Energy modeling of two office buildings with data center for green building design

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1 Available online at Energy and Buildings 40 (2008) Energy modeling of two office buildings with data center for green building design Yiqun Pan *, Rongxin Yin, Zhizhong Huang Institute of Building Performance & Technology, Sino-German College of Applied Sciences, Tongji University, Shanghai , China Received 28 July 2007; received in revised form 22 September 2007; accepted 2 October 2007 Abstract Energy simulation models are developed with EnergyPlus for two office buildings in a R&D center in Shanghai, China to evaluate the energy cost savings of green building design options compared with the baseline building. As a R&D center of an international IT corporation, there are data centers in the two buildings, which make them different from typical office buildings. The data centers house high energy consuming IT equipments and need 24 h air-conditioning every day all year round. In order to achieve energy cost savings, multiple energy efficiency strategies are employed for design proposed building, encompassing high performance building envelope, lighting system, and HVAC system. Through energy modeling, the design proposed options are compared to an ASHRAE compliant budget model to highlight energy cost savings versus standard practice and show the potential LEED TM Credit EA1 Optimize Energy Performance. Meanwhile, they are also compared to China Code model to figure out the energy cost savings versus the most popular practice conforming to China Public Building Energy Saving Design Standard. The whole building energy simulation results show that the yearly energy cost saving of the proposed design will be approximately 27% from China Code building and 21% from ASHRAE budget building, which can achieve 4 points for LEED credit due to energy performance optimization. # 2007 Elsevier B.V. All rights reserved. Keywords: Energy modeling; Green building design; Data center; Energy performance optimization; Whole building energy simulation 1. Introduction Energy modeling is utilized on buildings more often for two main purposes: modeling for building and HVAC system design and associated design optimization (forward modeling), and modeling energy use of existing buildings for establishing baselines and calculating retrofit savings (data-driven modeling) [1]. Forward modeling of building energy use begins with a physical description of the building system or component of interest. For example, building geometry, geographical location, physical characteristics (e.g., wall material and thickness), type of equipment and operating schedules, type of HVAC system, building operating schedules, plant equipment, etc., are specified. The energy use of such a building can then be predicted or simulated by the forward simulation model. Forward modeling can help designers compare various design * Corresponding author. Tel.: ; fax: address: yiqunpan@mail.tongji.edu.cn (Y. Pan). options and lead them to energy-efficient designs in manner of cost-effectiveness. There are many building energy simulation software available nowadays. Some are simplified energy analysis tools that only provide a quick analysis of annual energy use of buildings, but some use more detailed models and run on hourly basis that provide detailed hour-by-hour energy analysis of buildings [4]. LEED TM Credit EA1 Optimize Energy Performance [3] specified three compliance path options to evaluate the achievement of increasing levels of energy performance above the baseline in the prerequisite standard. One option is whole building energy simulation, which is to calculate a percentage improvement in the proposed building performance rating compared to the baseline building performance rating per ASHRAE Standard [2] by a whole building energy simulation using the Building Performance Rating Method in the Standard. The standard has many requirements for the simulation programs. DOE-2 and EnergyPlus are programs that meet the requirements. EnergyPlus is regarded as the new-generation building energy simulation program which will replace DOE-2 the /$ see front matter # 2007 Elsevier B.V. All rights reserved. doi: /j.enbuild

2 1146 Y. Pan et al. / Energy and Buildings 40 (2008) most popular program nowadays around the world [5,6]. The advantage of EnergyPlus over DOE-2 is that EnergyPlus uses integrated simultaneous load/system/plant simulation technique instead of sequential simulation technique, so that it can do accurate prediction of space temperature, which is crucial to energy efficient system engineering because system size, plant size, occupant comfort and occupant health are dependent on space temperature information. EnergyPlus also allows users to evaluate a number of processes that DOE-2 cannot simulate well, including under-floor air distribution system, radiant heating and cooling system, ground-source heat exchanger, power generation system, etc. Concerning the features of EnergyPlus, many researchers around the world used it as the building energy simulation and analysis tool. Griffith et al. [7] used DOE-2.1E to develop and model a new building in the Teterboro Airport for energy efficient predesign and subsequently conducted extensive whole-building annual energy simulations using