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Simulation and Analysis of the Energy Consumption for Public Buildings in Different Climate Regions of China
Available online at www.sciencedirect.com
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 2940–2947
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
Simulation and Analysis of the Energy Consumption for Public Buildings in Different Climate Regions of China Bingwen Zhao, Lijuan Qi*, Ting Yang School of Civil Engineering and Architecture, Zhejiang Sci-Tech University, Hangzhou, 310018, China
Abstract Based on a public building in China, this paper built a benchmark model and analyzed the influence of main thermal performance of building envelopes on energy consumption in different climatic regions by EnergyPlus. The results showed that in the order of hot summer and warm winter region, hot summer and cold winter region, cold region, severe cold region, the energy-saving effect was getting better and better with the increase of roof insulation, exterior wall insulation and exterior window insulation. If SHGC of exterior window was reduced, building energy consumption decreased in hot summer and warm winter region, hot summer and cold winter region, but it increased in cold region and severe cold region. For hot summer and warm winter region, hot summer and cold winter region, the factors that affected energy consumption was as follows: SHGC > Kwin > Kwal > Kro, for cold region and severe cold region, it was as follows: Kwin > Kwal > SHGC > Kro. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Ltd. committee of the 10th International Symposium on Heating, Ventilation and Air Peer-review under responsibility of Elsevier the scientific Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Air Conditioning. Keywords:Different climatic regions; Building envelope; Public building; Energy simulation; EnergyPlus
1. Introduction At present, the world is facing energy shortages, environmental pollution and other issues. In China, since 1980s, because of the rapid economic development, urbanization and industrialization, it has greatly promoted the development of construction industry, which causes more and more building energy consumption. It was reported that the building energy consumption accounted for about 1/3 of the total social energy consumption. In 2014, the * Corresponding author. Tel.: +8615061746620. E-mail address:[email protected].
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.110
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total building area was about 56.1 billion m2, of which the public building area was about 10.7 billion m2, the total energy consumption of public buildings (excluding heating in the North) was 0.235 billion tce, accounted for 27% of total building energy consumption. From 2001 to 2014, the unit energy consumption of public buildings increased from 16.8 kgce/m2 to 21.9 kgce/m2, the energy consumption intensity increased by about 30% [1]. In order to solve the contradiction between energy supply and demand, and achieve the strategic goal of China's sustainable development, building energy conservation is imperative. China, with a vast territory, has the large span of latitude and longitude, and the climatic distribution is obviously different. According to the climate characteristics, China can be divided into five climatic zones: hot summer and cold winter region, hot summer and warm winter region, cold region, severe cold region and temperate region [2]. Therefore, considering Chinese situation, the influence of climate factors must be taken into account when analyzing the building energy consumption. Taking a public building as the benchmark model, this paper selected 5 cities with relatively good economic strength in hot summer and cold winter region, hot summer and warm winter region, cold region and severe cold region ( Because the requirement of air conditioning is relatively low in temperate region, so this paper didn’t discuss this region), then analyzed the influence of main thermal performance of building envelopes on energy consumption in different climate conditions by EnergyPlus. 2. Methods 2.1. Simulation analysis method EnergyPlus is a whole building energy analysis tool, developed by Department of energy, USA and Lawrence Berkeley National Laboratory. At present, many scholars had analyzed the energy consumption of public buildings by this software, like school buildings [3-5], office buildings [6,7], shopping malls [8,9] and so on. EnergyPlus is suitable for analysis and simulation, and the results are reliable. 2.2. Contrastive analysis This paper referenced to the idea of controlling variable method when analyzed the influence of main thermal performance of roofs, exterior walls and exterior windows. In each time, only one factor was changed and other factors remained constant, then it discussed the influence of this variable on building energy consumption in different climatic regions quantitatively. Finally, it compared and analyzed the influence of each factor on energy consumption in the same climate region. 3. Results 3.1. Benchmark building This benchmark building (Fig.1) was a public building with the total height of 22 stories. The 1-7 floors were for shopping, the weekends and holidays were still used as usual. The 8-22 floors were offices, the usage rate would reduce at lunch time in weekdays and it was closed on weekends and holidays. The variable refrigerant flow air conditioning system was used in this building, and the air conditioning area was 54,319 m2, the indoor design temperature was 25℃in summer and 20℃ in winter. Table 1 shows the information of building envelopes.
