sets of elevator banks, which may result in inefficient floor area use as well as the construction cost Revolving Door and Vestibule The use of revolving doors and vestibules is a very successful solution to managing air infiltration or exfiltration due to stack pressures that has been implemented almost in every highrise residential and commercial tower. The revolving door can be easily operated since the stack pressure exerting on one glazing door is balanced by the pressure on the other panel. In the cold seasons, the amount of cold air that can rush into the lobby is limited by the volume between two door panels. For vestibules, the stack pressure differences are redistributed between a set of swing doors. Hence, it reduces the actual pressure difference cross each door panel to below the operation threshold. Field measurements conducted on 23 buildings concluded that the building main entrance doors can account for nearly 30 to 70% of the air leakage due to stack effect (Hutcheon & Handegord, 1994). Therefore, revolving doors and vestibules are frequently suggested (Jo et al., 2007; Lee, Hwang, Song, & Kim, 2012; Tamura & Wilson, 1968). The effectiveness of this strategy can be compromised by occupant behavior. For instance, an open window on the second floor can provide an infiltration path and shortcut the air barrier design of building entrance doors. Holding both doors open in the vestibule can also reduce their 14

28 effectiveness. Moreover, the use of revolving doors and vestibules is limited by the architectural layout of the lobby, which sometimes makes the installation impossible in a retrofitted building Improving Exterior Envelope Airtightness Another passive mitigation strategy is improving the airtightness of the entire building. The building enclosure is often treated as the primary air barrier system because it separates the indoor air from the ambient (Lovatt & Wilson, 1994; Tamura & Wilson, 1968). Having the exterior envelope constructed airtight is essential in reducing air exfiltration. It has achieved successful results in commercial buildings. However, for residential buildings, the benefits of having an airtight envelope are compromised by poorly sealed or open windows and balcony doors (CMHC, 1996). When windows are open, the indoor pressure of the suite becomes similar to the outdoor pressure. This increases the pressure difference across the demising wall between the suite and its adjacent units. Studies have shown that 12 to 36% of the total airflow into a suite can come from adjacent suites instead of the ambient environment (Levin, 1988; Palmiter, Heller, & Sherman, 1995). Field measurements conducted on six residential buildings in Minnesota found that on average 27% of the air leakage came from adjacent units (Bohac, Fitzgerald, Hewett, & Grimsrud, 2007). However, the results for individual units varied from 1% to 65% depending on the quality and type of construction. It was found that there was less air leakage at the demising wall if the building was newer, constructed with airtight material (concrete), or if the unit was located on a lower level (Bohac et al., 2007). A survey of the window opening frequency was conducted on a 15 and 17 story MURB in Winnipeg, Canada (Proskiw & Phillips, 2008). For the 17-story building, researchers observed that about 8.8%, 7.0% and 2.3% of suite windows would be opened when the ambient temperature is at 20 C, -4 C and -25 C respectively. Windows in the 15-story building were left open even at temperatures of - 40 C. Moreover, the frequency of leaving a window open was related to its location in the building. During -25 C weather, 1-2% of the windows were left open on lower floors, while 5-10% were open on the floors above the neutral pressure plane. 15

29 This demonstrates that the in-situ airtightness of the building envelope is not directly related to the design and workmanship; instead, occupant behavior can dramatically affect the effective airtightness of a building Improving Interior Partitions Airtightness Air leakage through interior partitions occurs at the top and bottom of the walls, wall penetrations, floor penetrations at utility stack runs, and around suite doors. Similar to building envelope issues, the effort spent on air barrier materials and assembly sealing details on interior elements can be discounted when the suite-corridor door is opened. As stack pressure difference found across the demising walls, the suite entrance, stairwell and elevator doors increases, these doors become more difficult to operate Improving both Exterior and Interior Partitions Airtightness To effectively mitigate stack effect, both exterior and interior air tightness should be improved. This leads to the introduction of compartmentalization, which is discussed next. 2.4 Compartmentalization The goal of compartmentalization is to separate each zone from its surrounding space in multizone buildings. Instead of looking at the building as a whole, vertical shafts, corridors, and suite units are isolated and disconnected when the doorways are closed. Isolation can be achieved by installing a continuous air barrier system along the perimeter of each zone. However, during construction, careful attention must be directed toward connections and pipe penetrations at the boundaries of the zones. Compartmentalization can achieve a variety of goals by limiting the vertical and horizontal air movement across building spaces (CMHC, 2005; Finch, Straube, & Genge, 2009; RDH, 2013). These include: 1. Increasing occupant comfort by providing a better control of indoor air temperature and relative humidity; 16

30 2. Reducing the energy consumption of space conditioning (heating and cooling); 3. Improving smoke migration control in a fire event; 4. Preventing migration of odors, tobacco, and cooking smoke from adjacent units; and, 5. Enhancing reliable ventilation in the suite space and downsize the ventilation equipment for the common area. The greatest advantage of compartmentalization is moderating the effect of occupant behavior. By creating multiple interior partitions, compartmentalization effectively reduces the possibility of a resistant-free airflow path across the building. For instance, when a suite window is open, partition walls around the suite function as a secondary air barrier system, preventing airflow into adjacent spaces. The concept of compartmentalization specifically targets residential buildings Approaches to Implementing Compartmentalization There are three approaches to executing the compartmentalization strategy (CMHC, 1996). The first one is referred to as unit compartmentalization. By addressing the airtightness of enclosures on all six sides, the suite is isolated from the adjacent living units, corridors, and the ambient environment. For the rest of the building, vertical shafts remain connected to the corridor on each level. The second method is the floor-by-floor compartmentalization. The objective of this approach is to reduce stack effect by preventing the vertical flow of air. It is achieved by ensuring airtightness between the corridors on each floor and the vertical shaft, such as elevators, stairwells, and utility runs, leaving the corridor and suites connected. Unfortunately, it is difficult to make the elevator landing doors airtight, due to limits on their maximum closing power. This method is commonly adopted in commercial buildings, with the implementation of elevator lobby vestibules on every floor. One potential problem associated with the first two methods is the pressure differential that develops at the airtightness partition layer. The high air pressure differential can exceed the 17

31 pressure thresholds, resulting in difficulty operating doors and the development of whistling noises around doors (CMHC, 1996). Finally, double compartmentalization is a hybrid strategy that emphases airtightness on both the suite and floor level. In this way, stack pressures can be redistributed throughout multiple internal partitions and the exterior envelope, so that the problems related to accumulated pressure can be mitigated. However, double compartmentalization increases the amount of time and cost required to ensure properly sealed interiors. In 1996, a 12-story residential building in Nepean, Ontario was used to test different compartmentalization strategies (CMHC, 1996). The stack pressures and airflows in the existing building were measured, and a computer modeling software, CONTAM [Dols and Polidoro, 2015], was used to simulate results from the three approaches. In the model, each compartmentalization strategy was simulated by replacing the suite or elevator landing doors with the most airtight doors, available at that time. It was estimated that the total airflow entering the building could be reduced by 12%, 4%, and 14% respectively using unit, floor-by-floor and double compartmentalization strategies. Even though the double compartmentalization achieved the best performance at 14%, unit compartmentalization (12%) was more cost-effective and recommended by the study. The modelling results also demonstrated that compartmentalization could be used to control the effect of opening windows and doors. In the model, one door (e.g. suite or elevator landing door) on the top floor was set to open, and the pressure differential and airflow rate was calculated for a unit on the middle floor and ground floor. For all three types of compartmentalization, the pressure exerted on the suite door at the 1st and 6th level remained the same as the all doors closed scenario. Therefore, the compartmentalization strategy is indeed effective in reducing stack induced pressure differences and airflows while accounting for occupant behavior. However, the unit compartmentalization strategy is not always preferred, especially in very tall towers. For high-rise and tall residential buildings, the pressure differential across suite entrance doors from unit compartmentalization can greatly exceed the allowable operation threshold of 50 18

32 Pa. Hence, there is a practical limitation for improving the airtightness of unit enclosures, so that a double compartmentalization strategy is required for tall residential buildings. 2.5 Assessment of Compartmentalization in Tall Residential Buildings Air leakage rates can be used to quantify the airtightness of an interior partition or exterior enclosure. It can also act as an indicator of the level of compartmentalization that a building has achieved. Hence, airtightness values for existing MURBs, if they were available, could be very helpful in assessing the effectiveness of compartmentalization strategies in existing tall residential buildings. Table 1 summarizes previous studies of MURB s leakage assessment. Because the results were expressed in different metrics, all airtightness values are converted into Normalized Flow Index as L/s/m 2 at 75 Pa for comparison purpose. Table 1. List of Previous Field Measurements on Airtightness of Existing MURBs Previous Study (Gulay, Stewart, & Foley, 1993) (CMHC, 2005) (Hill, 2006) (Finch, Straube, et al., 2009) (Klocke, Faakye, & Puttagunta, 2014) Number of Buildings Canada Canada Canada Canada USA Building Location Various British Ontario - Location Colombia New York Building Construction Time Near s- 2000s 2013 Building Height [Story] Whole Testing Method Building Suite/Floor Suite/Floor Guarded Suite/Floor Test & Blower Blower Blower Blower Guarded Door Test Door Test Door Test Door Test Blower Door Test Airtightness of Interior Partition [L/s/m2 at 75 Pa] Min Max Mean Min Max

33 Airtightness of Exterior Envelope Mean [L/s/m2 at 75 Pa] Airtightness of Min Suite Enclosure Max [L/s/m2 at 75 Pa] Mean Note A B C D E Previous Study (Ueno & Lstiburek, 2015) (CMHC, 2001) (RDH, 2013) (RDH, 2015) (Jones, Brown, Thompson, & Finch, 2014) Number of Buildings Canada, Canada, USA Canada USA USA USA, UK Building Location Washington Various Various Various Washington D.C. Location Location Location Building Construction Time After 2010 Building Height [Story] Suite/Floor Whole Whole Testing Method Blower Building Building Whole Door Test & Test & Test & Building Guarded Guarded Guarded Test Blower Blower Blower Door Test Door Test Door Test Airtightness of Interior Partition [L/s/m2 at 75 Pa] Airtightness of Exterior Envelope [L/s/m2 at 75 Pa] Airtightness of Suite Enclosure [L/s/m2 at 75 Pa] Note: Whole Building Test Min Max Mean Min Max Mean Min Max Mean Note F G H I J A. Airtightness value converted from Normalized Flow Index at 50 Pa B. The whole building test was conducted on the suite level C. The whole building test was conducted on the suite level D. Airtightness value converted from ELA50 and ACH50 E. The whole building test was conducted on the suite level; Airtightness value converted from Normalized Flow Index at 50 Pa and ACH50 F. Leakage flow occurred during guarded blower door test, because the cavity within suite adiabatic wall was connected to the ambient G. The whole building test was conducted on the suite, floor and building level 20

34 H. There are 6 suites tested under guarded blower door test. The significant low overall suite leakage is likely due to the design intention for LEED requirements I. Comparing with the previous literature review by the same author, there is only one 25- story MURB added into the database for buildings above 20 floors J. There is no further declaration on building height, completion time and other details. The building information is assumed in accordance with the SEC 2009 building code A review of over 100 publications related to airtightness around the world (Sherman & Chan, 2006) showed that most of the field measurement studies in North America were performed on low-rise (Lagus & King, 1986; Reardon, 1987; Love, 1990) to mid-rise (Shaw et al. 1991, Palmiter et al. 1995, Nichols & Gerbasi 1997, and Zuercher & Feustel 1983) residential buildings. Unfortunately, these works did not focus on stack effect as it is not significant at these limited building heights. No airtightness data for buildings over 30 stories were found. In the story range, the available test results are limited to four high-rise residential buildings. Ten units in two 29-story residential buildings were tested using a single blower fan to depressurize the suite space, hereby the airtightness of the suite enclosure were tested (CMHC, 2005; Hill, 2006). Although the building information is not clearly documented in Hill 2006, the context suggests that the two tested buildings are the same. In a 26-story residential building (Finch, Straube, et al., 2009), guarded blower door tests were conducted for one unit, which provided separate airtightness results of the suite enclosure, exterior envelope and internal partitions. Since the floor-to-ceiling height was not provided in the report, it was assumed to be 2.44m when converting the airtightness unit in Table 1. The airtightness rate of a 25-story building exterior envelope was estimated to be around 0.8 L/s/m 2 at 75 Pa, using a whole building test (RDH, 2015). It is difficult to compare the airtightness results from these few buildings given the diversity in testing methods and objectives. Therefore, these three measured sample points are insufficient to draw statistically significant conclusions on the general airtightness characteristics of tall residential buildings. The next section explains why airtightness measurements in tall residential buildings are so challenging. 21

35 2.6 Limitations in Measuring Airtightness in Tall Residential Buildings Compartmentalization has the potential to be an effective and reliable solution for tall residential buildings. However, there is little empirical evidence that compartmentalization has been successfully implemented in tall residential buildings. To understand why the data are not available, three difficulties in applying the current airtightness assessment process to tall residential buildings are analyzed; these difficulties include: inconsistency in testing method; airtightness metrics; and normalized surface area calculations Inconsistency in Testing Methods There are two commonly adopted testing methods for testing airtightness in North America: whole building tests, and guarded blower door tests. Each testing scheme has unique advantages, as well as practical limitations. Hence there is no universal agreement on airtightness testing procedures for multiunit residential buildings Whole Building Test The whole building test was first developed to gather information about air leakage in single detached houses. By depressurizing the entire house using a blower door fan, the airflow across the building envelope can be calculated and the overall leakage rate determined. Eventually, fan depressurization was widely adopted in North America as a means to evaluate the airtightness of single-family detached homes. However, the whole building test has practical limits when testing large volume spaces, and cannot be readily used to evaluate the airtightness of large buildings. The first limiting factor is the building volume (RDH, 2015; Sherman & Chan, 2006; Urquhart, Richman, & Finch, 2015). For buildings with large floor areas, the conventional blower fan used for testing houses is not capable of providing sufficient flow to develop a large pressure difference. For instance, to test a building over 1000 m 2, either multiple blower doors need to operated simultaneously, or a single high capacity fan can be installed to depressurize or pressurize the building (Straube, 2014). The accuracy of the field test data can be compromised 22