EnergyPlus. Xu [8] constructed EnergyPlus simulation models to investigate different thermal mass discharging strategies to shift heating and cooling demand. Eskin and Türkmen [9] used EnergyPlus to conduct energy simulation to evaluate the interactions between different conditions, control strategies and heating/cooling loads in office buildings in four major climatic zones in Turkey. Ordenes et al. [10] analyzed the potential of seven BIPV (Buildingintegrated photovoltaic) technologies implemented in a residential prototype in three different cities in Brazil by simulation with EnergyPlus. Pan et al. [11 13] developed energy models with EnergyPlus for two BCHP (building cooling heating and power) systems to calculate loads and energy consumptions. In this paper, EnergyPlus is selected as the program to conduct the simulation for the purpose of energy performance optimization of two office buildings in a R&D center in Shanghai, China. 2. Data center buildings The two office buildings are located inside a R&D Center of a famous international IT company. The offices are 5 storeys high above grade, and the floor-to-floor height from 1F to 4F is 4.1 m, and that of 5F is 3.8 m. The total building height is m. The total floor area of the office buildings is 55,413 m 2. The main function of the buildings is office but housing data centers, which are different from typical office buildings. Data centers are normally installed large number of IT equipment (e.g., servers, data storage, network devices, monitors, etc.) to perform various functions such as storage, management, processing and exchange of digital data and information. Energy consumption of data centers is significantly higher than that of commercial office space. Lawrence Berkley National Laboratory (LBNL) conducted studies on 14 data centers in USA and investigated that power demand densities of data centers are in the range of W/m 2 [14], while the power demands typically drawn by commercial office spaces lie in between 50 and 110 W/m 2. Sun and Le [15] examined the energy use of two data centers in commercial buildings in Singapore and concluded that data centers were high energy consuming areas in commercial office buildings. Greenberg et al. [16] benchmarked 22 data center buildings and determined that data center can be over 40 times as energy intensive as conventional office buildings. The huge energy consumptions of data centers demonstrate the significant potential of energy saving, and make them the desired target of energy conservation measures. Greenberg et al. [16] proposed a set of best-practice technologies for energy efficiency of data center buildings including: optimized central chiller plants, free cooling from air-side or water-side economizers, improved uninterruptible power supplies, high-efficiency computer power supplies, etc. The two office buildings are proposed in design to use multiple energy efficiency strategies to achieve the energy savings. These strategies encompass improvements in: Building envelope wall and roof U-factors, glazing performance, and sunshades. Lighting reduction of lighting power density from ASH- RAE maximum. Daylighting installation of daylighting switching/dimming systems in perimeter area. HVAC improved equipment efficiencies compared to ASHRAE minimum, several system enhancements and design options, e.g., under-floor air distribution system, enthalpy wheel, ice storage, air-side free cooling. 3. Model development The study focuses on the investigation of the design proposed options for the two office buildings. Energy simulation models are developed, respectively, for three cases: China Code building, ASHRAE budget building and Design Proposed building. Table 1 lists the input data of envelope, internal loads and HVAC system of the three models. The loads due to equipment and occupants are the same for the three models China code model China Code building is a reference building conforming to current China code [17] and uses VRV (variable refrigerant volume) system in office and air-source chiller for IT rooms, UPS rooms and labs, where 24 h air-conditioning is needed. These air conditioning systems are most commonly used systems in Shanghai area. Since there is no specific module to simulate VRV system in EnergyPlus until the simulation is conducted, unitary air-to-air heat pump system with DX (direct expansion) coil is used to replace it, due to the similarity of the two systems ASHRAE budget model ASHRAE Budget building is an ASHARE compliant building based on the requirements outlined in Chapter 11 of the Standard [2]. Envelope requirements are

