1、Rudai Shan is a PhD student in Building Technology, College of Architecture and Urban Planning, University of Michigan, Ann Arbor, Michigan. Carol Menassa is an assistant professor in Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan. Tiemao Shi is a prof
2、essor in College of Architecture and Urban Planning, Shenyang Jian Zhu University, Shenyang, Liaoning, China. Design Strategies for a Net Zero Energy Building in Severe Cold Climate: A Case Study for China Rudai Shan Carol Menassa, PhD Tiemao Shi, PhD ABSTRACT The currently developing concept of Net
3、 Zero Energy Building should be adaptive for different climate situations. Buildings in the severe cold areas of China have higher energy consumption and gas emission due to large heating energy consumption in wintertime. It is challenging to design and operate a net zero energy building in severe c
4、old climate. This paper will discuss the feasibility of a net zero energy office building design targeting for energy efficiency and environmental sustainability. An on-campus office building is explored as an experimental case study in Shenyang, Liaoning Province in China. The case study, which is
5、called “Sino-Germany Zero-Energy Center”, is one of the first examples of a nearly net zero energy building in the severe cold climate of China. Building simulation is performed to validate the interior lighting environment and annual energy consumption. Energy balance was calculated for the case st
6、udy, with the aim of reaching an electricity target of net zero energy. Precise energy monitoring is implemented during operation. This case study shows that to achieve the goal of energy efficient and environment sustainability, appropriate energy efficient strategies adapted to severe cold climate
7、 should be considered to improve the integrated performance of the building,. INTRODUCTION Building energy in China keeps on growing for the past twenty years (Cai et al. 2009). In 2004, the building energy sector constituted 20.7% of the total national energy consumption in China (Jiang and Yang 20
8、06). China has also overtaken the United States and became the largest energy consumer in the world in 2009 (IEA 2010). Buildings are responsible for most of the energy related greenhouse gas emissions. For example, in the United States, CO2 emission from building sections is about 40% of the total
9、CO2 emissions (U.S. Department of Energy 2011). It also could be found that building energy performance is largely influenced by climate. There have been growing interests in net zero energy buildings (NZEB) which are adapted to local climates in recent years. The definition of NZEB is introduced as
10、 by Marszal et al. and Sartori et al., which focuses on the balance concept, the metric, the period and type of energy included in the energy balance together with the renewable energy supply options (Marszal et al. 2011; Sartori et al. 2012). A number of case studies (Cellura et al. 2011; Brown and
11、 Vergragt 2008; Noguchi et al. 2008; Hernandez and Kenny 2010) and research interest (Torcellini et al. 2006; Marszal et al. 2012; Attia et al. 2013; Hamdy et al. 2013; Li et al. 2013) about NZEBs can be found in existing literatures. Recently, there are more and more NZEB attempts in China, includi
12、ng the “Green Energy Building” inside the campus of Shanghai Jiao Tong university in Shanghai (Deng et al. 2009), the “All Green House” in Shanxi (Jin et al. 2014), and the “Nearly Net Zero Energy Building” by China Academy of Building Research (CABR) in 2014. In these attempts, the successful appli
13、cation in practice depends on the selection of appropriate technical strategies that are adapted to the local climate. In this study, the Sino-Germany Zero Energy Building located on campus of Shenyang Jian Zhu University was conducted, which is intended to identify strategies for an improved proces
14、s and limitations of current strategies, and to be used as a reference for NZEBs in severe cold climate in China. OVERVIEW AND BACKGROUND The Sino-Germany Zero Energy Building (SGZEB) is an office building located on campus of Shengyang Jian Zhu University, in Shenyang, Liaoning, China. The latitude
15、 and longitude of the site are respectively 41.8N, 123.4E, and the average elevation of the urban area is 148 ft (45 meters) above the sea level. The site is characterized as a severe cold climate by Thermal design code for civil building (GB50176-93), with the average temperatures below 14 F (-10 C
16、 ) in January and below 77 F (25 C ) in July (Yang et al. 2008). The building has a rectangular floor plan with total floor area of 17229.80 ft2 (1600.71 m2). The building is composed of two floors above ground and one half-below the ground level. An atrium with skylight connects the two floors abov