36 when multiple blowers operate simultaneously (CMHC, 2001). Conversely, operating the high capacity fan is extremely difficult from a logistical perspective, due to the lack of equipment, mobility issues, and additional power requirements. The second limiting factor is the testing conditions. Prior to the test, all of the intentional openings such as HVAC intakes and exhaust grills, kitchens and bathroom exhaust ducts, and relief dampers must be prepared (Straube, 2014). Three types of preparation can be done to those openings: sealed, closed, and untouched. In one field study, the measured leakage results extrapolated from depressurization and pressurization tests were contradictory because the passive exhaust fan was left intact (Urquhart et al., 2015). Errors can easily be introduced when testing residential buildings if the preparation procedure is not well defined and implemented. The third limiting factor relates to the control of windows and doorways. A study on whole building tests conducted on six occupied MURBs with 1 to 13 stories, summarized major difficulties related to field measurements (Red River College, 2015). a) Suite Entrance Door The whole building test requires a uniform pressure change in the entire tested space. Having the interior suite door closed could result in a pressure difference between a suite and the adjacent corridor being greater than 75 Pa, although the error in measured leakage was within a tolerable range (3% - 5%). As the experiments were performed on two small buildings (one-story and sixstory), one might expect that the impact of not having all the interior spaces connected will be much more severe as the building scale increases. b) Suite Window Window openings can greatly affect air leakage results. The field test found that results could not be used even if one single window was open. Although windows were closed prior to the test, many were found open either due to occupant interference or the force generated during the pressurization test. A crew was assigned to observe window conditions from the outside, and the test was paused several times to fix window issues. For tall residential buildings, it may be impractical to continuously monitor the position of each window. 23

37 c) Building Entrance Door Similar to open windows, building entrance doors can also significantly affect the test results. Access control must be implemented to ensure test consistency. It requires the full cooperation of the property management team and the tenants for occupied buildings, or a well-planned schedule with subcontractors and suppliers for buildings under construction. Lastly, the whole building test is only able to determine the airtightness of the exterior envelope of the building. It cannot provide information on interior party walls, which makes it unsuitable for investigating compartmentalization. The practical limits of conducting whole building tests make it extremely difficult and potentially unreliable for large buildings Guarded Blower Door Test To solve problems arising from larger scale buildings and complex connected floor plans, a method called guarded blower door test was developed to examine individual suites. This method isolates the test space by creating a guard or neutral pressures zones that completely surround the suite in question so that air leakage can be isolated to the building assembly of interest (Reardon & Shaw, 1988; Shaw, 1980). The guarded blower door test prevents leakages across interior partitions by maintaining the same pressure on each side of a partition, hereby eliminating the pressure differences across the partitions. This requires installing, running, and coordinating multiple fans in the spaces adjacent to the tested suite. In contrast to the whole building test, the guarded blower door test can provide airtightness information on both exterior and interior partitions. One advantage for high-rise residential buildings, is that the test is conducted at the suite level, rather than the full building. Many limitations identified in the whole building test can be mitigated using this testing method. However, the guarded blower door test is not widely used by practitioners in the building industry. The major practical difficulty is coordinating multiple running fans to eliminate the pressure difference across any internal partitions. For example, the pressure in the corridor is susceptible to the piston effect resulting from elevator motion. The opening of the elevator 24

38 landing doors has great impact on corridor pressures as well. The complex internal geometry in residential buildings increases the difficulty of maintaining a steady pressure, which compromises the measurement accuracy (CMHC, 2001; Urquhart et al., 2015). To combat the variables in field measurement, experienced personnel are required to perform the test, and strict protocols are needed to adjust for repeating experimental processes and to account for nonuniform testing conditions. Although the guarded blower door test is intended to eliminate the internal flow, the measured flow result may still include leakages through partitions due to demising wall construction. In one case (Ueno & Lstiburek, 2015), the wall cavities between adjacent units were unknowingly connected to the ambient environment. During the test, air leaked out from the pressurized unit and flowed to the outdoors through the wall cavity even though the pressure difference was balanced across the demising wall. It has been concluded that the guarded blower door test is too costly and time intensive to be applied as a common airtightness testing method (Finch, Straube, et al., 2009) Suite/Floor Level Blower Door Test Suite/Floor level blower door tests are an adaptation of the whole building test. Instead of conducting the test on the entire building, only one blower fan is required to be installed to (de)pressurize the individual suite or floor space. This testing method measures the overall airtightness of the suite or floor enclosure, including exterior walls, internal partitions, floor and ceiling slabs. This testing method is a promising means of measuring airtightness of compartmentalized residential buildings, since it requires cheaper equipment, less time for test preparation, simpler coordination and less access of the tested space. However, there is no standardized guidelines for conducting the suite/floor level blower door test. Previous field measurements used protocols for the whole building test as the general guidelines when conducting this alternative test. But errors can be introduced when interpolating and applying the guidelines differently. In the case of the 29-story building mentioned in Chapter 2.4, both studies conducted suite level blower door test following the CAN/CGSB

39 protocol that specifically developed for testing detached house using whole building test (CMHC, 2005; Hill, 2006). However, the fan was installed at the balcony door or window openings in one study, while the blower was located at the suite entrance door in the other project. The leakage that occurs where the fan is installed was not explicitly reflected in the measurement, hereby it creates difference in test results, even when testing on the same suite Inconsistency in Airtightness Metrics A proper metric is essential to reflect the in-situ airtightness for the air barrier system, and enables tested results to be compared. The selection of unit depends on and varies by the testing method. In this section, airtightness metrics are introduced. Finally, an appropriate unit for tall residential buildings is recommended Air Change Rate A common metric used in airtightness testing is air changes per hour at a 50 Pa pressure difference (ACH50). ACH50 represents the number of times that the air inside a space is replaced per hour when the pressure differential across the enclosure surface is 50 Pa. The metric is calculated by dividing the total air leakage flow in one hour by the space volume. ACH50 is a good indicator when the tested target has a relatively large floor area such as detached houses. But results expressed in ACH50 for relatively small volume-to-surface ratio spaces can be misleading and seem much leakier than they are. Consider two suites from one residential building - the airtightness rate of each suite should be reasonably similar, say, 2 L/s/m 2 of flow area at 75 Pa. But one suite contains three bedrooms with a floor area of 120 m 2, while the other is a 50 m 2 bachelor suite. Converting the airtightness value to ACH50, the larger suite becomes 5.73 ACH50 and the bachelor suite with a smaller volume-to-surface ratio seems much leakier at 7.02 ACH50. Therefore, users of ACH50 to evaluate the airtightness level of a condominium suit should keep in mind that the results may be biased for different sized suites and those with significantly different geometries (Urquhart et al., 2015). 26

40 Normalized Airflow Rate The normalized rate presents an averaged airtightness without the variance of space volume and geometry. It is useful when comparing two test spaces with significantly different geometries and volumes. Most of the airtightness requirements and codes for commercial buildings are stated in this metric, noted as L/s/m 2 or CFM/ft 2 at 75 Pa where the results are normalized by dividing the air leakage rate by the surface area through which the leakage occurs. In this paper, normalized airflow rate is recommended to be the metric for airtightness measurement for tall residential buildings Leakage Area There are three metrics containing the phrase leakage area. The first is equivalent leakage area, which describes the size of an equivalent sharp-edge orifice that would generate an airflow at 10 Pa equal to that measured in a leakage test. It is used in the CAN/CGSB standard (CAN/CGSB, 1986). The second, effective leakage area, is the same as the equivalent leakage area but at 4Pa, as mandated in ASTM E (ASTM, 2003). Neither metric is helpful in suite comparisons since they do not account for the total surface area through which the leakage occurs. Hence, a third metric, specific leakage area, is calculated by dividing the equivalent or effective leakage area by the enclosure area, similar to the normalized airflow rate. One author argues that normalized leakage area (specific leakage area in this context) is beneficial over other metrics since it allows a direct comparison among different tested spaces (Urquhart et al., 2015). But it might not be an ideal airtightness metric. Consider CAN/CGSB as an example. The specific leakage area is calculated based on the total airflow at 10 Pa. The flow rate at 10 Pa cannot be directly measured since 10 Pa is often too small to overcome other driven forces such as stack or wind pressures. Instead, the flow rate is estimated by developing a regression equation based on airflows measured from 50 Pa to 75 Pa 27

41 (CAN/CGSB, 1986). Compared to the normalized airflow rate, specific leakage area increases errors that might be introduced during the regression process and extrapolation process Inconsistency in Normalized Surface Area Calculation Enclosure area refers to the surface area of the boundary that separates the indoor environment from the ambient. However, it is an interpretation that can vary quite significantly (CMHC, 2001) to include only the exterior wall surface area to including roofs and foundations. Only the wall was used in some of the earliest applications, presumably because the leakage through the foundation and roof sections were sufficiently small or negligible. In Great Britain and the United States, the surface area of exterior walls and roofs were used for similar reasons. In some cases, floor areas were used rather than enclosure areas. Commonly, the normalized leakage data is stated without an accompanying definition of enclosure area. For a building tested according to the whole building test, it is the entire building envelope surface area (four exterior walls, roof, and foundation), that should be used to normalize the result. For guarded blower door tests, the exterior wall surface area for the suite is the only leakage section. Some articles also mentioned that whole building tests were conducted on the suite or floor level only, in which case the total six sides of surface area of the suite or floor would be a reasonable value for normalization. However, in practice, the normalized surface area is often mismatched according to the airtightness testing method. One report characterizing the leakage rate of existing large buildings, different normalizing areas were used, skewing the results and making comparisons unreliable (CMHC, 2001). 2.7 Conclusions Stack effect occurs in all types of buildings in cold climates. It is more significant in tall residential buildings because of the building height as well as the floor layout. The implementation of operable windows and balcony doors makes the control of stack effect induced airflows and pressures much difficult. This paper has identified and investigated some of the critical issues related to stack effect in tall residential buildings. Commonly mentioned in the 28

42 literature, these problems are migration of fire smoke, malfunction of elevator/stairwell doors, and inefficient ventilation system. A number of stack effect mitigation strategies noted in the literature were identified and analyzed. Compartmentalization, a promising passive strategy, can effectively redistribute pressures and reduce air flows induced by stack effect. By improving the airtightness of both internal and external partitioning, each suite can be isolated from the other spaces on that floor and on adjacent floors. The isolation of living units can reduce typical MURB problems, such as cross-contamination of odors, indoor air quality, and energy consumption. An early stage simulation has confirmed that compartmentalizing a building was able to control the impact of occupant behavior, which is a significant contributor to stack effect problems in residential buildings. When examining the implementation of compartmentalization in existing tall MURBs, no test data were available for the buildings within the research scope. The lack of airtightness information prevents substantial conclusions to be drawn on the success of compartmentalization. This paper then investigated the difficulties in acquiring airtightness data for tall residential buildings. The insufficient data are mainly due to: a) The lack of proper airtightness testing method specifically designed for tall residential buildings; b) The lack of a uniform metric for direct comparisons from different field testing measurements and c) The lack of a uniform definition of normalized area, and clearly documented information of the tested buildings. 2.8 Recommendations and Future Steps In order to develop a comprehensive understanding on the compartmentalization strategy as a solution to stack effect in tall residential buildings, this paper provides two recommendations. 29

43 The first recommended step is to further investigate the effectiveness of compartmentalizing residential buildings. A computer modeling using CONTAM was done in 1996, the change in airflows and pressure differences was simulated base on replacing suite entrance doors and elevator landing doors. However, there still is a need to quantify the relationship between the improvement on airtightness and the reduction in stack induced pressures and airflows. Currently, there are several airtightness targets for building exterior envelopes or suite enclosures suggested by building design codes or best practice programs. Those airtightness requirements can be utilized as the inputs to the simulation. Through computer modeling, the relationship between the change in stack induced pressure and airflows corresponding to different building airtightness can be evaluated. The second recommended step is to develop a standardized airtightness testing procedure specific for tall residential buildings. The purpose of this recommendation is to ease the field measurement process so that more airtightness data of tall residential buildings can be acquired for analysis. This paper suggests that the suite/floor level blower door test over other airtightness testing methods. It appears to be the most promising solution because it resolves limits of whole building test on large buildings, as well as avoids the sophisticate operation from guarded blower door test. Moreover, for new constructed buildings, the suite/floor level airtightness test can be integrated into the construction schedule, and the experience in airtight construction can be evaluated and transferable to the later construction work in higher floors. The suite/floor level blower door test has been often used and repeated in the literature. However, there is no standard protocol specific for blower door testing in tall residential buildings. Provisions, such as the location of the blower fan, and whether both de- and pressurization are required, need to be standardized to minimize errors occurred in the testing process. To promote the compartmentalization approach, it is important to provide practitioners with a feasible and simple tool to assess whether the requisite airtightness has been achieved. 30