3 Table 1 Envelope, internal loads and HVAC system in three models Components China code ASHRAE budget Design proposed Envelope External wall U = 0.97 W/m 2 K U = W/m 2 K U = W/m 2 K Roof U = 0.61 W/m 2 K U = W/m2K U = W/m 2 K Window SHGC = 0.34, SC = 0.4, U = 2.5 W/m 2 K SHGC = 0.26, SC = 0.3, U = 2.45 W/m 2 K SHGC = 0.29, SC = 0.34, U = 2.3 W/m 2 K Shading No South and west façade Infiltration Y. Pan et al. / Energy and Buildings 40 (2008) ACH in perimeter area, 0ACH in internal area Internal loads Lighting Office, IT, UPS, Lobby 12 W/m 2 10 W/m 2 Lab 15 W/m 2 10 W/m 2 Equipment Office, UPS 15.7 W/m 2 Lab 2509 kw IT 240 kw People Office person Office person HVAC system Air distribution system Office VRV system VAV system (with reheat coil in VAV boxes in perimeter area) 0.2 ACH in perimeter area, 0ACH in internal area Perimeter area: induction system with heating and cooling coils Internal area: VAV box, under floor, enthalpy wheel, variable speed fan LAB, IT, UPS CAV system CRAC (computer room air conditioning) system, under floor air distribution, air-side economizer, enthalpy wheel, variable speed fan Secondary system Constant speed pump Constant speed primary chilled water pump/variable speed secondary chilled water pump, variable speed hot water pump Primary system Air-source chiller Four centrifugal chillers (COP = 5.5), 2 gas boilers (h = 80%), two-speed cooling tower, chilled water and hot water supply temperature reset with outside air temperature Variable speed primary chilled water pump, variable speed hot water pump Two centrifugal chillers (3802 kw, COP = 5.949, variable flow), 2 screw chillers (1252 kw, COP = 5.54, variable flow), partial load ice storage for peak shaving, 1 gas boilers (2100 kw, h = 95%), variable-speed cooling tower, hot water supply temperature reset with outside air temperature based on the ASHRAE minimum performance for a building located in Shanghai (based on CDD and HDD). No external shading devices are included in the budget building model. Space heating and cooling are provided by VAV system and code compliant centrifugal chillers and gas boilers. Domestic hot water system is not included Design proposed model The design proposed building is a combination of highefficiency building envelope (shading on south and west façade), high-efficiency lighting system and daylighting dimming in perimeter area, and high-efficiency HVAC system. Under Floor Air Distribution (UFAD) with neutral pressure Plenum (pull type) is used. Computer Room Air-Conditioning (CRAC) system will be employed in IT rooms, UPS rooms and labs, offering the highest cooling capacities with the lowest footprint, operating costs and noise level designed to meet the needs of the latest high density IT Servers. Considering humid climate, energy recovery wheels will recover the heat/cooling energy from the room return air and the pre-cooling coils will be installed for dehumidification of outdoor fresh air. Variable Primary Flow (VPF) system will be applied and the chillers are selected accordingly. There will be 8 sets ice storage coil located in the chiller room with total capacity of 365 RT.H. The ice storage coils will be charged in the night for 8 h during the

4 1148 Y. Pan et al. / Energy and Buildings 40 (2008) Fig. 1. Energy model 3-D view of design proposed building. low power rate period and be discharged in the daytime during the peak power rate period paralleled with chillers. The ice chiller also can run in the daytime as a normal chiller. Fig. 1 is the 3-D view of the design proposed building model. For air-side economizer, no return air temperature limit is set in the model but there is return air enthalpy limit, meaning whenever the enthalpy of air entering the mixer on the outside air side is greater than the return air enthalpy the outside airflow rate is set to the minimum Weather data International Weather for Energy Calculations (IWEC) of Shanghai is used in the simulation. The IWEC are the results of ASHRAE Research Project 1015 by Numerical Logics and Bodycote Materials Testing Canada for ASHRAE Technical Committee 4.2 Weather Information. The IWEC data files are typical weather files suitable for use with building energy simulation programs for 227 locations outside the USA and Canada [18] Zoning The zoning of the building models is made according to the air distribution system. The perimeter zones are separated into four façade south-facing, east-facing, north-facing and Fig. 2. (a) Occupancy schedule of office. (b) Lighting and plug schedule of office. (c) Air distribution system operating schedule of office. Table 2 Energy rates for commercial building in Shanghai Electric rate (RMB/kWh) Spring, Autumn, Winter Peak time 8:00 11:00, 18:00 21: Normal time 6:00 8:00, 11:00 18:00, 21:00 22: Valley time 22:00 6: Summer (July, August, September) Peak time 8:00 11:00, 18:00 21: Normal time 6:00 8:00, 11:00 18:00, 21:00 22: Valley time 22:00 6: Demand charge 30 RMB/kW*month (according to the maximal demand) Gas rate 3.3 RMB/Nm 3

5 Y. Pan et al. / Energy and Buildings 40 (2008) Table 3 Energy consumption summary of China code, ASHRAE and design proposed Energy consumption and cost Electricity Gas Total cost kwh Cost (RMB) Nm 3 Cost (RMB) China Code 42,253,107 28,540, ,540,332 ASHRAE ,027,668 25,876, , ,543 26,251,978 Design propose 31,482,166 20,573,670 78, ,455 20,833,125 Cost saving vs. China Code 7,707,206 27% vs. Budget 5,418,853 21% west-facing with 4 m distance from the inside surface of the exterior wall. The mechanical rooms and toilets are unconditioned spaces. Labs, IT rooms and UPS rooms are located within internal zones but zoned separately. In each building model, there are 173 zones, among which 133 are conditioned Set points The indoor set point in offices and lobby is 25 8C for cooling and 20 8C for heating with dead band, while single set point of 24 8C is set in labs, IT and UPS rooms. Fig. 3. Monthly electricity consumption of China code, ASHRAE budget and design proposed building. Fig. 4. Monthly gas consumption of ASHRAE budget and design proposed building.