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Fig. 1. The elevation drawing of benchmark building. Table 1. The thermal performance of building envelopes. Name
Direction
Heat transfer coefficient（W/(m2•K)）
East Exterior wall
West South
Window-wall ratio
SHGC
0.65 1.11
North
0.66 0.72 0.66
Roof
0.49
Exterior window
2.5
0.5
3.2. Design parameter Referring to the national code and standard [2,10], this paper selected Nanning, Hangzhou, Beijing, Changchun and Harbin as the representative cities in hot summer and warm winter region, hot summer and cold winter region, cold region, severe cold A/B region and severe cold C region. Table 2 shows the air conditioning periods and the main index to distinguish these regions. Table 1. The information of representative cities. City Nanning Hangzhou
Main index to distinguish regions The average temperature of the coldest month >10℃; The average temperature of the hottest month is 25~29℃. The average temperature of the coldest month is 0~10℃; The average temperature of the hottest month is 25~30℃.
Heating date
Cooling date
12/17—3/4
4/6—11/10
11/8—4/16
5/8—10/3
Beijing
The average temperature of the coldest month is 0~ -10℃.
10/12—4/18
5/8—9/15
Changchun
The average temperature of the coldest month ≤ -10℃.
9/16—5/16
6/12—8/29
Harbin
The average temperature of the coldest month ≤ -10℃.
9/12—5/18
6/2—8/23
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3.3. Annual energy consumption of benchmark building According to Fig.2, with the same construction conditions, the energy consumption was different in different climatic regions. Took Nanning as an example, the building energy consumption in this city was mainly fans, equipment, lighting and cooling. The proportion of heating was very small, so in this region, heating needn’t be considered. However, Harbin, in the severe cold region, there was a lot of energy consumption of heating but a small proportion of cooling, the main building thermal design in Harbin was enhancing insulation in winter, without considering the heat protection in summer.
Fig. 2. Annual energy consumption per unit area in different cities.
There were many factors that affect building energy consumption, such as indoor design temperature, energy use habits of people, equipment performance, insulation performance of building envelopes, etc [11-14]. This paper mainly analyzed the influence of the main thermal performance of roofs, exterior windows and exterior walls on energy consumption in different climatic regions 3.4. Heat transfer coefficient of roofs The change rate of thermal performance (CRTP) of building envelopes was given in this paper, for example, CRTP = 10% meant the thermal performance like heat transfer coefficient was reduced by 10%, which was 90% of benchmark’s now. CRTP = -10% meant it increased by 10%, which was 110% of benchmark’s. With the decrease of roof heat transfer coefficient (Kro) (the increase of CRTP), the energy-saving rate of building energy consumption increased (Fig.3(a)), the rate was increasing in the order of hot summer and warm winter region (Nanning), hot summer and cold winter region (Hangzhou), cold region (Beijing), severe cold A/B region (Changchun) and severe cold C region (Harbin) (This sequence was the climate region sequence mentioned below in this paper). For instance, when CRTP was 50%, energy-saving rate of total building energy consumption in Nanning was 0.244%, but it was 1.104% in Harbin. However, the total energy consumption in Harbin was higher than in Nanning, even there was the same rate, the energy-saving quantity was more in Harbin. Therefore, roof insulation would take better energy-saving effect in cold regions than in warm regions. 3.5. Heat transfer coefficient of exterior walls With the improvement of exterior wall insulation, the energy-saving rate was increasing with the climate region sequence (Fig.3 (b)). In the same region, when the heat transfer coefficient of exterior walls (Kwal) was from 1.568W/ (m2•K) to 0.336 W/ (m2•K), the energy-saving rate got higher if Kwal was reduced the same percentage. In China, building energy-saving effect became more and more obvious with the increase of exterior wall insulation
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and the order of regions mentioned above. If economic factors were not taken into account, better exterior wall insulation meant higher energy-saving rate.