44 Chapter 3 Using a Modeling Approach to Evaluate the Effects of Compartmentalization on Stack Action in Tall Residential Buildings The entire Chapter 3 is a technical paper that will be submitted for peer review. 3.1 Abstract Stack effect is the dominant driving force influencing the air pressures and airflows in tall residential buildings. Stack action results in many building performance issues including: fire safety; serviceability; and ventilation. Compartmentalization is one mitigation strategy that could reduce stack induced problems. However, there is little measured or simulated data that has been published supporting the effectiveness of this strategy. In this research project, a computer simulation was conducted on a study building to evaluate the effectiveness of compartmentalizing tall residential buildings. Five models were constructed and incremental changes were made to the base case building from no airtightness attention to full-scale compartmentalization. The simulation results suggested that both suite and floor level compartmentalization strategies along with adjustments in the HVAC system were required to reduce the likelihood of stack effect issues and to ensure proper building performance. Separating the parking garage level was identified as the third approach to compartmentalization, and its effectiveness was discussed separately in this paper. Results showed that, although it was important to prevent the garage air from entering the residential floors in terms of indoor air quality, the improvements to airflow achieved by separating the garage were relatively minor compared to the effects of applying compartmentalization strategies to all the residential floors. 3.2 Introduction Natural stack action is one of the driving forces affecting airflow in a building. Stack effect airflows result from pressure differentials that are created by density differences between the indoor and the outdoor air masses. These density differences result from air temperature differences (Hutcheon & Handegord, 1994). In winter, stack effect in tall buildings leads to air 31

45 infiltration at the lower floors and exfiltration on upper levels. Airflows are reversed in the summer when the air inside a building is cooler than the air outside Stack Effect in Tall Residential Buildings Other factors that lead to air pressures differences in buildings include wind, mechanical systems, and elevator movement. However, stack effect becomes a dominant factor with increases in building height (Ricketts, 2014). In a previous study of tall residential buildings, problems related to stack action were summarized into three categories: safety, serviceability, and ventilation (Li et. al., 2018). If stack pressures are not properly managed, buildings can suffer from a broad array of problems such as smoke and contaminated air migration, difficulty operating doors, over- and under-ventilated suite spaces, as well as excessive energy consumption for space conditioning Compartmentalization Active and passive strategies for mitigating the effects of stack action have been examined in previous studies (Jo, Lim, Song, Yeo, & Kim, 2007; Lovatt & Wilson, 1994; Song, Lim, Lee, & Seo, 2014; Tamblyn, 1993; Tamura & Wilson, 1968). Mechanical systems have been used to actively change the building air pressure regime. For example, corridors have been pressurized and elevator shafts have been ventilated with outdoor air. Passive strategies have also been implemented to mitigate the effects of stack action. These passive strategies include improving the resistance to the air movement within and across the building envelope. Physical barriers as well as vertical zoning, revolving doors, vestibules, and airtight exterior envelope are all passive strategies that can be used to control the effects of stack action. However, the effectiveness of these strategies depends upon the type of building. Residential buildings are particularly challenging to operate because of the existence of operable windows, numerous interior demising walls, and balcony doors (Li et al., 2018). Compartmentalization is one mitigation strategy that may reduce the impacts of stack effect in tall residential buildings (CMHC, 2005; Finch, Straube, & Genge, 2009; RDH, 2013). 32

46 Compartmentalization involves separating each zone from its surrounding space in a multi-zone structure. When compartmentalizing a residential building, the airtightness of both the exterior envelope and interior partitions should be achieved to create an airtight perimeter around each building element (e.g. elevator shafts, corridors, and suites). Multiple air barriers mitigate stackinduced problems by reducing the air exchange between two adjacent zones and distributing the significant stack pressures to dedicated partitions. Furthermore, the compartmentalization strategy moderates the impact of occupant behavior. When windows are open, the airtight suite perimeter becomes a secondary facade system, preventing a significant change in airflows and pressures in adjacent suites (CMHC, 1996) Effectiveness of Compartmentalization The compartmentalization strategy has great potential to be an effective and reliable solution for managing stack action in tall residential buildings. However, there is little published data from field measurements or computer simulations supporting the effectiveness of this strategy. A few field measurements in high-rise residential buildings have been reported in the literature. Yet no statistically significant conclusions can be made on the in-service effectiveness of compartmentalization (Li et al., 2018). An early study estimated the potential benefits of implementing compartmentalization strategy (CMHC, 1996), but limitations of the software then available and the limited number of building components that were included in the simulation may have affected the accuracy of the model outputs. 3.3 Objectives One of the barriers to the implementation of compartmentalization is the lack of published quantitative data that provide evidence of the effectiveness of compartmentalization. Thus, the primary objective of this paper is to quantitatively assess the effectiveness of compartmentalization in mitigating the adverse effects caused by stack action. The secondary goal of this research is to examine the extent to which compartmentalization can mitigate other building performance issues such as improper ventilation rate of suites and extensive energy consumption due to air leakages. 33

47 3.4 Methodology Stack-induced problems can be evaluated by examining air pressure differences and the resulting airflows. Air pressure differences between two zones determine the airflow direction through openings and affect practical functions such as the operability of doors. The magnitude of the resulting airflows affects the ventilation rates in zones and the associated energy needed to condition the air Nodal Analysis Network Due to the complexity of multi-family residential buildings, the pressure and airflow across each zone can be estimated using the nodal analysis approach (Ricketts, 2014). The flow relationship between two zones can be described by Q = C D P n, an empirical approximation for the airflow resulting from a pressure difference. However, there are two major assumptions in the nodal analysis approach that may cause the simulation results to deviate from the actual airflow network. First, in using the nodal analysis approach, it is assumed that the air in each zone is perfectly mixed. Second, it is assumed that no air travels within the boundary between two zones, but it might occur within the wall cavity between two suites (Ueno & Lstiburek, 2015). In the absence of comprehensive airflow data, these two assumptions are reasonable and allow the researcher to judge the relative effect of implementing the compartmentalization strategy. The nodal analysis network was adopted in this research using CONTAM [Dols and Polidoro, 2015], a computer simulation program that incorporates the nodal analysis approach into its algorithm. It was originally developed by the National Institute of Standards and Technology, and has been widely used for airflow simulation (Dols & Polidoro, 2015). 34

48 3.4.2 Research Methodology To construct a simulation model in CONTAM, the user must enter the building properties, including the typical floor plan layout, information about various building components, and the associated leakage values. During the calibration process, field test results of airflows and/or pressures are needed to improve the accuracy of the model. Due to the lack of data about airflows and pressures in tall residential buildings (above 90 m), an alternative approach was used in this research. First, a CONTAM model was developed for a 12- story multifamily residential building for which field measurement data were available. The field measurement data of that building were then used to calibrate the model. After calibration, the model was expanded by four times to become a 48-story tall residential tower with the same leakage characteristics as the 12-story building. The expanded model was treated as the Base Model to which a series of compartmentalization steps were applied and the associated benefits were analyzed. 3.5 Calibration The building selected for calibration was a 12-floor residential building located in Nepean, Ontario (CMHC, 1996). There were 17 suites on each residential floor including 13 twobedroom suites and 4 one-bedroom units. The residential floors were 1868 m 2, and the lobby level had a slightly greater floor area at 2248 m 2. The building was completed in 1990, and the field measurements on zonal pressures were conducted in 1995 when the building was relatively new and presumably had little damage or deterioration around building element joints or connections. Therefore, it was considered to be a good representation of a typical, newly constructed building where moderate attention had been paid to air sealing details. Floor plan layouts for a typical residential floor and ground lobby level are shown in Figure 3. 35

49 Figure 3.Schematic Floor Plan Layout of Ground Floor Lobby (Left) and Typical Residential Floor (Right) Assumptions in the model Two assumptions were made in conducting the building simulation using CONTAM. First, the indoor air temperature was assumed to be 20 C for all zones within the building. In reality, the indoor temperatures can vary throughout the building, and might not be uniform even within a zone (e.g. elevator shaft). However, because no temperature data were documented in the original report, a uniform temperature was applied to all zones for simplicity. The second assumption concerned the outdoor air delivery rate through the heating, ventilation, and air conditioning (HVAC) system. The flow rate through the ventilation grilles was tested on every floor in the original study. However, the HVAC airflow tests were not conducted in the same month when the pressure differences were measured. Also, the distribution of airflow 36

50 values suggested that the HVAC system may have been affected by occupant behavior. Therefore, the measured airflow rates might not reflect the HVAC system performance in the building. As an alternative, the design HVAC delivery rate was used in the model as well as in the calibration process. It was assumed in the model that a uniform ventilation rate of 727 L/s was delivered to the corridor space on every floor Data inputs used in calibration In the original study, the field testing involved measuring the difference in pressure between the point of interest and the north stairwell (CMHC, 1996). Although 19 sets of field testing data were collected, 10 out of the 19 were measured under windy conditions. They were not used for calibration because wind pressure was typically not steady and recorded values were sporadic over the entire testing process. Within the 9 no-wind datasets, 4 were performed with the HVAC system off. When HVAC fans were turned off, the system became a variable and the delivery rate was subjected to other factors such as hallway pressure and ductwork characteristics. Due to the lack of information of the duct size and connection details, it was difficult to produce a good HVAC system simulation model. In the remaining 5 tests, one test was conducted with all doors closed, while the remainder of the tests evaluated the impact of opening lobby entrance, lobby corridor, elevator and garage doors. Changing the door configuration could alter the pressure difference values to some extent, but the impact appeared to be minor and localized. Because the building was relatively leaky, opening one door did not dramatically change the performance on a whole building scale. The localized change in pressures could be observed from the measurement data as well. Due to many unknowns, the simulation model was calibrated to the single measurement set in which there was no wind, HVAC system operating, and all doors closed Calibration result The field testing measurements and the simulation results after calibration are shown in Table 2. With the exception of the elevator shaft, the calibrated model estimated the pressure difference at each sampling point within ±1.0 Pa of the field measurements. The 2.5 Pa difference at the 37

51 elevator might be due to additional leakage openings in the shaft which were not documented in the original report, or it could be an experimental error generated during the field measurement. Generally, the model, as calibrated, was a reasonable representation of the airflow characteristics of the building. Table 2. The Simulation Results after the Calibration Process Compared to the Field Measurements F12 F1 P1 Point Measured Field Measurement Pressure Difference (Pa) Calibrated Model Pressure Difference (Pa) Absolute Difference between Field and Model Results (Pa) Elevator Shaft Garbage Room Corridor Suite (Average) North Corridor Central Corridor Lobby Vestibule Suite (Average) Ambient Parking Garage Garbage Chute Shaft Evaluation of Compartmentalization Strategies After achieving a representative simulation model of a 12-story multi-family residential building, the next step was to scale the building model to a tall residential building. In this research project, the calibrated building model was scaled to 48 stories to simulate the stack effect in tall buildings Assumptions in the Base Model When increasing the number of floors from 12 to 48, several assumptions were made. These assumptions and the rationale for making them include: 38

52 a) The floor plan layout of the underground parking levels and ground floor in the 48-story tall residential building model (Base Model) remained the same as those in the calibrated 12-story MURB model. b) One additional elevator car was installed in the elevator bank (4 elevator cars in total) in the Base Model. There were no design provisions defining the minimum requirement of elevator cars in a building, and the selection was dependent on a series of factors such as the expected occupancy, acceptable waiting times, and elevator capacity, which was beyond the scope of this research work. For the purpose of simplification, the rate of 180 rooms per elevator car was adopted in this research project for an economy oriented elevator service, suggested by the general design guideline from TOSHIBA ( Elevator Traffic Planning, n.d.). c) Two stairwells were assumed in accordance with the Ontario Building Code , which required that every floor shall be served by at least two exits ( Ontario Building Code, 2015). d) In the Base Model, the HVAC delivery rate was the same as the design airflow rate from the calibrated model. To avoid changing the size of the HVAC ducts and the fan equipment, every 12 floors had a separate HVAC system providing fresh air to the corridor area, which was the same number of floors that the HVAC system was designed to service in the calibrated model Evaluation Metrics In accessing the effectiveness of compartmentalization, quantitative metrics were required to evaluate the improvements in building performance. The criteria in the metric incorporated four main categories: contaminant control, serviceability, suite ventilation, and total air infiltration. Contaminant control addresses the problem where the polluted air could migrate from the contamination source to other parts of the building through horizontal and vertical connections. Ideally, a slightly pressurized corridor is able to prevent suite odours, such as those from the kitchen, from entering the common area and other suites. 39

53 Serviceability emphasizes the issues in operating doors which were commonly discussed in previous studies. Elevator landing door malfunction and difficulty in opening stairwell doors occur when the pressure differences across those doors exceed the allowable threshold suggested in the literature (Lovatt & Wilson, 1994; Tamblyn, 1993). Not many studies mentioned the similar problem at the suite entrance door. However, weather-stripping the suite door would increase the pressure differential and eventually lead to serviceability issues. In this research, the allowable pressure difference across the suite door was estimated based on two factors: the maximum force to open an interior door defined in Americans with Disabilities Act (Department of Justice, 2010), and the greatest force a door closer can provide to fully close the suite door (Builders Hardware Manufacturers Association, 2013). A list of pressure difference thresholds used to evaluate serviceability can be found in Table 3. Table 3. Maximum Allowable Force and Pressure Difference across Different Doors Door Type Elevator Door Stairwell Door Suite Door Opening Max Force (N) - 90* 22* Max Pressure (Pa) 25* 59** 24** Closing Max Force (N) * Max Pressure (Pa) 25* - 21** Note: * Values were acquired directly from the literature (Builders Hardware Manufacturers Association, 2013; Department of Justice, 2010; Lovatt & Wilson, 1994; Tamblyn, 1993) ** Values were calculated by the author. Details can be found in Appendix B Suite ventilation refers to the ability of the HVAC system to provide proper ventilation for each suite in the building. According to ASHRAE 62.1, the outdoor fresh air delivery rate for a suite should be maintained around 40 L/s (ASHRAE, 2004). Proper ventilation means that sufficient fresh air can reach the tenant without increasing the energy consumption dramatically and causing other comfort issues. Last but not least, total air infiltration is associated with the energy used to condition the outdoor air to the desired room temperature. The total amount of air that requires conditioning can be sub-divided into two groups: controlled and uncontrolled airflow. The former is the amount of 40