6 1150 Y. Pan et al. / Energy and Buildings 40 (2008) Table 4 Energy consumption summary of ECM options Energy consumption and cost Electricity Gas Total cost Cost savings kwh Cost (RMB) Nm 3 Cost (RMB) vs. budget ASHRAE ,027,668 25,876, , ,543 26,251,978 Option 1 39,111,810 25,924,162 81, ,083 26,192,245 59,733 Option 2 38,535,122 25,500,245 48, ,293 25,660, ,440 Option 3 35,343,065 23,650, , ,558 24,091,088 2,160,890 Option 4 39,181,630 25,675, , ,543 26,051, , Operating schedule Fig. 2 illustrates the schedule of occupancy, lighting and plug and air distribution system in office. Labs, IT rooms and UPS rooms are operating 24 h one day all around a year Energy and source rate The rates of electricity and gas for commercial buildings in Shanghai are listed in Table 2 and are input to the models to calculate the energy cost. The ratio of the electric rate during on-peak period to that during off-peak period is 4.38, which is beneficial for utilizing ice storage system to save energy cost. 4. Simulation results 4.1. Energy cost saving of design proposed building Table 3 and Figs. 3 5 show the simulated results of monthly and yearly energy consumption and costs of design proposed building, compared to China Code building and ASHRAE 90.1 budget building. The results show that the energy performance of the proposed design is much better than China Code, with approximately 27% yearly cost savings. Meanwhile, it is also better than ASHRAE budget building, with approximately 21% cost savings ECM options based on ASHRAE budget building In order to compare the energy saving effects, four ECMs (Energy Conservation Measures) are simulated based on ASHRAE budget model. They are: Fig. 5. Energy cost comparison of China code, ASHRAE 90.1 and design proposed building. Option 1: high-efficiency envelope, with shading. Option 2: daylighting dimming in perimeter area, under the envelope with shading of design proposed building. Fig. 6. Energy cost comparison of ECM options based on ASHRAE 90.1.

7 Y. Pan et al. / Energy and Buildings 40 (2008) the contrary, lighting and HVAC system account for 32 and 16% of the total electricity consumption, respectively. Which shows the green building design can obtain a great amount of energy saving from the system other than the office equipment and IT equipment, i.e., lighting, HVAC system. 5. Conclusions Fig. 7. Electrical consumption breakdown of ASHRAE budget building. Option 3: air-side free cooling in mild seasons. Option 4: ice storage peak-shaving system. Table 4 and Fig. 6 summarize the yearly energy consumption and energy cost savings of the 4 ECM options, respectively, compared to the budget building. Among the options, air-side free cooling has biggest energy saving effect especially for the data centers, and ice storage can shave peak electricity demand and save energy cost of about 200,000 RMB per year. Although high-efficiency envelope does not has so big energy saving effect as the two options above for these types of data center buildings with high internal loads, it can improve indoor thermal comfort and productivity. Daylighting dimming is utilized in perimeter area and set illumination is 400lux, which also shows big energy saving effect compared to ASHRAE budget building Energy breakdown of ASHRAE budget building and design proposed building Figs. 7 and 8 illustrate the breakdown of yearly electricity consumption of ASHRAE budget building and design proposed building. Computers, servers and other office equipment is the biggest electric consumer in both models, which accounts for 68 and 84% of total electricity consumption, respectively. On Energy analysis models are built, respectively, for China Code building, ASHRAE budget building and designed proposed building with whole building energy analysis software EnergyPlus. The China Code building conforms to China Public Building Energy Saving Design Standard and the ASHRAE budget building is compliant to ASHRAE The design proposed building is a combination of highefficiency building envelope, high-efficiency lighting system and daylighting dimming in perimeter area, and high-efficiency HVAC