Fig. 3. (a) energy-saving rate of total building energy consumption (roof); (b) energy-saving rate of total building energy consumption (exterior wall).
3.6. Heat transfer coefficient of exterior windows According to Fig.4 (a), except for hot summer and warm winter region, with the climate region sequence, building energy consumption increased with the increase of the heat transfer coefficient of exterior windows (Kwin), and the decline of energy-saving rate was increasing in this sequence. Moreover, if Kwin was reduced by 5%, energy consumption could be reduced by 1% - 1.5% in cold region and severe cold region. With the increase of Kwin, the heating energy-saving rate decreased, and these cities had similar trends excluding Nanning. For cooling energy-saving rate, except for Beijing, it decreased first and then increased. When Kwin< 1.75 W/(m2•K), with the increasing of Kwin, although heat dissipating capacity continued to increase, but it was still less than the heat obtained from outside, cooling energy consumption was increasing. When Kwin> 1.75 W/(m2•K), heat dissipating capacity was more than heat obtained from outside, cooling energy consumption was reduced. When 1.75 W/(m2•K) ≤ Kwin ≤ 2.75W/(m2•K), the smaller the Kwin, the worse the cooling condition in summer. When Kwin< 1.75 W/(m2•K), it could reduce cooling energy consumption effectively if we enhanced window insulation. On the whole, with the climate region sequence, energy-saving effect could be better and better if we enhanced exterior window insulation.
Fig. 4. (a) energy-saving rate of total building energy consumption (exterior window); (b) energy-saving rate of total building energy consumption (SHGC).
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3.7. Solar heat gain coefficient of exterior windows According to the curve shown in Fig.4 (b), the energy consumption in Nanning and Hangzhou decreased, but it increased in Beijing, Changchun and Harbin, when solar heat gain coefficient (SHGC) of exterior windows increased. In Nanning and Hangzhou, the total energy consumption was dominated by cooling, the heat gain through window from outside was high, which increased cooling energy consumption. Increasing the exterior window shading could improve heat protection in summer, although the indoor heat gain was reduced to some extent in winter, but the total energy consumption still decreased. On the contrary, in cold region and severe cold region, heating was more important, higher SHGC was favorable. Therefore, for shading measures of exterior window, the design should be combined with geographical factors and climate environment. 4. Discussion Analyzed the effects of roof insulation, exterior wall insulation, exterior window insulation and shading measures on public buildings with large window-wall ratio in different regions. Fig.5 shows the energy-saving rate of total building energy consumption when they increased or decreased the same percentage. The result showed that the main thermal performance of each building envelope had different impacts on energy consumption in different climate regions. For hot summer and warm winter region, hot summer and cold winter region, the thermal performance about the building envelopes that affected energy consumption was as follows: SHGC of exterior window > Kwin> Kwal > Kro, for cold region and severe cold region, it was as follows: Kwin> Kwal> SHGC of exterior window > Kro.
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Fig. 5. (a) the influence of various factors on building energy consumption in Nanning; (b) the influence of various factors on building energy consumption in Hangzhou; (c) the influence of various factors on building energy consumption in Beijing; (d) the influence of various factors on building energy consumption in Changchun; (e) the influence of various factors on building energy consumption in Harbin.