54 outdoor air entering a building through the HVAC system at a controlled rate, while the latter accounts for uncontrolled air infiltration through the envelope openings. The greatest pressure difference and in/exfiltration rate due to stack action occurs at the greatest distance from the neutral pressure plane. Since the location of the neutral pressure plane is typically around the middle height of a building, the maximum pressure differences occur at floors 1 (F1) and 48 (F48). However, the ground floor has a different layout than the upper floors and the top floor has additional leakage areas connecting to the roof. Thus these floors are not representative of the rest of the building. Therefore, the pressure distribution and airflows on F2 and F47 were examined in this research project Compartmentalization Steps There are several approaches to compartmentalizing a residential building: suite-by-suite, floorby-floor, and a combination of suite and floor strategy (CMHC, 1996). Suite compartmentalization isolates individual suites from the rest of the building by improving the airtightness around the suite perimeter. On the other hand, floor compartmentalization addresses the separation between vertical shafts and each floor, leaving the corridor and suites on the same floor remaining connected. In this research, a step-by-step process of air tightening began with a building where little attention was paid to leakage sealing details. Then, a series of improvements were made to the building airtightness, which ultimately led to full compartmentalization. Simulations were carried out as each air-tightening step was taken. Subsequent steps relied upon previous steps to demonstrate the effect of cumulative improvements in building airtightness. As well, each incremental improvement was evaluated to identify the most effective airtightness measures to mitigate the adverse effects of stack action. The evaluation process was constructed with regard to the steps shown in Table 4. 41

55 Table 4. Computer Simulation Steps in Evaluating Compartmentalization Approaches Approach Step Name Description No Compartmentalization 1 Base Model No special attention made on airtightness Suite Compartmentalization Suite + Common Area Compartmentalization 2 SC1 Exterior envelope improvement 3 SC2 Interior partitions improvement & HVAC adjustment 4 FC1 Corridor separation improvement 5 FC2 Vestibule installation and HVAC adjustment 3.7 Result and Discussion Each compartmentalization step provided interesting results. Details of the model inputs and simulation results are discussed in the following sections, while a comprehensive building performance chart for all steps can be found in Appendix D Base Model: No Compartmentalization The Base Model provided a baseline scenario of buildings where little attention to airtightness was paid; therefore, the majority of the air leakage values from the calibrated MURB were used in this model except for the building envelope. Although steel frame and brick veneer were used in the 12-story MURB, most new high-rise residential buildings use the window wall system as their exterior facades. To achieve a better representation of a real tall residential building, the exterior envelope in the Base Model was replaced with a window wall system. For each suite, it was assumed that there was one 1 m by 1.6 m single horizontal slider window (two windows for corner suites), one 4 m 2 sliding door accessing the balcony, and a fixed window glazing system for the rest of the façade area. 42

56 Airtightness Inputs A typical leakage rate for window wall systems could not be found in the literature. Both NBC 2015 and SEC/WSEC 2012 suggest that the fixed portion of the window wall is categorized as a curtain wall system (Jones, Brown, Thompson, & Finch, 2014; Kayll, Torok, & Jutras, 2017). Therefore, the curtain wall value was used for the non-operable portion of the window wall system. A summary of field measurements on curtain wall envelopes are provided in Table 5 in descending mean ELA. Table 5. Airtightness Value of the Curtain Wall Façade from Previous Studies Reference Effective Leakage Area (ELA) (cm 2 /m 2 at 4 Pa) Comment Min Mean Max Persily, Not representative CMHC, Pre-retrofit values Tamura & Shaw, Used in Base Model CMHC, Post-retrofit values Jones et al., Buildings under WSEC/SEC requirements The values for curtain wall airtightness varied dramatically among different studies. Four office buildings with curtain wall systems were included in the first study. At the time of measurement, the average age of the buildings was more than 20 years, which could account for the mean leakage area being twice that of the next highest value in the table. The values in the last two rows of Table 5 were used in compartmentalization models, representing the air leakage rate when exterior airtightness was addressed. The ELA median of 1.32 cm 2 /m 2 was assumed for the model curtain wall system with no special effort to ensure airtightness. Table 6 contains exterior envelope components ELAs in the Base Model. 43

57 Table 6. Airtightness Inputs in Base Model Building Component Unit (ELA) Base Model Reference Balcony Door cm 2 /m 2 at 4 Pa 5.5 ASHRAE, 1997 Single Sliding Window cm 2 /m at 4 Pa 0.85 ASHRAE, 1997 Window Wall (fixed portion) cm 2 /m 2 at 4 Pa 1.32 Tamura & Shaw, Simulation Result Using the Base Model, the pressure distribution was simulated and plotted as shown in Figure 4. In the plot, the pressure of each zone is measured relative to the ambient pressure at the same elevation. The horizontal distance between two lines indicates the pressure difference between two zones. For instance, the pressure difference across the elevator doors could be read from the difference between the elevator line and the corridor line at any given floor. The neutral pressure plane (NPP) is the floor at which the inside and outside air pressure is the same, and is represented by the point at which each line crosses the zero zonal pressure line Base Model: Simulation Results Floor Number Zonal Pressure Relative to Ambient [Pa] North Stairwell Suite Elevator Corridor Figure 4. Simulated Pressure Difference in Base Model 44

58 Using the evaluation criteria, the base model performed poorly as summarized in Table 7, which was mainly due to the leaky building envelope. Although the HVAC system has been enlarged to four times its original size to account for the fourfold height, the system failed to overcome the stack-effect pressure differences. Therefore, an airtight building must be constructed to allow corridor pressurization system to function properly. Table 7. Simulation Results from Base Model Building Performance Contaminant Control Serviceability Suite Ventilation Total Air Infiltration Comment The corridor pressurization system failed to provide positive pressure relative to the suites from F1 to F14. Elevator door problem occurred on both upper and lower floors, with the maximum pressure difference around 50 Pa. Over ventilation problem occurred at the upper floors as up to 180 L/s per suite. Meanwhile, the suite located around neutral pressure plane hardly received any ventilated fresh air L/s outdoor air entered the building through the HVAC system, infiltration from suites, and the parking garage. The total energy required to condition the outdoor air to room temperature is noted as 100% Model SC1: Exterior Envelope Improvement The first step of suite compartmentalization was to improve the airtightness of the exterior envelope. This step was referred to as SC1 (see Table 4). An airtight building envelope could protect the tenant space from extreme weather events and reduce the energy loads due to uncontrolled air leakage Airtightness Inputs In this model, air leakage rates of building components located on the exterior façade were reduced in value to represent the improvement in the overall envelope airtightness. As shown in Table 8, the airtightness of balcony doors and windows were based on weather-stripping values suggested by ASHRAE fundamentals. For the fixed portion of the curtain wall, the attention to airtightness was represented by values from retrofitting programs or buildings located in the jurisdictions with whole building test requirements. 45

59 Table 8. Airtightness Inputs in Model SC1: Improving Exterior Envelope Building Component Unit (ELA) Base Model Model SC1 Reference Balcony Door cm 2 /m 2 at 4 Pa ASHRAE, 1997 Window cm 2 /m at 4 Pa ASHRAE, 1997 Fix Glazing Wall cm 2 /m 2 at 4 Pa Jones et al., 2014 Damper (closed) cm 2 /item at 4 Pa ASHRAE, 1997 Damper (open) cm 2 /item at 4 Pa ASHRAE, 1997 Exhaust dampers are not usually included in the envelope airtightness evaluation. As per ASTM E799, any intentional openings for HVAC purposes should be sealed or remain closed during the testing as they are not part of the air barrier design (ASTM, 2003). In reality, the backdraft damper can become a major leakage path especially when the room pressure is greater than the ambient pressure. One potential solution is interlocking the damper with the exhaust fan switch, so that the damper remains closed unless the exhaust fan is turned on. Simulations have shown that there was a significant improvement on the in-situ exterior airtightness associated with the installation of an interlocked exhaust damper Simulation Result The exterior envelope airtightness was improved from 3.35 L/s/m 2 at 75 Pa in the Base Model to 1.45 L/s/m 2 at 75 Pa (excluding exhaust dampers), which was less than the maximum air leakage requirement set by WSEC/SEC (2 L/s/m 2 at 75 Pa), as well as the definition of average airtight building by ASHRAE Fundamentals (Jones et al., 2014). One noticeable change in the pressure distribution plot shown in Figure 5 is that all of the pressure lines have moved to the right. A tighter exterior envelope allowed better building pressurization with the same HVAC system compared to the Base Model. Moreover, the pressure lines for each zone were together, which indicated that most of the stack pressure aggregated across the building façade. A thermal draft coefficient (TDC) value of 0.74 indicated that three-quarters of the stack pressure occurred across the exterior envelope. For residential buildings, the improvements achieved by an airtight envelope can be compromised by occupant behaviors, such as leaving the window or balcony doors open. 46

60 Improving Exterior Envelope (SC1): Simulation Results Floor Number Zonal Pressure Relative to Ambient [Pa] North Stairwell Suite Elevator Corridor Figure 5. Simulated Pressure Difference with Exterior Envelope Improvement (Model SC1) The evaluation of the building performance from Model SC1 is summarized in Table 9. Although there were improvements in all four categories compared to the Base Model, the problems induced by stack action were still not resolved yet. Table 9. Simulation Results from Model SC1: Improving Exterior Envelope Building Performance Contaminant Control Serviceability Suite Ventilation Total Air Infiltration Comment The corridor pressurization system failed to provide positive pressure relative to the suites from F1 to F7. Elevator door problem only existed for lower floors exceeding the threshold by up to 4 Pa. The pressure difference across the exterior openings increased up to 100 Pa. Slightly alleviated the over ventilation problem to 153 L/s per suite. However, not all the suite received a proper fresh air delivery rate. The total amount of air requiring conditioning decreased by 12% compared with the Base model, due to the reduction in uncontrolled airflow. 47

61 3.7.3 Model SC2: Suite Interior Improvement and HVAC Adjustments Other than the exterior envelope, suite compartmentalization also requires airtight construction of walls between the suite and the corridor, between adjacent suites, and at the connections to floor and ceiling slabs Airtightness Inputs Only changing the suite floor airtightness, the overall leakage rate of the typical suite (excluding HVAC openings) declined from 4.18 to 1.85 L/s/m 2 at 75 Pa. This suite leakage rate was slightly lower than the suggested compartmentalized suite value of 1.95 L/s/m 2 at 75 Pa (equivalent leakage calculated from LEED and Energy Star Multifamily High Rise program suggested rates of 1.5 L/s/m 2 at 50 Pa assuming n=0.65). However, the air from a typical suite could still bypass the airtight floor slab from the corridor, through the elevator shaft, then the corridor, and eventually to other suites. Therefore, both the vertical and horizontal separations of suites must be addressed to achieve effective suite compartmentalization. The airtightness values of the building components located at the interior partitions were increased based on values from past studies, as shown in Table 10. Table 10. Airtightness Inputs in Model SC2: Improving Suite Interior Partitions Building Model Model Unit (ELA) Component SC1 SC2 Reference Suite Door cm 2 /item at 4 Pa ASHRAE, 1997 Interior Wall cm 2 /m 2 at 4 Pa Shaw, Magee, & Rousseau, 1991 Suite floor cm 2 /m 2 at 4 Pa Shaw et al., HVAC Inputs Another adjustment to airtightness coupled with suite compartmentalization was the change in the HVAC system. In previous models, fresh air was delivered to each suite through undercut doors. After weather-stripping the suite doors, the majority of the corridor air would be redirected to the vertical shafts. Hence, another opportunity to promote energy efficiency was 48

62 downsizing the original HVAC system to accommodate corridor ventilation solely, while the suite ventilation could be provided by heat/energy recovery ventilators (HRV/ERV). A few assumptions were made in order to simulate the building behavior with the alternative HVAC system. First, it was assumed that the HRV units were mounted on the exterior envelope with great attention to airtightness. Therefore, no additional airflow occurred around the ventilator unit perimeter. Secondly, the HRV was assumed to be operated constantly at the rate of 40 L/s in every suite. The last assumption was that the HRV was able to provide the minimum heat recovery efficiency of 65% with the remaining 35% of the ventilation air required additional energy (AHRI Standard 1060, n.d.). In ASHRAE 62.1, the HVAC delivery rate for the corridor is supposed to be 0.3 L/s per m 2 floor area (ASHRAE, 2004). Therefore, in Model SC2, the total outdoor airflow required for corridor ventilation was set at 46.5 L/s per floor. Details for each ventilation supply grille can be found in Table 11. Table 11. HVAC Inputs in Model SC2: HVAC Adjustments Building Component Unit Model SC1 Model SC2 North HVAC L/s per floor Central HAVC L/s per floor South HVAC L/s per floor Total L/s per floor Simulation Results One of the changes in building pressure profile was the rise of the NPP of the elevator shaft from F12 in Model SC1 to F23 as shown in Figure 6. When the NPP is located near the middle floor of the building, the maximum stack pressure that can be developed is limited to half of the building height. With the movement of the NPP, the theoretical total stack effect pressure on F47 dropped from 134 Pa to 93 Pa. 49

