Optimizing Indoor Environments for Occupant Satisfaction Presented by: Kelli Goldstone April 2016
Outline Function of HVAC Thermal Comfort Air Distribution Radiant Heating / Cooling Case Study
Function of HVAC
Function of HVAC What is the function of an air distribution system? A major function of an air distribution system is to provide thermal comfort to building occupants.
Thermal Comfort Definition Statistics Factors Methods
Thermal Comfort Definition ASHRAE Standard 55 condition of the mind which expresses satisfaction with the thermal environment Occupant defines thermally comfortable Physiological & Psychological States Mood Experiences
Thermal Comfort Definition Can we make 100% of a building occupants comfortable? Why, or why not?
Statistics Goal 80% Occupant Satisfaction Thermal Comfort is easy to define, hard to obtain 11% Air Quality and Thermal Comfort in Office Buildings: Results of a Large Indoor Environmental Quality Survey Proceedings of Healthy Buildings 2006, Hiuzenga, et al., Lisbon, Vol. III, 393-397
Statistics Goal 80% Occupant Satisfaction Indoor Air Quality 26% Air Quality and Thermal Comfort in Office Buildings: Results of a Large Indoor Environmental Quality Survey Proceedings of Healthy Buildings 2006, Hiuzenga, et al.,lisbon, Vol. III, 393-397
Thermal Comfort Factors Goal is 80% Acceptance How do we obtain thermal comfort? For given values of humidity, air speed, metabolic rate, and clothing insulation, a comfort zone can be determined. We define the comfort zone in terms of a range of operative temperatures (combination of air temperature and mean radiant temperature) that will provide an acceptable thermal environment.
Thermal Comfort Factors Occupant Characteristics Metabolic Rate Clothing Air Temp Radiant Temp Air Speed Humidity Thermal Environment Conditions
Thermal Comfort Factors Heat Balance Heat gain or loss can occur through: Conduction transfer from body to air Convection transfer by air motion relative to body Radiation transfer by direct exchange Evaporation sweat Warm Just Right? Cold
Thermal Comfort Factors Metabolic Rate(s) May vary by occupant based on occupant activities Restaurant: Diner (1 met) & Server (2 met) Use data in Table 5.2.1.2 for most comparable activity Activity (subset 5.2.1.2) Met W/m 2 Btu/h ft 2 Seated, writing 1.0 60 18 Standing, filing 1.4 80 26 Walking on level surface, 2 mph 2.0 115 37 Machine work 1.8-4.0 115-140 37-44 Calisthenics, exercise 3.0-4.0 175-235 55-74 Dancing, social 2.4-4.4 140-255 44-81 1 Met 108W 353 Btu/h based on Average Adult surface area 1.8 m 2 (19.6ft 2 )
Thermal Comfort Factors Clothing (Insulation) Tables 5.2.2.2A & 5.2.2.2B clo Clothing Description (Typical Ensembles) 0.57 Trousers, short-sleeve shirt 1.01 Trousers, Long-sleeve sweater, T-shirt 0.54 Knee-length skirt, short-sleeve shirt (sandals) 1.04 Knee-length skirt, long-sleeve shirt, half slip, suit jacket clo: Unit of thermal insulation 1 clo= 0.155 m 2 C /W = 0.88 ft 2 h F/Btu
Thermal Comfort Factors Factors for Graphical and Analytic Methods Operative temperature, : based on average air temperature, t a and mean radiant temperature, Case 1: can be used in place of when: 1. No radiant, and/or radiant heating/cooling system 2. Window Solar Heat Gain Coefficient (SHGC) < 0.48 Case 2: t a t r A is based on relative air velocity, t o to Ata 1 A tr v 40 fpm; A 0.5 t o r 40 v 120 fpm; A 0.6 r 120 v 200 fpm; A 0.7 r
Thermal Comfort Factors Factors for Graphical and Analytic Methods Operative temperature, : based on average air temperature, t and mean radiant temperature, Case 3: Occupants with 1.0<met<1.3 No direct sunlight Average air speed < 40fpm t r t a a 7 F t o t r t o t a 2 t r
Graphical Method Graphical Methods Metabolic (MET) rates between 1.0 and 1.3 Clothing Insulation (CLO) between 0.5 1.0 Air speed < 40fpm
Analytical Method Analytical Method Metabolic rates between 1.0 and 2.0 Compliance is defined as: -0.5 < PMV < +0.5 PMV -> Predicted Mean Vote Average occupant thermal sensation Uses assumptions at to clothing and activity levels Related to PPD (Percent People Dissatisfied)
Analytical Method Analytical Method PPD is an empirical profit fit of Thermal SENsation Surveys (TSENS) A PMV of ±0.5 is equivalent to PPD of 10% (Based on TSENS Data) Due to localized discomfort, an additional 10% PPD is expected PMV of ±0.5 is equivalent to PPD of 20% (local discomfort impact)