17、e ground. This building has just achieved the highest level Triple-Star level, of Green building rating standard (GB50378-2006) by Chinas Ministry of Housing and Urban and Rural Development (MOHURD). The initial goal of this building is to develop a demonstration office building and communication ce
18、nter for university students, which has the functions of demonstrating and presenting the sustainable building technology, as well as of working, teaching, and executing experiment. The building also has function of a laboratory where new sustainable technologies are developed. Figure 1 (a) First fl
19、oor plan, and (b) image of the south elevation METHODOLOGY In the early design stage, passive strategies are mainly considered to be applied in this project, which includes high quality building envelope, natural daylight, natural ventilation, etc. Building simulations are also applied for analysis
20、of these strategies. The purpose is to find the most efficient strategy and demonstrate the feasibility of NZEB in this severe cold climate in China. Building envelopes Thermal insulation design of building envelope is most important and first evaluated in this study. The envelope was first construc
21、ted according to the instructions given by the national standard - Design standard for energy efficiency of public buildings (GB 50189-2005), and the Liaoning Province local standard - Design standard for (65%) energy saving of public buildings (DB 21/T1899-2011). These codes define the limits for t
22、he thermal transmittance of the walls and glazing components. Then the entire building envelope is improved to get a lower heat transfer coefficient. Table 1 shows the comparison between the overall heat transfer coefficients (U-value) imposed by Design standard for (65%) energy saving of public bui
23、ldings (DB 21/T1899-2011) and the proposed envelopes. Table 1. U-value comparison between the baseline and the proposed envelopes External structure Baseline Baseline Proposed Proposed Reduction Percentage Btu/(hft2F) W/(m2K) Btu/(hft2F) W/(m2K) Roof 0.08 0.45 0.02 0.11 76% Wall 0.09 0.5 0.02 0.12 7
24、6% Window East 0.56 3.2 0.15 0.85 73% South 0.51 2.9 0.15 0.85 71% West 0.56 3.2 0.15 0.85 73% North 0.56 3.2 0.15 0.85 73% Skylight 0.46 2.6 0.18 1 62% Floor 0.09 0.5 0.05 0.28 45% The external wall of the building was insulated by 0.92 ft (0.28 m) of graphite polystyrene board with a thermal condu
25、ctivity of 0.006 Btu/hftF (0.035 W/mK). Particular attention is paid to the thermal insulation of the thermal bridges. In the Sino-Germany Zero Energy Building, windows guarantee the maximum insulation according to the national code - Design standard for energy efficiency of public buildings (GB5018
26、9-2005), the local code - Design standard for (65%) energy saving of public buildings (DB21/T1899-2011), and subsequent amendments and additions. The infiltration is set with a leakage air change rate of n50 and an air tightness of 0.6 Air Changes per Hour (ACH). The windows are triple-glazed window
27、s filled with argon gas, which are characterized by a transmittance value of 0.19 Btu/hft2F (1.1 W/m2K) with a 0.02 ft (0.006 m) external glass, two 0.052 ft (0.016 m) gap filled with argon and two 0.016 ft (0.005 m) internal glasses. The average global U-value is 0.15 Btu/hft2F (0.85 W/m2K). The So
28、lar Heat Gain Coefficient (SHGC) is 0.41 and the visual transmittance is 0.53. The window frames are made of a triple pane of wood, thermal foam and aluminum. Table 2 shows the comparison for heating and cooling load between national energy code, local energy code and proposed building. The annual h
29、eating and cooling load has been reduced by 34.4% and 35.9% when compared with national and local energy code respectively. Table 2. Heating and cooling load comparison Annual National code National code Local code Local code Proposed Proposed kBtu kWh kBtu kWh kBtu kWh Heating load 668752 196000 65
30、1057 190814 409935 120145 Cooling load 231443 67832 229604 67293 167133 48984 Total 900195 263832 880661 258107 577068 169129 Atrium thermal environment A glass atrium is placed in the central part of the building, to improve daylight environment for the office area around. In summer time, the atriu
31、m with the opening windows on the roof can improve natural ventilation and reduce the mechanical ventilation energy consumption. In winter time, the skylight on the roof will be closed while the shading system is open. Then the atrium can improve the internal thermal environment of the building to r
32、educe the energy consumption for heating. A shading system is placed on the windows of the skylight, which can be controlled manually or automatically due to the solar radiation. The shading system can help to maintain the thermal environment of the atrium and reduce the heating load in summer time.
