Practical research on effective use of simulation for HVAC systems in the retro-commissioning process H. Tanaka 1, S. Ito 2, Y. Morikawa 3, Y. Akashi

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1 Practical research on effective use of simulation for HVAC systems in the retro-commissioning process H. Tanaka, S. Ito, Y. Morikawa, Y. Akashi, and M. Yamaha Campus Planning&Environment Management Office, Nagoya University, Nagoya, 6-86, Japan SANKI Engineering Co., Ltd., Akashicho, Chuo-ku, Tokyo, -86, Japan Kiuchi Construction Co., Ltd., kuniyoshida, Suruga-ku, Shizuoka, -86, Japan Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, -866, Japan College of Engineering, Chubu University, Kasugai, Aichi, 87-86, Japan ABSTRACT This paper discusses a method and significance of utilizing simulations for HVAC systems in a retro-commissioning process. In the retro-commissioning project in this study, the performance of air-side HVAC systems were verified based on operational data derived from BEMS (Building Energy Management System) and short-term simple measurements. Also, system simulations were conducted for the air-side HVAC system with operational data to evaluate the effect of future retrofit. The LCEM tool was used to examine and simulate the effect of reducing the electricity consumed by fans by replacing air distribution system from CAV to VAV. The results indicate that VAV retrofitting may cut energy consumption by % in summer season, by 6% in winter on the entire typical office floor. The behavior of air-side HVAC system, and energy performance after retrofit improvement could be estimated by using system simulation based on actual operational data. KEYWORDS Retro-commissioning, System simulation, LCEM tool, Operational data, BEMS INTRODUCTION In the retro-commissioning process, if the actual operational data for HVAC system is obtained and saved by BEMS and the like, to suggest options for the system improvement on the ground of this operational data is very important task for the commissioning team. In addition, system simulation by using the operational data provides more reliable results for the suggestions. The application of this approach, there are some practical examples for the HVAC heat source system, but the application example for air-side HVAC system is extremely small. Therefore, the purpose of this study is to show a specific application example.

2 Table. Specifications of AHU Air volume and Input in ( ) after adjustment by fan Inverter. AC- No. Specifications Office on north side Capacity: Cooling.kW, Heating.6kW Air volume:7,7m /h, Fresh air:, m /h Capacity: Cooling.kW, Heating 9.kW Air volume:7,m /h (,8 m /h) Fresh air:,9 m /h Capacity: Cooling 8.6kW, Heating.kW Air volume:7,m /h (6, m /h) Capacity: Cooling.kW, Heating 9.kW Air volume:7,m /h (,6 m /h) Fresh air:,9 m /h Capacity: Cooling 9.kW, Heating.6kW Air volume:7,m /h, Fresh air:, m /h Input kw [VAV].7.7 (.).7 (.9).7 (.) [VAV].7 AC- No Specifications Office on south side Capacity: Cooling 7.7kW, Heating.6kW Air volume:7,7m /h, Fresh air:, m /h Capacity: Cooling.kW, Heating.kW Air volume:7,m /h (,7 m /h) Fresh air:,9 m /h Capacity: Cooling.6kW, Heating 6.kW Air volume:,m /h (,76 m /h) Capacity: Cooling.kW, Heating 9.kW Air volume:7,m /h (,8 m /h) Fresh air:,9 m /h Capacity: Cooling.kW, Heating.6kW Air volume:7,m /h, Fresh air:, m /h Input kw [VAV].7.7 (.). (.8).7 (.) [VAV].7 OUTLINE OF THE SYSTEM The facility that a retro- AC- commissioning process is applied is AC- AC- AC- AC- an office building (completed in 99) with seven floors above ground and about, m total floor area. Supply heat for cooling/ heating is distributed to this building from an energy plant within the premises. The building is air-conditioned by single duct AHU AC- AC- AC- AC- (air handling unit) systems with AC- VAV (variable air volume) and CAV Figure. Typical floor plan of the building (constant air volume) control. Figure and Table show the AHU zoning on the typical floor (the rd floor), and the specifications of the air conditioners. The typical floor has office zones on the north and south sides. Their interior zones are air-conditioned by two AHUs with CAV control. The perimeter zone on the north and south sides are air-conditioned with CAV air handlers without fresh air. The perimeter zone on the east and west sides are air-conditioned with VAV air handlers. In terms of introducing outdoor (fresh) air, respective AHU acquire a constant air volume by means of CAV units. COMPREHENSION OF THE HVAC SYSTEM OPERATION () Overview of simple measurements and evaluation method During the air-conditioning period (Jul. Sep.9, and (Nov. Dec7, ), temperature and humidity data for the indoor air and air conditioner outlet/inlet air was obtained by short-term simple measurements and BEMS (Building Energy Management System) to identify the behavior of the air conditioners. The fan currents of AHUs on the VAV control were measured in time series.