5. Conclusions For the order of hot summer and warm winter region, hot summer and cold winter region, cold region, severe cold A/B region and severe cold C region, when roof insulation was enhanced, the effect of building energy conservation would be better and better. The energy-saving rate increased with the decrease of Kwal and the climate region sequence. Energy-saving rate got higher if Kwal decreased the same percentage in the same region. Except for hot summer and warm winter region, energy-saving quantity was increasing with the decrease of Kwin. For cold region and severe cold region, the building energy consumption could be reduced by 1%-1.5% if Kwin was reduced by 5%. With the decrease of SHGC of exterior window, building energy consumption decreased in hot summer and warm winter region, hot summer and cold winter region, but it increased in cold region and severe cold region. For hot summer and warm winter region, hot summer and cold winter region, the thermal performance about the building envelopes that affected energy consumption was as follows: SHGC of exterior window > Kwin> Kwal> Kro,for cold region and severe cold region, it was as follows: Kwin> Kwal> SHGC of exterior window > Kro. In China, building energy-saving work can’t be copied blindly or just be the technology stack, it must be combined with their own specific circumstances and local conditions. To the regions where are dominated by cooling in summer, we can enhance exterior window shading measures and strengthen its insulation.However, to the regions where heating is more important, we can strengthen insulation of exterior windows and walls, but reduce exterior window shading.Whatever, it is not so necessary to strengthen roof insulation in all regions. Acknowledgements This paper was funded by Ministry of Housing and Urban-Rural Development of the People’s Republic of China (MOHURD) about energy use and energy consumption of residential buildings in Zhejiang (2010-R1-7), the projects in Zhejiang Sci-Tech University about postgraduate course construction (YKC-Z15024) and the course construction of the flipped classroom demonstration course based on SPOC (spoc1404). References [1] Building energy conservation research center, Tsinghua University. 2016 annual report on China building energy efficiency. China Architecture and Building Press, Bei Jing, 2016. [2] Ministry of Housing and Urban-Rural Development of the People's Republic of China. Thermal design code for civil builing, 2016. (GB 50176-2016). [3] G. Rospi, N. Cardinale, F. Intini, et al. Analysis of energy consumption of different typologies of school buildings in the city of matera (southern Italy), J. Energy Procedia. 82(2015)512-518.
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[4] T.E. Jiru. Combining HVAC energy conservation measures to achieve energy savings over standard requirements, J. Energy and Buildings. 73(2014) 171–175. [5] C. Zhang. Energy performance simulation study on VAV air condition system at SPSUcampus office building with energyplus, J. Applied Mechanics and Materials. 361-363(2013) 249-252. [6] A. Boyano, P. Hernandez, O. Wolf. Energy demands and potential savings in European office Buildings: Case studies based on EnergyPlus simulations, J. Energy and Buildings. 65(10)(2013) 19-28. [7] Y.S. Ko, T. No. A case study on the verification of passive office energy performance comparing actual energy consumption to simulation result, J. Applied Mechanics and Materials. 361-363(2013) 427-430. [8] S. Zheng, H. Liang．Simulation and study on energy-saving of air-conditioning system energy consumption of a shopping plaza in Xi'an, J. Building Energy and Environment. 33 (3) (2014) 38-41． [9] G.C. da Graca, N.R. Martins, C.S. Horta. Thermal and airflow simulation of a naturally ventilated shopping mall, J. Energy and Buildings, 50 (2012) 177–188. [10] Ministry of Housing and Urban-Rural Development of the People's Republic of China. Design standard for energy efficiency of public buildings, 2015. (GB50189-2015). [11] C. Li, J. Tan, T. Chow, et al. Experimental and theoretical study on the effect of window films on building energy consumption, J. Energy and Buildings. 102(2015) 129-138. [12] S. Yu, Y. Cui, X. Xu, et al. Impact of civil envelope on energy consumption based on energyplus, J. Procedia Engineering. 121(2015) 15281534. [13] F. Liu, W. Ma. Survey of residential energy usage behavior and energy consumption in Shenzhen, J. Building Energy Efficiency. 43(288) (2015)108-113． [14] O. Kaynakli. A review of the economical and optimum thermal insulation thickness for building applications, J. Renewable and Sustainable Energy Reviews. 16(1) (2012) 415-425.