33、 Summer operation Winter operation Figure 2 Diagram of atrium thermal environment (a) summer operation, and (b) winter operation HVAC control In the SGZEB there are different kinds of sensors, including CO2 sensors, electrical meters; temperature and humidity sensors; electricity energy consumption
34、meters (lighting, socket, transmission and distribution system, weak current system, power plant, etc. All data collected are stored in a database and then used for data mining operations. The aim of the CO2 sensor for the mechanical ventilation system is to guarantee a high quality of the air in th
35、e auditorium while reducing energy consumption as much as possible. This sensor located in the auditorium measures the presence of carbon dioxide and it activates the air circulation which improves the function usually carried out by natural ventilation. When the CO2 level increases due to the prese
36、nce of people in the auditorium, the fresh air flow is increased through managing the variable air volume devices in the air duct. The ATU is provided with a heat recovery system which has an efficiency of 80%. Mechanical ventilation system stops if windows are opened by the occupants. The passive v
37、entilation of this building is prior to the HVAC system to reduce cooling and heating load. The atrium with skylight with can improve the natural ventilation, and the cold air from underground ventilation system can cool down the interior passively in summer time, the cooling load will be largely re
38、duced. From the data we collected in late June and early July, the average temperature of the office building with improved natural ventilation was below 79 F (26C) in most of the days and only about fifteen days in summer time needs mechanical cooling inputs, which can largely reduce the energy con
39、sumption of cooling. Table 3. Indoor control design parameters Summer set temperature Winter set temperature Humidity Wind speed (F) (C) (F) (C) （ %） （ m/s） Office 79 26 68 20 60 0.2 Meeting room 79 26 68 20 60 0.2 Exhibition 79 26 64 18 60 0.2 Restroom 79 26 61 16 60 0.2 Lighting control Undergroun
40、d UDI 56% First floor UDI 73% Second floor UDI 80% Figure 3 Useful Daylight Illuminance (UDI) simulation result for office and atrium space. The atrium and semi-floor glazing facade can both improve the interior daylighting environment. Sensors are placed to test the illuminance in each office room.
41、 When the illuminance on workplane is over 100 lux, the electrical lighting system is automatically turned off, otherwise is turned on to achieve a good interior lighting environment. Figure 3 shows the daylighting simulation result by useful daylight illuminance (UDI) for the office and public area
42、. Due to the daylighting simulation result and the usage data collected for the first two month, there is almost no need to use the electrical lighting system in office space during daytime. LED energy-saving lamps are used for illumination in all the space to reduce the lighting energy consumption.
43、 Double - Source Heat Pump In the SGZEB the heating and cooling generation is carried out by a double source heat pump (air source and ground source) that exchanges with the underground environment and ground through thirty-two vertical wells of 164 ft (50 m) each. The geothermal heat pump can provi
44、de cooling source which covers the cooling load in summer time. The air in the space of Trombe wall system on the south facade is heated in winter time, together with the heat produced by the geothermal heat pump system, the double-source heat pump can produce heat for the radiant floor in each flat
45、. The installed Air Treatment Unit (ATU) is linked to the geothermal heat pump. The thermal energy recovered avoids the inner air heat or cool dispersion before the expulsion, and avoids thermal waste. The outer air is also naturally pre-conditioned through an underground duct of about 374 ft (114 m
46、) before getting to the ATU. Renewable energy The electricity consumption has also been covered by the installation of a photovoltaic (PV) system on the roof and south faade of the building. The reflectance is 10% for PV battery, and 9% for the glass. The photoelectric conversion rate for roof PV sy
47、stem is 15%, for south wall PV system is 11%. The area of roof PV system is 1,561 ft2 (145 m2) and the area of south wall PV system is 1,549 ft2 (144 m2). The PV system produced 152349 kBtu per year (44649 kWh per year) totally. The area of green roof is 2303 ft2 (214 m2), which is 52.2% of the tota
48、l roof area and achieves the goal of 30% by Green building rating standard (GB50378-2006). Figure 4 (a) Plan of roof PV system, and (b) aerial view of the SGZEB On stair case roof there are three flat plane solar thermal collectors. The total area is 142 ft2 (13.2 m2). The thermal collectors provide
49、 7731 ft3 (219 m3) domestic hot water per year, which covers the 100% of the total domestic hot water for the guest room on the first floor. Since the thermal collectors integrate or completely replace (according to the season) the heat pump in the production of domestic hot water. The hot water in the re-circulation system can get into the users immediately avoiding water wastes. An indirect active system is used: a pump is employed to circulate a Heat Transfer Fluid (HTF) between the collector and a st