63 Improving Interior Walls and HVAC (SC2): Simulation Results Floor Number Zonal Pressure Relative to Ambient [Pa] North Stairwell Suite Elevator Corridor Figure 6. Simulated Pressure with Interior Airtightness Improvement (Model SC2) Most evaluation criteria in Table 12 indicated that the building performance of Model SC2 improved with tighter interior partitions. Unfortunately, lower floors were not able to maintain a positive pressure difference from the corridor to each suite. It was because of the reduction in the corridor HVAC delivery rate that was made in Model SC2, which could result in contaminated air or smoke migration within the building. Therefore, additional effort was required to maintain a positive pressure differential across the suite doors on every floor. Table 12. Simulation Results from Model SC2: Improving Suite Interior Walls and HVAC System Building Performance Contaminant Control Serviceability Suite Ventilation Total Air Infiltration Comment The corridor pressurization system failed to provide positive pressure relative to the suites from F1 to F22. Pressure differences across elevator and stairwell door were within the allowance. Suite entrance doors and balcony doors were found to be difficult to operate. Most suites would had a proper air exchange rate through individual ventilators. Suites on a few top floors could experience over ventilation even when the HRV/ERV was not operating. The total amount of air requiring conditioning dropped to 57% compared with that from the Base Model. 50

64 3.7.4 Model FC1: Corridor Separation Improvement Instead of using excessive outdoor air, reducing the leakage area was an alternative approach to pressurize the corridor space with smaller amounts of air supply. Since the corridor-suite separation was fairly airtight, it was important to disconnect the corridor from the elevator and stairwell shafts by compartmentalizing each floor Airtightness Inputs When conducting the floor compartmentalization, it was assumed that the sealing details around the stairwell door perimeter, the airtightness of the corridor floors and the elevator shaft walls were the same as those of a compartmentalized suite. The significant improvement in elevator doors was based on the achievable targets for manufacturers suggested in the original report (CMHC, 1996). Details of the changed in Model FC1 are summarized in Table 13. Table 13. Airtightness Inputs in Model FC1: Improving Corridor Separations Building Component Unit (ELA) Model SC2 Model FC1 Reference Elevator Door cm 2 /item at 4 Pa CMHC, 1996 Stairwell Door cm 2 /item at 4 Pa ASHRAE, 1997 Corridor Floor cm 2 /m 2 at 4 Pa Shaw et al., 1991 Shaft Wall cm 2 /m 2 at 4 Pa Tamura & Shaw, Simulation Results The pressure distribution of Model FC1 shown in Figure 7 was similar to the outputs from Model SC2 except for the corridor pressure. Since the leakage area between the shaft and the corridor was reduced, most of the pressure differences were taken by the elevator shaft doors, thereby reducing the pressure differences across the suite entrance doors as well as the exterior envelope. 51

65 Improving Corridor Separation (FC1): Simulation Results Floor Number Zonal Pressure Relative to Ambient [Pa] North Stairwell Suite Elevator Corridor Figure 7. Simulated Pressure Difference with Corridor Separation Improvement (Model FC1) The greatest benefit from compartmentalizing the corridor was the reduction of uncontrolled airflows. The amount of airflow through envelope leakages in this model was half of the uncontrolled airflow in Model SC2 shown in Appendix C. Another advantage was the increase of corridor pressure difference relative to the suites on lower floors. However, Table 14 shows that the HVAC system was still incapable of developing sufficient pressure for contaminant control, which required a further improvement in the corridor airtightness. On the other hand, the current corridor airtightness had already led to an excessive pressure difference across the elevator shaft doors. Hence, the addition of a vestibule around the elevator lobby and stairwell doors could potentially increase the corridor pressure without introducing elevator door malfunction issues. 52

66 Table 14. Simulation Results from Model FC1: Improving Corridor Partitions Building Performance Contaminant Control Serviceability Indoor Air Quality Total Air Infiltration Comment The corridor pressurization system failed to provide positive pressure relative to the suites from F1 to F22. A mild pressure difference was across the suite and exterior walls. However, elevator and stairwell door problems occurred again. All suites would have a reliable air exchange rate with no over ventilation phenomenon. The total air conditioning loads were further reduced to 44%, benefiting from the reduction in uncontrolled infiltration Model FC2: Vestibule Installation and HVAC Adjustments Elevator vestibules could be placed throughout the entire building or only on those floors where excessive pressure differences occur. Installing vestibules on the problematic floors is more economical since it requires less material, labor, and a shorter construction schedule. In the first attempt, vestibules were installed on about half of the total building levels, F1-F14 and F41-F48, to maintain pressure differences across these elevator doors below 25 Pa. However, those floors with somewhat high stack pressures but no vestibule were vulnerable to the elevator door problems when the interior suite doors or exterior suite windows were opened. The mechanical system and wind pressures may also turn a non-problematic floor into a problematic one. Hence, all the floors should be equipped with elevator vestibules and additional vestibule doors should be installed where a great pressure difference exists at the stairwell shaft Airtightness Inputs It was assumed that there were two doors at the elevator vestibule and one door at the stairwell vestibule. The door leakage rate was the same as the suite entrance door with no additional leakage area around the vestibule perimeter. 53

67 HVAC Inputs The simulation result showed that even with the elevator vestibules, the HVAC airflow rate for ventilating the corridor areas was not sufficient to pressurize the hallway over the suites for floors below F20. Since the corridor was reasonably airtight, an additional step to realizing contaminant control was to increase the HVAC delivery rate for pressurization purposes. Raising the delivery rate ensured 5 to 10 Pa pressure difference from the hallway to the suites on every floor, with the HVAC airflow rate described in Table 15. Table 15. HVAC Inputs in Model FC2: Installing Vestibules and Increasing HVAC Airflow Rates Building Model FC1 Model FC2 Unit (ELA) Component F1 F12 F13 F24 F1 F12 F13 F24 North HVAC L/s per floor Central HVAC L/s per floor South HVAC L/s per floor Total L/s per floor Simulation Results Pressures of the elevator shaft lobby were included in the pressure distribution plot as shown in Figure 8. The horizontal distance between two zones suggested that most of the pressure differences occurred at the vestibule doors, whereas the pressure differences across the elevator doors, suite entrance doors and balcony doors were minor. Moreover, the pressure profile line of the corridor stayed to the right of the suite line on all floors, which mean that hallway pressures were greater than the suite pressures. The building performance analysis is further summarized in Table 16, showing that all the issues induced by stack action were resolved. 54

68 Installing Vestibules and HVAC (FC2): Simulation Results Floor Number Zonal Pressure Relative to Ambient [Pa] North Stairwell Suite Elevator Corridor Vestibule Figure 8. Simulated Pressure with Corridor Vestibules (Model FC2) Table 16. Simulation Results from Model FC2: Installing Vestibules Building Performance Contaminant Control Serviceability Suite Ventilation Total Air Infiltration Comment The corridor HVAC system was able to provide positive pressure difference on all floors except for F1, due to additional leakages to the parking garage. The pressure difference across all the doors has been limited to below operation threshold, except the vestibule doors. All suites would have a reliable air exchange rate with no over ventilation phenomenon. The total amount of air requiring conditioning energy was further reduced to 43% of that from the Base Model. Two important points from the simulation results should be noted. First, there was only a slight reduction in the total outdoor air entering the building from Model FC1 (44%) as shown in Table 14 to Model FC2 (43%) as shown in Table 16. By installing vestibules, the total uncontrolled air infiltration through leakage openings (building envelope and parking garage) dropped from 6161 L/s to 1583 L/s. However, there was about 4100 L/s more outdoor air going into the building through the HVAC system to increase the hallway pressure. The increased HVAC system offset the improvement in leakage control and diminished the overall advantage. 55

69 The second point was the serviceability of the vestibule doors. Being as the most airtight partition in the building, the vestibule door took the majority of the stack pressure differences, up to 87 Pa on F2. The excessive stack pressure was not reduced but instead transferred from the elevator doors to another building element. However, having most of the pressure differences across the vestibule door is preferred. It is more economical to install two motorized openers to help to open the vestibule door than motorizing every suite entrance door. Also, it is much easier to perform inspections and repair vestibule doors than elevator doors. Finally, the vestibule door might be less influenced by the occupant behavior and remain in the closed position since it is located in a common area Compartmentalization Steps Summary The building performance from all the compartmentalization strategies are shown in Figure 9, in accordance with the evaluation criteria. Compartmentalizing the suite perimeter only did not satisfy all of the performance requirements. It was very critical to address the airtightness of all the interior and exterior partitions as well as adjust the HVAC system accordingly. 56

70 Figure 9. Compartmentalization Steps: A Summary of the Model Responses The total outdoor air entering the building was gradually reduced with the increase in building airtightness, as shown in Figure 10. A promising improvement in the uncontrolled air leakage could also be observed from the plot, except for Model SC2 (suite compartmentalization with individual suite ventilator) where the reduction in the HVAC system raised the level of neutral pressure plane noticeably and led to additional infiltration. 57

71 Airflow Rate [L/s] Total Ambient Air Entering the Building Base SC1 SC2 FC1 FC Floor Number Airflow through HVAC Total incoming airflow Airflow through infiltration NPP of Elevator Shaft Figure 10. A Summary of Total Ambient Air Entering the Building from All Compartmentalization Steps 3.8 Parking Garage Compartmentalization In addition to the three compartmentalization strategies already discussed, another zone that can be isolated from the building is the underground parking garage. In the simulation model, the underground parking garage was connected to the rest of the building by the elevator and stairwell shafts. Air from the parking levels could migrate to upper floors via these pathways. Vestibules and a fan pressurization system were installed around the shafts in P1 and P2. The pressurization system was interlocked with CO detectors so that the fans remained off for the majority of the time. Furthermore, contaminated garage air could still enter the suites on the ground level through slabs, shown in the all the simulations. Therefore, compartmentalizing the parking levels could fundamentally eliminate the garage air from entering the building. 58

72 3.8.1 Approaches to Compartmentalizing Parking Garage There are two approaches to isolating the underground parking garage: vertical zoning and outdoor surface access. Instead of allowing direct access from parking to the residential floors, the first method implies separated elevator and stairwell shafts for the parking levels. Tenants would be required to take the garage elevator to the ground level, and then use another set of elevators to reach their destination floors. The first method reduces the amount of air that could be drawn from the garage through shafts, as well as the magnitude of stack effect. However, some contaminated air would still be able to enter the suites. In the second approach, the underground garage is isolated from the building by having the elevator and stairs exit outside at the ground level. Users must then enter the building as pedestrians to go to their floors. The second method was adopted in this research to investigate the maximum impact of parking garage compartmentalization. It was also assumed that additional sealing methods were applied to the floor slab between F1 and P1, so that the garage airflow though the floor slab was negligible (CMHC, 2007) Benefits of Compartmentalizing Parking Garage The separation of underground parking was applied to each simulation model included in the compartmentalization strategy analysis. The modelling identified the associated benefits, but also illustrated where the greatest improvement can occur. The detailed simulation results can be found in Appendix C. One of the significant findings was that disconnecting parking garage would not dramatically alter the building performance with respect to airflows and pressure differences. In all the models, only slight changes could be observed in the door pressure differences and the maximum suite ventilation rates. These changes were mainly due to the small changes in the location of NPP as shown in Figure

73 BuildingPerformance withgaragecompartmentalization Airflow Rate [L/s] Base Base+Garage SC1 SC1+Garage SC2 Floor Number SC2+Garage FC1 FC1+Garage FC2 FC2+Garage Airflow through HVAC Airflow through Infiltration Airflow through Parking Garage NPP of Elevator Shaft Figure 11. A Summary of Building Performance from All Compartmentalization Steps Compared the Results from Compartmentalizing Parking Garage The change in the location of NPP in the first 4 models (Base, SC1, SC2, and FC1) was only 1 floor. Since the elevator doors had greater leakage areas, reducing the openings on the parking levels did not significantly change the overall leakage area distribution of the elevator shaft. Hence, the theoretical stack pressure developed on the building remained almost the same. On the other hand, the location of NPP moved from F25 to F29 in Model FC2 when elevator vestibules were installed. However, the pressure differences across elevator and suite doors did not changed significantly because most of pressure changes were taken by the vestibule doors. Also worthy of note is the total air infiltration. There was only a 3% reduction in the total amount of ambient air entering the building throughout the simulation models. Theoretically, there would be a greater improvement from the early models where more air infiltration occurred at the garage before compartmentalization. However, the airflow through envelope leakage openings also increased when the NPP moved slightly upwards. For a leaky building envelope, the same magnitude of change in NPP would result in a greater air infiltration. Therefore, the net 60

74 effect of reducing garage inflow and introducing infiltration resulted in a 3% improvement in the total air infiltration by garage compartmentalization. 3.9 Conclusions Many performance issues occur in tall residential buildings because of the significant air pressure differences and airflows induced by stack effect. The knowledge gap existing in the literature is a lack of quantitative analysis pertaining to the effectiveness of compartmentalization. From the modelling used in the study presented here, the simulation results show that a compartmentalization strategy is effective in controlling contaminants, mitigating pressure differentials, providing reliable suite ventilation, and reducing the total amount of airflow that requires heating/cooling energy. The characteristics of each compartmentalization approach are illustrated by incrementally improving the building airtightness. Most of the requirements suggested by building codes and voluntary green building programs address the wall/slab airtightness around the suite perimeter. However, the suite level compartmentalization can only mitigate the building performance issues to some extent. Corridor spaces on each floor in a tall residential building must also be compartmentalized to reduce the likelihood of stack-induced problems. When the airtightness of the envelope is improved, the HVAC system requirements are reduced. The alteration in the HVAC system results in the neutral pressure plane located around the middle height of the building, which can avoid having large stack pressures occurring on the top or bottom levels. Also, the downsized HVAC system can reduce the capital investment and provide less but adequate fresh air to the building. This paper also discusses the fourth approach of compartmentalization, isolating parking garage levels. From the simulation, separating the parking garage would result in relatively localized improvements compared with compartmentalizing the entire 48-story building. However, it is essential to prevent contaminated garage air from entering the residential spaces for indoor air quality control. 61