Thermal Comfort Factors Analytical Method Analytic Method ASHRAE Thermal Comfort Tool www.ashrae.org CBE Thermal Comfort Tool www.cbe.berkeley.edu
Thermal Comfort Factors Analytical Method Comfort Zone Methods How to select diffusers to achieve <40fpm Use displacement system Use underfloor system Use diffuser mapping to select overhead diffusers
Thermal Comfort Factors Designing for Velocities >40fpm Standard Effective Temperature (SET) Temperature of an imaginary environment at: 50%rh, ta <20 fpm, tr ta Total heat loss from skin of imaginary occupant with 1.0 met and 0.6 clo is the same as that from a person in the actual environment, with actual clothing and activity level SET is used to evaluate all cases of comfort with local air velocity above 40 fpm
Thermal Comfort Factors Designing for velocities >40fpm Standard Effective Temperature (SET) Figure 5.3.3.B
Thermal Comfort Factors Acceptable ranges of operative temperatures and average air speed for the 1.0 and 0.5 clo comfort zone, humidity ratio 0.010
Thermal Comfort Factors Local Discomfort Shoot for 80% Acceptance < 20 PPD (Predicted Percentage Dissatisfied) Dissatisfaction due to Draft Dissatisfaction due to Other Sources Draft Draft Vertical Air Temperature Difference Warm or Cool Floors Radiant Asymmetry <20% <5% <10% <5% At t o below 22.5C (72.5F), t a shall not exceed 0.15 m/s(30 fpm)
Thermal Comfort Factors Local Discomfort Radiant temperature asymmetry Ceiling Warmer than Floor Radiant Temperature Asymmetry C ( F) Ceiling Cooler than Floor Wall Warmer than Air Wall Cooler than Air <5 (9.0) <14 (25.2) <23 (41.4) <10 (18.0)
Thermal Comfort Factors Local Discomfort Vertical Air Temperature Difference 3 C (5.4 F) Included in DV Calculations
Thermal Comfort Factors Local Discomfort Floor Surface Temperature When occupants are seated with feet in contact with floor 19 C (66.2 F) floor surface 29 C (84.2 F)
Thermal Comfort Factors Local Discomfort Cyclic Variations, t o 1.1 C (2 F) for period of cycle <15 minutes Drifts and Ramps, t o Time Period 0.25 h 0.5 h 1 h 2 h 4 h Max Operative Temperature Change 1.1 C (2.0 F) 1.7 C (3.0 F) 2.2 C (4.0 F) 2.8 C (5.0 F) 3.3 C (6.0 F)
Naturally Ventilated Spaces (Adaptive Model) There is no mechanical cooling system (e.g., refrigerated air conditioning, radiant cooling, or desiccant cooling) installed. No heating system is in operation. Representative occupants have metabolic rates ranging from 1.0 to 1.3 met. Representative occupants are free to adapt their clothing to the indoor and/or outdoor thermal conditions within a range at least as wide as 0.5 to 1.0 clo. The prevailing mean outdoor temperature is greater than 10 C (50 F) and less than 33.5 C (92.3 F).
Naturally Ventilated Spaces (Adaptive Model)
Case Study PROJECT #1: Overhead VAV Minimum Flow Reduction
Frequency Project #1: VAV Minimum Reduction Retro-commissioning & ASHRAE Research Reduce energy use of VAV systems Energy code adoption of low minimum VAV control Title 24-2008 ASHRAE 90.1-2013 Existing buildings retrofit opportunity with less than 1 year payback Barriers to market acceptance VAV controller stability Resolved (PG&E, ASHRAE RP 1353) Potential occupant comfort issues? Dumping diffusers Poor room air mixing MIN zone for 1 year MAX Cooling airflow
VAV Minimum Reduction Objective and Method Objectives Measure energy savings & validate simulations Identify comfort issues that may occur at low flow Funding California Energy Commission - PIER ASHRAE UC Berkeley - Center for the Built Environment Method Field Study in 7 buildings Background survey Right now survey matched to zone trends Energy monitoring Laboratory Study Air distribution for various diffuser types
Yahoo! Sunnyvale Campus B A E D C F G Energy Meter A,B,E,G
Intervention schedule, over 1.5 years
Measured flow fractions: Yahoo campus Warm Season All Occupied Hours Cool Season All Occupied Hours Density 0.00 0.05 0.10 0.15 Low Minimum 30% Minimum Density 0.00 0.05 0.10 0.15 Low Minimum 30% Minimum 0 20 40 60 80 100 0 20 40 60 80 100 Flow Fraction [%] Flow Fraction [%]