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 2940–2947
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
Simulation and Analysis of the Energy Consumption for Public Buildings in Different Climate Regions of China Bingwen Zhao, Lijuan Qi*, Ting Yang School of Civil Engineering and Architecture, Zhejiang Sci-Tech University, Hangzhou, 310018, China
Abstract Based on a public building in China, this paper built a benchmark model and analyzed the influence of main thermal performance of building envelopes on energy consumption in different climatic regions by EnergyPlus. The results showed that in the order of hot summer and warm winter region, hot summer and cold winter region, cold region, severe cold region, the energy-saving effect was getting better and better with the increase of roof insulation, exterior wall insulation and exterior window insulation. If SHGC of exterior window was reduced, building energy consumption decreased in hot summer and warm winter region, hot summer and cold winter region, but it increased in cold region and severe cold region. For hot summer and warm winter region, hot summer and cold winter region, the factors that affected energy consumption was as follows: SHGC > Kwin > Kwal > Kro, for cold region and severe cold region, it was as follows: Kwin > Kwal > SHGC > Kro. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Ltd. committee of the 10th International Symposium on Heating, Ventilation and Air Peer-review under responsibility of Elsevier the scientific Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Air Conditioning. Keywords:Different climatic regions; Building envelope; Public building; Energy simulation; EnergyPlus
1. Introduction At present, the world is facing energy shortages, environmental pollution and other issues. In China, since 1980s, because of the rapid economic development, urbanization and industrialization, it has greatly promoted the development of construction industry, which causes more and more building energy consumption. It was reported that the building energy consumption accounted for about 1/3 of the total social energy consumption. In 2014, the * Corresponding author. Tel.: +8615061746620. E-mail address:[email protected].
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.110
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total building area was about 56.1 billion m2, of which the public building area was about 10.7 billion m2, the total energy consumption of public buildings (excluding heating in the North) was 0.235 billion tce, accounted for 27% of total building energy consumption. From 2001 to 2014, the unit energy consumption of public buildings increased from 16.8 kgce/m2 to 21.9 kgce/m2, the energy consumption intensity increased by about 30% [1]. In order to solve the contradiction between energy supply and demand, and achieve the strategic goal of China's sustainable development, building energy conservation is imperative. China, with a vast territory, has the large span of latitude and longitude, and the climatic distribution is obviously different. According to the climate characteristics, China can be divided into five climatic zones: hot summer and cold winter region, hot summer and warm winter region, cold region, severe cold region and temperate region [2]. Therefore, considering Chinese situation, the influence of climate factors must be taken into account when analyzing the building energy consumption. Taking a public building as the benchmark model, this paper selected 5 cities with relatively good economic strength in hot summer and cold winter region, hot summer and warm winter region, cold region and severe cold region ( Because the requirement of air conditioning is relatively low in temperate region, so this paper didn’t discuss this region), then analyzed the influence of main thermal performance of building envelopes on energy consumption in different climate conditions by EnergyPlus. 2. Methods 2.1. Simulation analysis method EnergyPlus is a whole building energy analysis tool, developed by Department of energy, USA and Lawrence Berkeley National Laboratory. At present, many scholars had analyzed the energy consumption of public buildings by this software, like school buildings [3-5], office buildings [6,7], shopping malls [8,9] and so on. EnergyPlus is suitable for analysis and simulation, and the results are reliable. 2.2. Contrastive analysis This paper referenced to the idea of controlling variable method when analyzed the influence of main thermal performance of roofs, exterior walls and exterior windows. In each time, only one factor was changed and other factors remained constant, then it discussed the influence of this variable on building energy consumption in different climatic regions quantitatively. Finally, it compared and analyzed the influence of each factor on energy consumption in the same climate region. 3. Results 3.1. Benchmark building This benchmark building (Fig.1) was a public building with the total height of 22 stories. The 1-7 floors were for shopping, the weekends and holidays were still used as usual. The 8-22 floors were offices, the usage rate would reduce at lunch time in weekdays and it was closed on weekends and holidays. The variable refrigerant flow air conditioning system was used in this building, and the air conditioning area was 54,319 m2, the indoor design temperature was 25℃in summer and 20℃ in winter. Table 1 shows the information of building envelopes.