3 Table. Simple measurement point :BEMS data, :short-term simple measurement AC No. Room air Temp. Supply air Temp Supply air RH Return air Temp. Return air RH,, 6, Assumed 9% Room Temp.,, 7, 9, 8 VSA hsa Supply air AHU Fan Coil hra hma VOA CAV unit hoa Fresh Air VRA Return air V h RA MA V SA V V RA VSA qc.8 h OA RA V VSA OA h OA hma hsa / 6 Figure. Overview of calculating a heat extraction rate of AHU The measured currents and manufactural specifications of the characteristics curve current vs. supply air volume were used to estimate the supply air volume and fan electric power consumption of AHU and to calculate the heat extraction rate of AHU, etc. The supply air volume of AHU on the CAV control was estimated based on the current and voltage values (after inverter control), which were checked by spot measurements. Table shows simple measurement points for temperature and humidity. () Evaluation of the behavior of the air-side HVAC system Figure shows an overview of calculating the heat extraction rate of AHU using simple measurement data. V, h, qc are air volume[m /h], specific enthalpy[kj/kg] and heat extraction rate of AHU coil [kw], and subscripts SA, MA, RA and OA are supply air, mixed air, return air and outdoor (fresh) air, respectively, in the figure. Figure shows examples of analysis results of the heat extraction rate of AHU in cooling/heating season. The amount of heat removed by AC- and 8 is very small throughout the period, partly due to mutual interference with adjacent AHUs. AC- and 8 were mainly used for air circulation even in the main air-conditioning period. One of the options is to stop these AHUs because outside air is not introduced. The CAV system is subject to large load fluctuations, and is mostly operated in the heat load range much lower than the rated capacity. This indicates that energy consumption may be significantly reduced by retrofitting to VAV system. SYSTEM RETOROFITTING SIMULATION () Outline of the simulation modeling LCEM tool Ver.. (MILT ) was used to simulate the effect of reducing the electricity consumed by fans by retrofitting AHUs (AC-,,, 7, 8, and 9) from CAV to VAV. Figure shows an example object of system elements supplied by LCEM tool and its data flow (Ito 7 et al.). The object is composed of Communication, Control, Method(calculation) and Property(specification) sections.

4 Heat extraction rate of AHU coil [kw] Cooling Capacity [kw] Supply air volume [m/h] Return air volume [m/h] AC- VAV AC- CAV 7 9/ 8/ 8/ 8/ 8/ 8/ 8/ 7/ 7/ 7/ 7/ 9/ 8/ 8/ 8/ 8/ 8/ 8/ 7/ 7/ 7/ 7/ AC- CAV AC-8 CAV 7 Air Volume ( /h) 9/ 8/ 8/ 8/ 8/ 8/ 8/ 7/ 7/ 7/ 9/ 8/ 8/ 8/ 8/ 8/ 8/ 7/ 7/ 7/ 7/ 7/ Heat extraction rate of AHU kw) Air Volume ( /h) Heat extraction rate of AHU kw Figure -(a). Heat extraction rate of AHU in cooling season Heat extraction rate of AHU coil [kw] Heating Capacity [kw] Supply air volume [m/h] Return air volume [m/h] 7 AC- CAV AC- VAV /6 / /6 / /6 / /6 / /6 / / /6 / /6 / /6 / /6 / /6 / /6 / /6 AC-8 CAV 7 /6 / /6 / /6 / /6 / /6 / /6 / /6 / /6 /6 / /6 / /6 / /6 / / AC- CAV Air Volume ( /h) Heat extraction rate of AHU kw Air Volume ( /h) Heat extraction rate of AHU kw Figure -(b). Heat extraction rate of AHU in heating season Each object exchanges information with only the neighboring objects on both sides. In this process, the objects calculate the output(s) based on an energy balance calculation. The calculation adopts a static simulation and its time step is one hour. Regarding the AHU fans, each P-Q characteristic curve (air volume vs static pressure) and motor efficiency are refracted to the fan object. And pressure and power consumption of fan are calculated under supply air volume (B) as shown in Figure.