% dissatisfied of people "How satisfied are you with the temperature in your workspace? HIGH min flow rate 30.0% 249 25.0% 20.0% 681 15.0% 10.0% 463 1408 1793 766 5.0% 0.0% 800 Ferry 800 Ferry Building Building Warm season Yahoo! Cool season Yahoo! Warm season % Dissatisfied people HIGH LOW 800 Ferry Building warm season 27.3% 12.5% Yahoo! cool season 8.7% 9.4% Yahoo! warm season 20.1% 10.3%
Thermal Sensations Yahoo warm season, 1865 votes HIGH min flow rate LOW min flow rate 60% 37.4% 55.9% 50% 40% 24.2% 41.6% 30% 20% 21.5% 16.1% 16.7% 16.8% 10% 0% 5.5% 3.3% 10.4% 4.8% Cold (-3) Cool (-2) Slightly cool (- 1) Neutral (0) Slightly warm (1) 4.3% 2.9% 0.1% 0.2% Warm (2) Hot (3)
Air temperature under high & low min flows (800 Ferry building) High flow: average Tair = 71.2ºF Low flow: average Tair = 73.3ºF 800 Ferry Building - Zone Temperature 85 HIGH minimum flow rate LOW minimum flow rate 80 75 70 65 60 09/22 09/23 09/26 09/27 09/28 09/29 09/30 10/03 10/04 10/05 10/06 10/07 10/10 10/11 10/12 10/13 10/14 10/17 10/18 zone temperature [F] 10/19 10/20 N Mean sd 14 27 23 35 45 36 35 41 47 34 65 23 30 51 45 64 25 37 67 27 48 72 72 71 71 72 71 71 71 70 71 71 72 73 74 74 73 74 74 75 75 73 1.4 2 1.8 1.5 1.6 1.5 1.4 1.8 1.6 1.5 2 0.89 1.6 1.5 1.1 1.9 1.1 1.4 1.3 1.2 2.1 Dates
Loads are surprisingly low California T24 minimum ventilation.15.23.5 1 CFM/FT 2 at 20 F ΔT 140 Zones, 2 buildings, 1 warm month (Sept)
What happens when the loads are lower than the VAV minimum? Cooling setpoint Space temperature Heating setpoint Zones spend a lot of time at heating setpoint in cooling season. Explanation for summer cold complaints. See ASHRAE 2012 Chicago Seminar 14, Why Are We Over Cooling Buildings in the Summer
800 Ferry average temperature vs. Standard 55 800 Ferry Building Sept. 2011 Heating Setpoint 69-75 F Cooling Setpoint 30-50% VAV mins Existing 10-15% VAV mins ASHRAE -55 SUMMER COMFORT ZONE
Sense of air movement Have you noticed any air movement in your workspace? No air movement A moderate amount A little Strong air movement Moderate and strong votes (% of total votes) VAV flow rate < 30% 30% - 40% >90% Yahoo! warm season 11 11 20 Yahoo! cool season 7 4 13 800 Ferry building 9 16
Measured energy Savings 8%-20% energy cost savings ~ 1 year payback (retrofit) Immediate payback for new construction
Air Distribution Laboratory Testing Price Labs 8x6 520 Grille Smoke Pattern Testing Chamber
Temperature & Air Speed distribution Representative results Price PDN perforated face diffuser Temperature is more even at lower flow Air speeds decrease at lower flow Air speeds below 30 fpm draft limit Similar results for all other ceiling mounted diffusers
Comfort Metrics Draft, vertical stratification, ADPI ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy Air Speed average air speed at three heights over 1-3 minutes Draft limit below 72.5 F the air speed limit is 30 ft/min Air speed limit above 72.5 F & no occupant control, 160 ft/min Vertical temperature limit 5.4 F from head to ankle ADPI Air Diffusion Performance Index. Measure of mixing. Well mixed ADPI > 80% ensures ASHRAE 55 vertical air temperature limit per ASHRAE Fundamentals Ch. 20
Air Diffusion Results Summary Diffusers Flush with Ceiling (PDF, PDN, SDB, SPD) 98-100% ADPI regardless of flow or temperature Lower air speeds at lower flow Average air speed below ASHRAE 55 draft limit Lower air speed at 65 F discharge temp compared to 55 F No Ceiling (RCD, 520 grille) 87-100% ADPI at 65 F Lower air speeds at low flow Average air speed below ASHRAE 55 still air limit Sidewalls can dump at 55 F and low flow
VAV minimum reduction conclusions Counter to the original hypothesis, comfort improves rather than gets worse Explanation for summer over-cooling Dumping & draft do not occur at low flow Ventilation is maintained Energy savings is significant and similar to simulation predictions Significant retrofit opportunity for existing building with DDC controls. Less than 1 year payback. More detail : 1) ASHRAE Dallas 2013, Seminar 70 Save Energy and Improve Occupant Comfort with Advanced VAV Zone Controls 2) Science and Technology for the Built Environment, 2015, Effects of Diffuser Airflow Minima on Occupant Comfort, Air Mixing, and Building Energy Use (RP-1515)
Conclusion ASHRAE Standard 55-2013 is code intended Thermal Comfort is subjective Thermal Comfort Factors need to be part of your design Overhead mixing does not equal draft generation
Questions