75 Chapter 4 Full Compartmentalization Evaluation This chapter contains further details regarding the compartmentalization evaluation process. A tailored evaluation on the effectiveness of compartmentalization is discussed in Section 3.7 with a few key interim steps highlighted. In the following sections, a more comprehensive stepwise compartmentalization analysis is presented. This chapter reports all of the incremental improvement steps on building airtightness in detail. 4.1 Compartmentalization steps During the evaluation process of compartmentalization strategies, 9 models (Model A-H) were constructed in order to reflect the incremental benefits of improving the building airtightness. From those 9 models, 5 models which represented as the key compartmentalization steps are discussed in Chapter 3.7. A list of all the compartmentalization interim steps as well as their descriptions is shown in Table 17. Table 17. Computer Simulation Steps in Evaluating Compartmentalization Approaches Approach Step Name Description In Chapter 3 No Base No special attention made on 1 Base Model Compartmentalization Model airtightness 2 Model A Exterior envelope improvement - Suite Compartmentalization 3 Model B Interlock exhaust damper Model SC1 4 Model C Suite floor slab improvement - 5 Model D Suite demising wall improvement - 6 Model E Suite individual ventilation Model SC2 7 Model F Corridor separation improvement Model FC1 Full Compartmentalization 8 Model G Vestibule installation - 9 Model H Corridor HVAC adjustment Model FC2 62

76 The first key compartmentalization step was improving the exterior envelope airtightness, which was highlighted as Model SC1 previously. In this chapter, the process of addressing building façade was further divided into two steps (Model A and B). Model A emphasized sealing the leakage openings around building components such as balcony doors, windows. In the next step, Model B, changes were made to the HVAC system by interlocking the backdraft dampers in the exhaust system to improve airtightness even further. The second key compartmentalization step was improving the interior partitions around the suite perimeters, denoted as Model SC2. There were three interim steps (Model C, D, and E) from constructing airtight building envelope (Model SC1) to implementing suite compartmentalization (Model SC2). The purpose of Model C, D, and E was to provide an in-depth understanding of the effectiveness in the building performance when different interior partition walls and the HVAC system were altered. In the full compartmentalization strategy, the airtightness around the corridor perimeter was addressed. Firstly, airtightness of the corridor components (doors, floor slabs, shaft walls) were improved to the minimum values suggested from the literature in Model F (Model FC1). Then the benefits of installing vestibules at the elevator lobby on every floor were assessed in Model G. Last but not least, the HVAC system for the corridor area was further adjusted to pressurize the hallway to the desired level, and the results were shown in Model H (Model FC2). 4.2 Compartmentalization Steps Summary This section provides a summary of the building performance from each compartmentalization step as well as significant research findings. The details of the simulation inputs and pressure distribution outputs can be found in Appendix D. The building performance from all the compartmentalization strategy simulations is tabulated in Figure 12 in accordance with the evaluation criteria. In conclusion, a full set of compartmentalization strategies (from Base Model to Model H) along with adjustments in the 63

77 HVAC system should be applied to mitigate the building performance issues induced by stack action. Figure 12. A Summary of Building Performance from All Compartmentalization Steps The total outdoor air entering the building has been gradually reduced with the increase in building airtightness, shown in Figure 22. A promising improvement on the uncontrolled air leakage could also be observed from the plot, except for Model E where the reduction in HVAC system raised the level of neutral pressure plane noticeably and led to additional infiltration. 64

78 Airflow Rate [L/s] Base Model Total Ambient Air Entering the Building Model A Model B Model C Model D Model E Model F Model G Model H Floor Number Airflow through HVAC Total incoming airflow Airflow through infiltration NPP of Elevator Shaft Figure 13. A Summary of Total Ambient Air Entering the Building from All Compartmentalization Steps 65

79 Chapter 5 Closing Chapter Increasing building height improves urban land use and energy consumption efficiency, but it exacerbates some challenges that could affect the building performance. Stack effect, for instance, is a phenomenon that exists in all buildings, but has much greater adverse impacts on tall buildings. This research aims at investigating the critical issues induced by stack action and providing recommendations on the mitigation strategy to be implemented in tall residential buildings. The first objective was to examine current mitigation approaches to reduce stack-action induced issues. Several mitigation strategies were proposed in the literature, including using the building mechanical system (active) or installing entry vestibules to reduce the excessive pressures and airflows induced by stack effect (passive). However, these solutions might not be very effective due to the complexities of tall residential buildings such as the rapidly changing ambient environment, secondary issues induced by implementing localized solutions, and the effect of occupant behavior. Compartmentalization is a passive mitigation strategy that proposes to disconnect the airflow exchange by creating multiple airtight barriers around the perimeter of each zone in the building. The isolation of building elements could redistribute pressures and reduce airflows across building zones. Compartmentalization could also provide a resilient solution in that the effects of occupant behavior, such as opening windows or doors, are mitigated by the multiple layers of airtightness that compartmentalization provides. Hereby, compartmentalization could be a promising passive strategy for combating the adverse effects caused by stack effect. This was discussed in Chapter 2. Given the results from the first objective, the second objective of this research was to evaluate the effectiveness of compartmentalization. Very little information was available in the literature about the actual benefits of implementing this strategy in tall residential buildings. The reasons for the insufficient field measurement data mainly resulted from the lack of a proper airtightness 66

80 testing method for multi-zone structures, a uniform airtightness metric for direct comparisons, and clearly documented information of the tested buildings. The second part of the research focused on quantifying the effectiveness of compartmentalizing a building using computer simulation. During the simulation process, a compartmentalization strategy was implemented on a case building to illustrate the advantages of improving building airtightness. The simulation results showed that compartmentalization was capable of maintaining a higher pressure level in the corridors for contamination control, reducing the magnitude of pressure differentials across internal doors to improve building serviceability, ensuring a proper ventilation rate in all the suites, and cutting by more than 50% the total volume of incoming ambient air. In addition to examining the overall advantages of compartmentalizing a building, the effectiveness of different compartmentalization approaches was simulated and discussed. Suiteby-suite compartmentalization was deemed as the most cost-effective method in the literature. Some of the requirements in building codes and voluntary green building guidelines provide limits for airtightness around a suite perimeter, but floor-by-floor compartmentalization and the separation between the corridor and vertical shafts received much less attention. The incremental step results from the simulation illustrated that improving the airtightness around the suite perimeter was able to reduce building serviceability issues and the total air leakage rate to a good extent, but it could not eliminate the problems in contamination control and suite overventilation. Therefore, the separation between floors is equally critical in a multi-zone structure. Another question was whether implementing floor-by-floor compartmentalization would be sufficient in a tall residential building. Although installing corridor vestibules and improving slab airtightness could resolve most of the building performance problems, a full compartmentalization (both suite and floor level) is still highly recommended. The essential concept of compartmentalization is creating redundancy in the air barrier so that if the tenant breaks one layer of the air barrier by opening windows or doors, a secondary layer would be able to provide airflow resistance and minimize the impact on the other building zones. It was mentioned in the early sections that exterior windows were found open even during cold winter 67

81 nights; in this case, the corridor vestibule became the primary air barrier. Implementing floor-byfloor compartmentalization alone could subject the building to the occupant behavior; therefore, a full compartmentalization is necessary to ensure its effectiveness in reducing stack-action induced problems. Parking garage compartmentalization was also discussed in this research. It should be noted that isolating the parking garage resulted in localized improvements only. Since the airtightness improvement in the parking garage was smaller than the changes in the entire building, the pressure and airflow changes were minor compared to the other compartmentalization approaches. But garage isolation is important to stop contaminated air migration from the parking garage to residential floors. To achieve compartmentalization, attention to the sealing details around the assembly connections must be paid. Although this research mainly focuses on the performance results of mitigating stack-action induced problems, the degree of airtightness in the simulation is achievable using currently available technologies and practices. Firstly, the airtightness values used in computer simulation were collected from existing field measurements. Most of them were the best-estimates or minimum airtightness values from ASHRAE Fundamentals 1997, which means the current construction method should be able to achieve the required airtightness level. Secondly, some airtightness tests conducted on existing buildings has shown an equal or better result. One study in 2006 tested two suites under suite level compartmentalization in a residential building (Hill, 2006). Spray-applied polyurethane foam or sheet polyethylene was used for the exterior system, while the interior airtightness was addressed using an airtight drywall approach to form a continuous airtight barrier. The field test results showed that the overall leakage rate of the two suites were 0.42 and 0.68 L/s/m 2 at 75 Pa, which is better than the airtightness result of 0.76 L/s/m 2 at 75 Pa from the simulation model. Last but not least, a survey was conducted in the State of Washington to collect industry feedback on the mandatory requirement of the whole building airtightness (RDH, 2015). Among the results collected from 19 respondents (architecture, engineering, construction, owner, and testing agency), 84% suggested that the airtightness testing was beneficial and worthwhile, and 95% agreed that there was low to moderate cost involved to achieve the whole building airtightness requirement. 68

82 Although there is little direct field evidence supporting the achievability and feasibly of compartmentalization, the design and construction experience with building airtightness suggest that it is possible to construct a building with a desired compartmentalization level at a reasonable cost. There are a number of limitations in this research. The quality of the simulation results could be improved if these limitations are addressed in the future. a) The first set of limitations are simulation software related. The simulation program used in this project, CONTAM, assumes that the air in each building zone is perfectly mixed, and no airflow travels within the boundary between two zones (wall cavity). b) Since little field measurement was conducted on existing tall residential buildings, the simulation model was construed based on a 12-story MURB and then was expanded to a 48-story residential tower, under the assumption that the typical residential floor layout remained the same. c) In the calibration process, a few assumptions were made as the model inputs. For instance, the indoor air temperature was assumed to be 20 C for all the building zones, and the HVAC system was assumed to be operated under the design flow rate. Although there were 19 sets of field measurement data on the pressure distribution, only one set of data with trimmed values were used as the calibration reference. d) Last but not least, the analysis of the effectiveness of compartmentalization was based on computer simulation results. The actual performance of this strategy should be assessed and verified by conducting field tests on tall residential building with compartmentalization implemented. There are many opportunities to expand on this research in the future. The evaluation of the effectiveness of compartmentalization was carried out mainly upon the computer simulation. Those simulation results could deviate from the actual stack pressures and airflows due to the limitations of the software and simulation assumptions. Compartmentalizing a tall residential building and completing field test experiments on the airtightness value as well as building performance would be of great value. Prior to the field application, a guideline of conducting airtightness measurement in multiunit residential buildings should be developed. The test 69

83 protocol could be based on the suite/floor level blower test mentioned in Section 2.6.1, but the problem such as limited airtightness results must be addressed. As more applications of compartmentalization being tested and the effectiveness being confirmed, the field measurement database would be beneficial for evaluating the current building design codes and develop a sufficient airtightness standard for tall residential buildings. The contributions of this research help propose one promising solution to the problems occurred in tall residential buildings, quantitatively evaluate the effectiveness of compartmentalization, and identify the roadmap for implementing this strategy. 70

84 References AHRI Standard (n.d.). Performance Rating of Air-to-Air Heat Exchangers for Energy Recovery Ventilation Equipment. Air Conditioning and Refrigeration Institute. ASHRAE. (1997). ASHRAE Handbook 1997 (Vol. Chapter 25, Table 3). ASHRAE. (n.d.). TC 9.12 Tall Buildings. Retrieved September 1, 2017, from building-applications/tc-9-12-tall-buildings ASHRAE, A. (2004). ASHRAE Ventilation for Acceptable Indoor Air Quality. Atlanta, GA. ASTM. (2003). ASTM E Standard Test Method for Determining Air Leakage Rate by Fan Pressurization. ASTM International. Best, R., & Demers, D. (1982). Investigation Report on the MGM Grand Hotel Fire, Las Vegas, Nevada, November 21, National Fire Protection Association. BHMA. (2000). A American National Standard for Door Controls - Closers. Inc.; 2000 (ANSI/BHMA A156. 4). Bohac, D. L., Fitzgerald, J. E., Hewett, M. J., & Grimsrud, D. (2007). Measured Change in Multifamily Unit Air Leakage and Airflow Due to Air Sealing and Ventilation Treatments. In Proc. Buildings X: Thermal Performance of the Exterior Envelopes of Whole Buildings. Clearwater, Florida, USA. Builders Hardware Manufacturers Association. (2013, May 28). ANSI/BHMA A156.4 Door Controls-Closers. 71

85 CAN/CGSB. (1986). CAN/CGSB M86: Determination of the Airtightness of Building Envelopes by the Fan Depressurization Method. City of Toronto. (n.d.). Door Closer - Apartment Doors. Retrieved March 25, 2018, from CMHC. (1996). Controlling Stack Pressure in High-rise Buildings by Compartmenting the Building (No. CA1 MH65 96C57). Canada Mortgage and Housing Corporation. CMHC. (2001). Air Leakage Characteristics, Test Methods and Specifications for Large Buildings (No. CA1 MH 01A34). Canada Mortgage and Housing Corporation. CMHC. (2005). Assessment of Suite Compartmentalization and Depressurization in New High- Rise Residential Buildings (No. CA1 MH 05A77). Canada Mortgage and Housing Corporation. CMHC. (2007). Airtightness of Concrete Basement Slabs (No ). Canada Mortgage and Housing Corporation. CMHC. (2017). Air Leakage Control for Multi-Unit Residential Buildings (No. ISBN pdf CTBUH. (2017). CTBUH Height Criteria. Retrieved September 1, 2017, from ). Retrieved from ftp://ftp.cmhc-schl.gc.ca/chic-ccdh/pamphletsopims/65847_ CRP Securities. (n.d.). Installation Instructions Series Door Closer. Retrieved from Closers%20ver.%202_.pdf GB/Default.aspx 72