5 () Assumption and boundary condition In this simulation, it is supposed that each AHU meets the same thermal load after retrofitting from CAV to VAV control. In the LCEM tool, objects were connected as shown in Figure 6 to develop a modeling of the AHU systems. The cooling/heating water coil objects used in the simulation were selected from LCEM tool that are close to actual coil specifications. The air conditioner fan specifications were checked for the P-Q characteristics of AHU fans, and were used for the fan modeling. The minimum supply air volume of AHU was set to each outdoor (fresh) air volume. The boundary conditions are as follows: cooling/heating water coil inlet water temperature: 7 C/ C, air supply temperature: 6 C/ C (based on the actual situation), outdoor air temperature and relative Outside Air Cooling Tower Cooling pump WB Temp. [ ] 6. ON/OFF()ON=, OFF=) ON/OFF()ON=, OFF=) Water Flow Rate [l/min], Water Flow Rate [l/min], Outlet Water Temp. [ ] 8. Supply Cooling W Temp. [ ] 8. Inlet Water Temp. [ ] 7. Return Cooling W Temp. [ ] 7. WB Temp [ ] 6. CONTROL Cooling Water SP [ ] 8. Ratio of Water Flow [%] TD Sim [ ] 6. Fan Powe [kw].8 Outlet Water Temp. [ ] 8. ERROR good SPECIFICATION Fan Power DP(kW). Water Flow Rate DP [l/min], Adjustment Paramete a. Adjustment Paramete b. Figure. Example of Object (Cooling Tower) Air Volume [ m /h] B: Required Volume A C :CAV A D :VAV (P=const.) A E :VAV (P Q.) Figure. The model of fan control humidity: actual measurement values, room heat load: calculation values based on actual measurements, room reference temperature and humidity: actual room temperature and humidity derived from central monitoring. The room sensible/latent heat load and room reference temperature and humidity are given as boundary conditions based on actual measurements (room temperature and humidity, supply air temperature and humidity, and supply air volume). The outdoor air heat load is added to the coil load calculated by the introduced outdoor air volume and its air temperature and humidity by time of day. INPUT: outdoor air INPUT: supply water temp. boundary fresh air volume outdoor air condition supply water boundary cooling/ heating coil AHU unit (humidifier) AHU unit (fresh air) fan (supply, return) OUTPUT: OUTPUT: OUTPUT: return water temp. heat extraction rate fan power supply water volume air state static pressure duct VAV CAV unit INPUT: room heat load ref. temp.& RH AC on-off room boundary Figure 6. AHU system diagram of LCEM tool