system, which consists of under floor air distribution (UFAD) system, energy recovery wheel, variable primary chilled water system, ice storage system, etc. Models are run with typical weather data of Shanghai to obtain hourly simulation results of energy consumptions. The simulation results are compared to calculate the energy and cost savings of design proposed building based on China Code building and ASHRAE budget building. Moreover, four ECM options are simulated based on the ASHRAE budget building to evaluate their energy saving effects. Energy breakdown is implemented on ASHRAE budget building and design proposed building. Conclusions can be drawn as followed: (1) The energy performance of the proposed design is much better than China Code, with approximately 27% yearly cost savings. Meanwhile, it is also better than ASHRAE budget building, with approximately 21% cost savings, which can achieve 4 points for LEED credit due to energy performance optimization. (2) Among the four ECM options, air-side free cooling has the biggest energy saving effect and ice storage can shave peak electricity demand and save energy cost of about 200,000 RMB per year. Daylighting dimming also shows big energy saving effect compared to budget building. (3) In data center buildings computers, servers and other office equipments are the biggest electric consumer, accounting for 680 and 84% of total electricity consumption, respectively, of ASHRAE budget building and design proposed building. The green building design of the two data center buildings can obtain a great amount of energy saving from lighting system and HVAC system. References Fig. 8. Electrical consumption breakdown of design proposed building. [1] ASHRAE Handbook Fundamentals, Chapter 32 Energy estimating and modeling methods, [2] ASHRAE Standard , Energy Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE Standing Standard Project Committee 90.1, [3] LEED-NC, Green Building Rating System for New Construction & Major Renovations, Version 2.2, U.S. Green Building Council, 2005.

8 1152 Y. Pan et al. / Energy and Buildings 40 (2008) [4] P. Jacobs, State-of-the-Art Review Whole Building, Building Envelope, and HVAC Component and System Simulation and Design Tools, Architectural Energy Corporation, [5] D.B. Crawley, et al., EnergyPlus: creating a new-generation building energy simulation program, Energy and Buildings 33 (4) (2001) [6] U.S. DOE, EnergyPlus Manual, Version 2.0, [7] B. Griffith, S. Pless, B. Talbert, M. Deru, P. Torcellini, Energy Design Analysis and Evaluation of a Proposed Air Rescue and Fire Fighting Administration Building for Teterboro Airport, National Renewable Energy Laboratory, [8] P. Xu, Evaluation of Demand Shifting Strategies with Thermal Mass in Two Large Commercial Buildings, Simbuild 2006, Boston, USA, [9] N. Eskin, H. Türkmen, Analysis of annual heating and cooling energy requirements for office buildings in different climates in Turkey, Energy and Buildings (2007) in press. [10] M. Ordenes, et al., The impact of building-integrated photovoltaics on the energy demand of multi-family dwellings in Brazil, Energy and Buildings 39 (2007) [11] Y. Pan, G. Wu, V. Hartkopf, R. Brahme, Energyplus and its application in a BCHP system simulation, in: The 4th International Symposium on HVAC, Beijing, China, [12] Y. Pan, G. Wu, V. Hartkopf, Whole building energy analysis tool energyplus and its application, Journal of HV&AC (China) 9 (34) (2004). [13] Y. Pan, Z. Huang, B. Zhang, H. Zhou, et al., Feasibility of appling distributing energy supply system in an new hospital in Shanghai, Journal of HV&AC (China) 2 (34) (2004). [14] LBNL, Data center website of Lawrence Berkeley National Laboratory, [15] H.S. Sun, S.E. Lee, Case study of data centers energy performance, Energy and Buildings 38 (2006) [16] S. Greenberg, E. Mills, B. Tschudi, et al., Best Practices for Data Centers, Lessons Learned from Benchmarking 22 Data Centers, ACEEE Summer Study on Energy Efficiency in Buildings, [17] GB , Public Building Energy Saving Design Standard, China National Code, [18] U.S. DOE Energy Efficiency and Renewable Energy, Website for EnergyPlus,