86 Department of Justice. (2010, September 15) ADA Standards for Accessible Design. Dols, W. S., & Polidoro, B. J. (2015). CONTAM User Guide and Program Documentation Version 3.2. Elevator Traffic Planning. (n.d.). Retrieved March 9, 2018, from Finch, G., Burnett, E., & Knowles, W. (2009). Energy consumption in mid and high rise residential buildings in British Columbia (pp ). Presented at the 12th Canadian Conference on Building Science and Technology, Montreal, Quebec, Canada. Finch, G., Straube, J., & Genge, C. (2009). Air Leakage Within Multi-unit Residential Buildings: Testing and Implications for Building Performance. In 12th Canadian Conference on Building Science and Technology (pp ). Montreal, Quebec, Canada. Gulay, B. W., Stewart, C. D., & Foley, G. J. (1993). Field Investigation Survey Summary Report of Air Tightness, Air movement, and Indoor Air Quality in High-rise Apartment Buildings in Five Canadian Regions : Report to CMHC (No. CA1 MH65 93F33). Canada Mortgage and Housing Corporation. Retrieved from ftp://ftp.cmhc-schl.gc.ca/chic-ccdh/research_reports- Rapports_de_recherche/Older4/Ca1%20MH65%2093F33%20(w).pdf Hill, D. (2006). Evaluation of Air Leakage Control Measures to Compartmentalize Newly Constructed Suites in a High-Rise Residential Building (No. CA1 MH110 06E81). CMHC. Retrieved from ftp://ftp.cmhc-schl.gc.ca/chic-ccdh/research_reports- Rapports_de_recherche/eng_unilingual/Evaluationofairleakage.pdf Hutcheon, N. B., & Handegord, G. O. (1994). Building Science for A Cold Climate. Jo, J.-H., Lim, J.-H., Song, S.-Y., Yeo, M.-S., & Kim, K.-W. (2007). Characteristics of Pressure Distribution and Solution to the Problems Caused by Stack Effect in High-rise Residential Buildings. Building and Environment, 42(1),

87 Jones, D., Brown, B., Thompson, T., & Finch, G. (2014). Building Enclosure Airtightness Testing in Washington State-Lessons Learned about Air Barrier Systems and Large Building Testing Procedures. Presented at the 2014 ASHRAE Annual Conference, Seattle, WA. Kayll, D. G., Torok, G. R., & Jutras, R. (2017). NBC 2015 Subsection Other Fenestration Assemblies - The Intent Behind the New Code Provisions. Presented at the 15th Canadian Conference on Building Science and Technology, Vancouver, BC, Canada. Klocke, S., Faakye, O., & Puttagunta, S. (2014). Challenges of Achieving 2012 IECC Air Sealing Requirements in Multifamily Dwellings. United States. Department of Energy. Office of Energy Efficiency and Renewable Energy. Klote, J. H. (2015). MGM Grand Fire And Fire Safety Then, Now. ASHRAE Journal, 57(11), Koo, S.-H., Jo, J.-H., Seo, H.-S., Yeo, M.-S., & Kim, K.-W. (2004). Influence of Architectural Elements on Stack Effect Problems ub Tall Residential Building. Presented at the CTBUH 2004 Seoul Conference, Seoul, Korea. Lee, J., Hwang, T., Song, D., & Kim, J. T. (2012). Quantitative Reduction Method of Draft in High-Rise Buildings, Using Revolving Doors. Indoor and Built Environment, 21(1), Levin, P. (1988). Air leakage between apartments. In 9th AIVC Conference Effective ventilation. Ghent, Belgium. Li, J., McCabe, B., Pressnail, K., & Shahi, A. (2018). Compartmentalization as a solution to managing stack effect in tall residential buildings. Presented at the 4th Residential Building Design & Construction Conference, State College, PA, USA. Lovatt, J. E., & Wilson, A. G. (1994). Stack effect in tall buildings. ASHRAE Transactions, 100(2),

88 National Building Code. (2010). Associate Committee on the National Building Code, National Research Council. Ontaio Fire Code. (2018, March 18). Retrieved March 25, 2018, from Ontario Building Code. (2015). Retrieved March 9, 2018, from Orme, M., Liddament, M. W., & Wilson, A. (1998). Numerical data for air infiltration and natural ventilation calculations. Air Infiltration and Ventilation Centre. Palmiter, L., Heller, J., & Sherman, M. (1995). Measured Airflows in A Multifamily Building. ASTM Special Technical Publication, (1255), Persily, A. K. (1998). Airtightness of commercial and institutional buildings: blowing holes in the myth of tight buildings. Building and Fire Research Laboratory, National Institute of Standards and Technology. Proskiw, G., & Phillips, B. (2008). An Examination of Air Pressure and Air Movement Patterns in Multi-Unit Residential Buildings. In Building Enclosure Science and Technology (BEST) Conference (pp ). RDH. (2013). Air Leakage Control in Multi- Unit Residential Buildings, Development of Testing and Measurement Strategies to Quantify Air Leakage in MURBS (No ). RDH Building Engineering Ltd. Retrieved from Control-in-Multi-Unit-Residential-Buildings.pdf RDH. (2015). Study of Part 3 Building Airtighness (No ). RDH Building Engineering Ltd. Retrieved from Testing-and-Results-Report.pdf 75

89 Reardon, J. T., & Shaw, C. Y. (1988). Balanced Fan Depressurization Method for Measuring Component and Overall Air Leakage in Single-and Multifamily Dwellings. Air Infiltration Review, 9(4), 7 8. Red River College. (2015). Airtightness in Existing Multi-Unit Residential Buildings: Field Trials of a New Test Protocol. Red River College Applied Research and Commercialization Sustainable Infrastructure Technology Research Group. Retrieved from Ricketts, Lorne. (2014, January 23). A Field Study of Airflow in a High-Rise Multi-Unit Residential Building. University of Waterloo, Waterloo, Ontario, Canada. Ricketts, L., & Straube, J. (2014). Corridor Pressurization System Performance in Multi-Unit Residential Buildings. Presented at the 2014 ASHRAE Annual Conference, Seattle, WA. Shaw, C. Y. (1980). Methods for Conducting Small-scale Pressurization Tests and Air Leakage Data of Multi-storey Apartment Buildings. ASHRAE Transactions, 86(1), Shaw, C. Y., Magee, R. J., & Rousseau, J. (1991). Overall and component airtightness values of a five-story apartment building. ASHRAE Transactions, 97, Part 2, Sherman, M. H., & Chan, W. R. (2006). Building air tightness: research and practice. Building Ventilation: The State of the Art, Song, D., Lim, H., Lee, J., & Seo, J. (2014). Application of the mechanical ventilation in elevator shaft space to mitigate stack effect under operation stage in high-rise buildings. Indoor and Built Environment, 23(1), Straube, John. (2014). Airtightness Testing in Large Buildings (No. BSD-040). Building Science Corporation. Retrieved from

90 airtightness-testing-in-large-buildings Tamblyn, R. T. (1991). Coping with Air Pressure Problems in Tall Buildings. ASHRAE Transactions, 97(1), Tamblyn, R. T. (1993). HVAC System Effects for Tall Buildings. ASHRAE Transactions, 99(2), Tamura, G. T., & Shaw, C. Y. (1976). Air leakage data for the design of elevator and stair shaft pressurization systems. ASHRAE Transactions, 82(2), Tamura, G. T., & Wilson, A. G. (1968). Pressure Differences Caused by Chimney Effect in Three High Buildings and Building Pressures Caused by Chimney Action and Mechanical Ventilation. ASHRAE Transactions, 73(2), II 1. Tamura, T. G., & Shaw, C. Y. (1976). Studies on exterior wall airtightness and air infiltration of tall buildings. ASHRAE Transactions, 82, Part 1, Ueno, K., & Lstiburek, J. W. (2015). Field Testing of Compartmentalization Methods for Multifamily Construction. United States. Department of Energy. Office of Energy Efficiency and Renewable Energy. Urquhart, R., Richman, R., & Finch, G. (2015). The effect of an enclosure retrofit on air leakage rates for a multi-unit residential case-study building. Energy and Buildings, 86, Yale. (n.d.). Hold Open Door Closers - Installation Instructions. Retrieved from 77

91 Appendix A. Calibration Appendix A contains details of the simulation calibration process that supplement information in Chapter 3. Simulation results after calibration are mentioned in Section 3.5. Additional details in regard to the simulation software, field measurement selection, calibration process, and airtightness inputs in the calibrated model are discussed in the following sections as shown in Figure 14. Simulation Software Field Measurement Selection Calibration Process Airtightness Inputs Figure 14. Calibration Process In the simulation software section, the differences between the old CONTAM program used in the original case study and the latest version are identified, as well as the consequential improvements in the simulation outputs. Then the field measurement selection section reviews the quality of the measurements collected from field tests. During the calibration process, factorial analysis was used to determine the best combination of the leakage characteristics for each building component. However, the poor estimated pressure results suggested that additional leakage paths should be included in the simulation. After achieving a good presentation of the pressure behavior in the case building, the airtightness inputs included in the calibrated model was examined against the values suggested in past studies. 7.1 Simulation Software: CONTAM93 and CONTAM3.2 Computer simulation was conducted in the original case study to evaluate the benefits of compartmentalization. The simulation program named CONTAM93 was used to produce pressure and airflow results of the case building. Continuously developed by Nation Institute of Science and Technology (NIST), CONTAM3.2 was the latest simulation software available and was adopted in this research project (Dols & Polidoro, 2015). The essential algorithm of the two 78

92 software are based on fluid dynamics principles. Whereas, a few additional features implemented in COMTAM3.2 are able to address the simulation issues of CONTAM93 flagged in the original report (CMHC, 1996) Backdraft Damper In CONTAM93, the leakage area of suite exhausts was assumed to be equivalent to a hole on the exterior façade. In reality, backdraft dampers are usually installed in the exhaust system to control the airflow direction. For instance, indoor suite air is able to flow through the damper towards the outside when the suite pressure is greater than the ambient pressure. However, when the ambient pressure is higher, the backdraft damper would remain closed to prevent air from entering the suite. For the lower portion of a building where it is often subjected to air infiltration during heating seasons, the amount of airflow across the building envelope can be significantly reduced by implementing backdraft dampers. One of the improvements in CONTAM3.2 is the feature of simulating backdraft dampers, which allows to generate a more realistic airflow network result HVAC System The second difficulty using CONTAM93 is simulating the performance of the HVAC system. In the original study, the HVAC system was simulated using vertical shafts (similar to the elevator shaft) which connect the air handling unit on the roof to the corridor space on each floor. However, resulted from this approach, the simulated HVAC delivery rate at the supply grille on each floor was not evenly distributed throughout the building. In reality, a damper is commonly applied prior to the supply grille to overcome the stack pressure and control the air delivery rate. Duct balance is another feature incorporated in CONTAM3.2 that allows the simulation to automatically adjust the HVAC ductworks to the design flow rate. 79

93 7.2 Data Selection Field test was conducted in the original study, measuring the pressure difference between the zone of interest and the north stairwell. Those measurement points were used to calibrate the model and evaluate the quality of the simulation results. Although 19 sets of measurements were carried out, the model was calibrated to only one measurement set in which the conditions represented no wind, HVAC system operating, and all doors closed, as mentioned in Section The field testing results are tabulated in Table 18 (CMHC, 1996). Within the one set of data, the measured pressure differentials were further selected and a few data points were discarded from the calibration process. Table 18. Field Measurement Results Collected with No Wind, HVAC System Operating, and All Doors Closed Location Point Measured Pressure Difference [Pa] Roof Roof -49 Elevator Mechanical Room -30 Elevator Shaft 3 Corridor th Floor Garbage Room -8 Unit Unit North Supply Vent -11 North Corridor 6 Lobby Vestibule 4.9 Ground Floor Main Lobby (by Elevator) 4.6 North Supply Vent 8.4 Unit Unit Parking Level 1 Garage 6.9 Garbage Chute Shaft Ambient Outside E.Side 6.1 Pressure Reference North Stairwell at 12 th Floor North Stairwell at 1 st Floor Roof & Elevator Machine Room Illustrated from methodology in the original study, pressure taps and tubing were used to measure the zonal pressure in regard to the north stairwell with one micronanometer at the 80

94 ground level and another one at F12. This approach could produce reliable results where the measured zone was located on the same floor as the micromanometer level. However, experimental errors might be introduced when the two measured zones were on different levels. Taking the roof as an example, the value at the roof was recorded as -49 Pa, which meant the ambient pressure at the roof level was 49 Pa lower than the pressure in the north stairwell at F12 under the assumption that the micromanometer was located at F12. If it was assumed that the ambient pressure at the ground level was Pa as the standard condition, the outdoor air temperature was C, and the elevation of roof was 31.8 m, then the ambient pressure on the roof level was calculated to be Pa, using ΔP = ρgh. In accordance with the roof measurement value, the absolute pressure of the north stairwell at F12 was Pa. Since it was also recorded that the pressure difference at the outside ground floor was 6.1 Pa, the absolute pressure of the north stairwell at F1 would be Pa. Therefore, the total pressure change in the north stairwell from F1 to F12 was 367 Pa in regard to the field measurement results. On the other hand, the theoretical pressure change along the stairwell shaft could also be estimated using ΔP = ρgh, which was calculated to be 344 Pa assuming the indoor air temperature was 20 C and the height between F1 and F12 was m. As the result, there was a 23 Pa inconsistency between the field measurement and the theoretical pressure change in the stairwell shaft. The calculation results are included in Table 19. Table 19. Absolute Pressure of Various Location Calculated from the Measurement Data Location North Stairwell [Pa] Ambient [Pa] Suite 1212 [Pa] Roof th Floor Ground Floor Moreover, the absolute pressure of the suite located on F12 could be deduced from the field measurements as well. The measured pressure difference between the suite 1212 and north stairwell at F12 was -17 Pa, so that the absolute pressure of suite 1212 was calculated as Pa. On the other hand, the absolute ambient pressure at F12 was estimated to be Pa using ΔP = ρgh, assuming the outdoor air temperature was C and the height between F1 and F12 was m. Indicating from the calculation, the ambient pressure was greater than the suite 81