6 RESULTS AND DISCUSSION Figure 7 shows the results of retrofitting CAV systems to VAV systems for the typical office floor, and Figure 8 shows the details of system behavior. Table shows ATF (Air Transport Factor: indoor sensible heat load/electric power consumption by fans) calculation results before and after retrofitting, based on actual measurements and simulation results. The results indicate that VAV retrofitting may cut energy consumption by % in cooling season, by 6% in heating season on the entire typical office floor. ATF was improved more than double from 8 (at present) to 6 in summer, from (at present) to 8 in winter. In particular, a large effect was obtained in winter. Also note that it is assumed that the operation of AC- and 8 are stopped in winter, because heat extraction rate of these AHUs have been almost zero during heating season in actual operation. Therefore, their ATFs have been hidden in Table. In addition, energy efficiency can be improved by stopping the AC and 8, but there is the potential for a negative effect on the indoor air quality and the temperature distribution. CONCLUSION AND IMPLICATIONS The behavior and the performance of the air-side HVAC system could be verified using operation data derived from BEMS and short-term easy measurements. Table. ATF(Air Transport Factor) of AHU Cooling season: Heating season: AC No. 6 Actual Retrofit AC No entire floor Actual Retrofit AC No. 6 Actual Retrofit AC No entire floor Actual Retrofit AC,,6 and are VAV system already, their ATF is the same value before and after retrofitting Fan Power consumption (MWh) AC AC. AC9 AC8 AC7 AC6 AC AC AC AC CAV 合計 Jul. ~ Sep. Reduction rate 9%. VAV 合計 Fan Power consumption (MWh) AC AC AC. AC9 AC8 AC7 AC6 AC AC AC Nov. ~ Dec. Reduction rate 6% Actual condition Retrofit simulation Actual condition Retrofit simulation 8.9 Figure 7. Seasonal electric power consumption of AHU fans

7 Room heat load(kw), RH(%) 8 6 7/ 7/ sensible heat 7/ 7/ 8/ latent heat 8/ 8/ 8/ 8/ 8/ 9/ 7/ 7/ Return Air R.H. 7/ 7/ 8/ Return Air Temp. 8/ 8/ 8/ 8/ 8/ 9/ D.B. Air temp.( ).... 7/ CAV VAV 7/ 7/ 7/ 8/ 8/ 8/ 8/ 8/ 8/ 9/ 7/ 7/ 7/ 7/ 8/ rated value 8/ 8/ 8/ 8/ 8/ 9/.... AC- AC- Room heat load(kw), RH(%) 8 6 7/ 7/ latent heat 7/ 7/ 8/ sensible heat 8/ 8/ 8/ 8/ 8/ 9/ 7/ 7/ 7/ Return Air R.H. 7/ 8/ 8/ 8/ Return Air Temp. 8/ 8/ 8/ 9/ D.B. Air temp.( ).... 7/ 7/ 7/ CAV 7/ 8/ 8/ 8/ VAV 8/ 8/ 8/ 9/ 7/ 7/ 7/ 7/ 8/ 8/ rated value 8/ 8/ 8/ 8/ 9/.... AC- AC-8 Figure 8-(a). Room heat load and hourly power consumption of AHU fans in summer For a VAV system, it can grasp the behavior of system operation such as fluctuation of supply air volume, heat extraction rate of AHU and so on. With a view to employing VAV for air-side HVAC systems to improve operations, it was demonstrated that system simulation by using the actual operational data provides more reliable results for the suggestions of the improvement. ACKNOWLEDGEMENTS The results of this study, it is part of the outcomes of the research committee for an applications of commissioning process (Building Services Commissioning Association, BSCA in JAPAN). I gratefully acknowledge helpful discussion with the committee on several points in this paper. 6

8 Room heat load(kw), RH(%) CAV sensible heat VAV / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 Return Air R.H. Return Air Temp. rated value / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7.... D.B. Air temp.( ) 8 6 Room heat load(kw), RH(%).... AC- sensible heat CAV AC- VAV / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 AC- Return Air R.H. rated value AC-8 Return Air Temp. / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7 /9 / / / /7.... D.B. Air temp.( ) Figure 8-(b). Room heat load and hourly power consumption of AHU fans in winter REFERENCES MILT (Ministry of Land, Infrastructure, Transport and Tourism, Japan),. Life Cycle Management Tool Ver.. ( _lcem.html ) M.Ito, Y.Sugihara et al., Development of HVAC system simulation tool for life cycle energy management, Part : Outline of the developed simulation tool for life cycle energy management, Part : Development of component models for HVAC equipment, Proceedings of Building Simulation 7, pp.6-6, 7 7