95 pressure, which would lead to outdoor air entering the building. However, when a building is under the stack effect and corridor pressurization system, the zonal pressure of the suite on the higher levels should be greater than the ambient and force the room air to flow across the envelope towards the outside. Because no further information of conducting pressure tests with zones located on different levels was provided in the original study, the measured value of roof was no longer being used in the calibration process. It was due to the same reason that elevator machine room was removed from the list as well Garage & Garbage Chute Shaft The measurements of the garage and garbage chute shaft were subjected to the same experimental issues as mentioned above. However, it was found that the pressure differences of these two zones could be measured with respect to the north stairwell shaft at the parking level P Supply Vent on F1 & F12 The pressure difference between the north ventilation grille and the north stairwell at F12 was measured as -11 Pa. However, the field result of the corridor at F12 was -7 Pa, which implied that the pressure in the hallway was greater than the pressure in the HVAC supply grille. In reality, the pressure in the HVAC supply duct must be greater in order to deliver fresh air to the corridor. No additional details regarding the procedures for measuring HVAC supply grille pressure were provided in the original report. Hereby, the data points related to supply vent were not considered in the calibration process. 82

96 7.2.4 Suite Four suites were measured in the building: 103, 111, 1202, and But the suites were noted as NE1, NE2, and SE1 etc. in the simulation model. Since it was unclear about the relationship between the suite number and its location in the building, an alternative pressure difference was used by averaging the results from the two suites on the same floor. Correspondingly, an averaged simulation result would be used in comparison to the measurements, which was the average of pressure differences of all the suites located at F1 and F Calibration Process Factorial analysis was used in the first attempt of calibrating the model. First, a list of building components was identified as variables, such as elevator doors, windows, exterior envelope, and partition walls etc. For each variable, three airtightness values (minimum, best estimation, and maximum) were determined from the literature. Then another computer software, ContamFactorial, was used to generate a series of building models containing all the combinations of different airtightness values for each variable. As the result, the model with the least difference between the simulation values and the field measurements was selected as the best-calibrated model. However, the selected model with the smallest estimation error was not able to simulate the pressure distribution in the building very well. It was observed that the airtightness inputs for most variables might exceed the max/min values in order to produce a better pressure prediction. The error between simulation results and measurements indicated that some airflow paths might not be captured in the original model. Review of the original case study report suggested that the leakage areas in the parking level such as transformer ventilation grilles, emergency generator intakes, and exhaust dampers were significantly greater than the values defined in the CONTAM model. Moreover, the simulation results from the first run indicated that additional airflow paths might exist between the parking level and the ground lobby, as well as between the 12 th floor corridor and the roof. Those additional leakage spots could result from penetrations of the piping system and HVAC 83

97 ductworks. Once these leakage areas were redefined, the simulation results started to converge to the measurements with reasonable airtightness values applied. Compared with walls and floor slabs, doors are the greatest contributor to airflow path within a building. Elevator doors and four types of hinged doors were defined in the original study. Although the door leakage rates documented in the study were much leakier than the values suggested by ASHRAE fundamentals, those values were collected from field tests. Hereby, the values from the original study were used in the calibration process shown in Table 20, and the tighter ASHRAE numbers were adopted in the compartmentalization analysis. Table 20. Leakage Values of Doors from Field Tests and Literature Variable Name Unit Calibrated Model Airtightness [ELA at 4 Pa] Best Min Estimate Max Reference Elevator cm Door 2 Tamura & /item Shaw, 1976 Leaky Door cm 2 /item Standard cm Door 2 Tamura & /item * - 188* Shaw, 1976 Tight Door cm 2 ASHRAE, /item ** 33** 78** 1997 Weatherstripped Door 2 ASHRAE, cm /item ** 24** 52** 1997 Note: * These values are collected from conducting field testing on the stairwell doors in 8 office buildings. In the original simulation model, standard doors were used at the stairwell shaft. ** The air leakage around the door frame is included in these values accordingly. For instance, the best estimate leakage area of the tight door is calculated by adding the best estimated door frame leakage to the best estimated door value. 7.4 Calibration Result The details of simulated pressures from the calibrated model are discussed in Section With one exception on elevator shaft (2.5 Pa), the calibrated model estimated the pressure difference at each measuring point to within ±1.0 Pa of the field measurements. Therefore, it could be stated 84

98 that the calibrated model was able to provide a good simulation of the stack effect in reality. The airtightness of individual variable (building component) used in the calibrated model is tabulated in Table 21, with the comparison to the suggested values from the literature. Table 21. Airtightness of Building Components Used in the Calibrated Model and Suggested from the Literature Variable Unit Airtightness [ELA at 4 Pa] Calibrated Best Min Model Estimate Max Interior Wall cm 2 /m Reference Shaw, Magee, & Rousseau, 1991 Exterior Wall cm 2 /m Persily, 1998 Window cm 2 /m ASHRAE, 1997 Exhaust Vent (damper closed) Exhaust Vent (damper open) cm 2 /item ASHRAE, 1997 cm 2 /item ASHRAE, 1997 Floor (Corridor) cm 2 /m Floor (Suite) cm 2 /m Shaft wall cm 2 /m Roof cm 2 /m Shaw et al., 199) Shaw et al., 1991 Tamura & Shaw, 1976 Orme, Liddament, & Wilson, 1998 As it could be observed from the table, the majority of the leakage rates were within the suggested ranges. However, a few building components exceeding the airtightness ranges required additional justification. For exterior walls, the airtightness in the calibrated model was significantly tighter than the reference by one order of magnitude. Although the values in the reference were associated with frame/masonry exterior walls, the data were collected from commercial buildings (retails, schools, and industrial) with ages from newly constructed to over 40 years. The type and age of the buildings included in that study might result in a much leakier envelope than that from multifamily residential buildings. Instead of examining the exterior wall assembly only, the overall airtightness of the exterior envelope could be used to evaluate the quality of the simulation inputs. Two studies had conducted field testing on frame/masonry 85

99 façade of residential buildings, and the measured overall airtightness values were 2.28 and 2.04 L/s/m 2 at 75 Pa correspondingly. The total air leakage rate combining the exterior walls and windows from the simulation was 1.89 L/s/m 2 at 75 Pa, which was close to the two field measurements. The airtightness of the slabs for both the suite and the corridor, as well as the roof, fell out of the range suggested by the past studies. It was found that, during the calibration process, the changes made on those horizontal separations did not significantly affect the simulation results. A sensitivity analysis was conducted to further illustrate the relative changes in the simulation outputs by altering the airtightness of individual building component, shown in Table 22. When testing the sensitivity of one variable, its airtightness was reduced by 30% (raised 30% if the value was the less than the minimum number). Then the relative changes in the total pressure difference between the simulation and the measurement were recorded in the last column of the table. The test results illustrated that the simulation model was less sensitive to the changes made to the horizontal separations, especially the roof and corridor floor slabs. Table 22. Sensitivity Analysis Results Variable Name Unit Value from calibrated model Value to change Change Percentage [%] Change in the simulation results [%] Exhaust Vent cm 2 /item % 148.1% Window cm 2 /m % 101.0% Exterior Wall cm 2 /m % 70.3% Floor (Suite) cm 2 /m % 60.2% Interior Wall cm 2 /m % 55.3% Roof cm 2 /m % 36.5% Floor (Corridor) cm 2 /m % 8.5% Shaft wall cm 2 /m % 3.1% 86

100 Appendix B. Evaluation Metrics Appendix B contains research and details about the evaluation metrics that supplement information in Chapter 3. In evaluating the effectiveness of compartmentalization strategies, door operability was one of the criteria to assess the building performance. Exceeding the pressure differential thresholds, as recorded in Section 3.6.2, could lead to difficulties in opening or closing doors. Some of the pressure differential allowances were retrieved directly from the literature, while others were acquired from calculations based on building codes. Details of calculation procedures and assumptions are discussed in the following sections. 8.1 Stairwell Door In accordance with the Ontario Fire Code Door Release Hardware, the maximum force applied to open the fire exit door in the direction of exit travel, when the latch is released, should be less than 90 N ( Ontario Fire Code, 2018). From the literature, it was mentioned that many jurisdictions required the stairwell door to be opened with no more than 90 N (Lovatt & Wilson, 1994). Therefore, the limitation on the pressure difference across the stairwell door could be calculated using the concept of lever arm. One previous study has conducted field measurements on the stairwell doors. It stated that a pressure difference of 65 Pa was calculated across the stairwell doors for floors 2 and 41. This equates to a force of 130 N acting on the door and an opening force about 100 N, or 22 lb, for the door on floor 41 opening into the stairwell (Lovatt & Wilson, 1994). If it was assumed that the opening force did not account for the force required to set the door panel in motion, and the door was opened slowly under equilibrium, a schematic diagram could be drawn to represent forces acting on the door in Figure

101 Figure 15. Diagram of the Inputs to Calculate the Lever Arm of the Opening Force Since a pressure of 65 Pa has resulted in an equivalent force of 130 N, the door panel area would be 2 m 2 (2 m * 1 m) using F = ma. Assuming the equivalent force of the pressure difference would act at the central point of the door panel, the horizontal lever arm for the pressure force was then 0.5 m. Therefore, using the equation of F - d - = F / d /, the horizontal distance from the door hinge to where the opening force applied would be 0.65 m. Applying the same lever principle, the maximum pressure difference across the stairwell door could be calculated as illustrated in Figure 16. When a 90 N force was applied at 0.65 m from the door hinge, the resulted pressure equivalent force was 117 N. Converting from force to pressure, the maximum pressure differential allowed across the stairwell door is 58.5 Pa. 88

102 Figure 16. Diagram of the Inputs to Calculate Maximum Pressure Difference When Opening the Stairwell Door The opening direction of the stairwell door is required to align with the exit travel direction, which means the door should be opened from the hallway to the stairs. In winter, stairwell door opening issues might occur on the upper floors where the stairwell pressure is greater than the corridor pressure due to stack effect. On the other hand, the pressure differential direction on the lower floors is usually from the corridor to the shaft, which would actually help open the stairwell doors. Meanwhile, a tremendous corridor pressure might result in difficulties of properly closing the door. For the lack of information about the requirements of closing stairwell doors, the numerical limitation of the pressure difference from the hallway to the shaft could not be provided in this research, and therefore, it is not included in the evaluation metrics. 89

103 8.2 Suite Entrance Door Similarly, the serviceability of suite entrance door is governed by the pressure differentials as well. It was assumed that the suite entrance door was installed to open into the suites. Therefore, the pressure differential allowance could be determined by the maximum force applied by the tenant to open the suite door and the maximum force provided by the door closer to retract the door to fully closed position. When opening the suite entrance door, the ADA Standards for Accessible Design 2010 has set the requirements of the force for opening a door or gate other than fire doors in Section The act stipulates that the force for opening interior hinged doors should be less than 5 pounds (22.2 N), which pertains to the continuous application of force necessary to fully open a door, not the initial force needed to overcome the inertia of the door (Department of Justice, 2010). Nation Building Code has a similar requirement on the opening force as 22 N for the interior door, but the doors at the entrance of a dwelling unit are not included in the clause (National Building Code, 2010). The suite entrance door size was assumed to be 3 by 6 8 (0.914 m by m), which is one the common door size used in North America, and the door handle was located 7 mm away from the door edge. Using the equation of F - d - = F / d /, the pressure difference across the suite entrance door should be no greater than 24 Pa, as shown in Figure

104 Figure 17. Diagram of the Inputs to Calculate Maximum Pressure Difference When Opening the Suite Entrance Door On the other hand, the maximum pressure differential is also determined by the door closing device. Door closers are required in some jurisdictions, such as Toronto, to be installed at the suite entrance door to automatically shut the door after the occupant leaves and prevent the spread of smoke and fire into the corridor (City of Toronto, n.d.). The minimum closing force that a door closer can provide is tested and categorized in accordance with the ANSI/BHMA Standard A156.4: Door Controls (BHMA, 2000). The conversion between the door closer grade and the closing force is shown in Table

105 Table 23. Minimum Closing Force Provided by Door Closers Door Closer Size Minimum Closing Force [lb] Minimum Closing Force [N] Most commercial products of door closers have the ability to adjust closing force to grade 6. Therefore, 62.3 N was selected to be the closing force so that any pressure differential across the suite entrance door exceeding this value would cause operation issues. The lever arm of the door closer various slightly among different products. For instance, The horizontal distance from the hinge to the door closer is mm for a regular arm door closer (CRP Securities, n.d.), and mm for another similar door closer (Yale, n.d.). Since the difference of the installation location was relatively minor, it was assumed that the lever arm for the closing force provided by the door closer was 280 mm. Illustrated in the Figure 18, the maximum pressure difference across the suite entrance door was 20.5 Pa, slightly lower than the requirement for opening doors. 92

106 Figure 18. Diagram of the Inputs to Calculate Maximum Pressure Difference When Closing the Suite Entrance Door 93