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Fig. 1. The elevation drawing of benchmark building. Table 1. The thermal performance of building envelopes. Name
Direction
Heat transfer coefficient（W/(m2•K)）
East Exterior wall
West South
Window-wall ratio
SHGC
0.65 1.11
North
0.66 0.72 0.66
Roof
0.49
Exterior window
2.5
0.5
3.2. Design parameter Referring to the national code and standard [2,10], this paper selected Nanning, Hangzhou, Beijing, Changchun and Harbin as the representative cities in hot summer and warm winter region, hot summer and cold winter region, cold region, severe cold A/B region and severe cold C region. Table 2 shows the air conditioning periods and the main index to distinguish these regions. Table 1. The information of representative cities. City Nanning Hangzhou
Main index to distinguish regions The average temperature of the coldest month >10℃; The average temperature of the hottest month is 25~29℃. The average temperature of the coldest month is 0~10℃; The average temperature of the hottest month is 25~30℃.
Heating date
Cooling date
12/17—3/4
4/6—11/10
11/8—4/16
5/8—10/3
Beijing
The average temperature of the coldest month is 0~ -10℃.
10/12—4/18
5/8—9/15
Changchun
The average temperature of the coldest month ≤ -10℃.
9/16—5/16
6/12—8/29
Harbin
The average temperature of the coldest month ≤ -10℃.
9/12—5/18
6/2—8/23
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3.3. Annual energy consumption of benchmark building According to Fig.2, with the same construction conditions, the energy consumption was different in different climatic regions. Took Nanning as an example, the building energy consumption in this city was mainly fans, equipment, lighting and cooling. The proportion of heating was very small, so in this region, heating needn’t be considered. However, Harbin, in the severe cold region, there was a lot of energy consumption of heating but a small proportion of cooling, the main building thermal design in Harbin was enhancing insulation in winter, without considering the heat protection in summer.
Fig. 2. Annual energy consumption per unit area in different cities.
There were many factors that affect building energy consumption, such as indoor design temperature, energy use habits of people, equipment performance, insulation performance of building envelopes, etc [11-14]. This paper mainly analyzed the influence of the main thermal performance of roofs, exterior windows and exterior walls on energy consumption in different climatic regions 3.4. Heat transfer coefficient of roofs The change rate of thermal performance (CRTP) of building envelopes was given in this paper, for example, CRTP = 10% meant the thermal performance like heat transfer coefficient was reduced by 10%, which was 90% of benchmark’s now. CRTP = -10% meant it increased by 10%, which was 110% of benchmark’s. With the decrease of roof heat transfer coefficient (Kro) (the increase of CRTP), the energy-saving rate of building energy consumption increased (Fig.3(a)), the rate was increasing in the order of hot summer and warm winter region (Nanning), hot summer and cold winter region (Hangzhou), cold region (Beijing), severe cold A/B region (Changchun) and severe cold C region (Harbin) (This sequence was the climate region sequence mentioned below in this paper). For instance, when CRTP was 50%, energy-saving rate of total building energy consumption in Nanning was 0.244%, but it was 1.104% in Harbin. However, the total energy consumption in Harbin was higher than in Nanning, even there was the same rate, the energy-saving quantity was more in Harbin. Therefore, roof insulation would take better energy-saving effect in cold regions than in warm regions. 3.5. Heat transfer coefficient of exterior walls With the improvement of exterior wall insulation, the energy-saving rate was increasing with the climate region sequence (Fig.3 (b)). In the same region, when the heat transfer coefficient of exterior walls (Kwal) was from 1.568W/ (m2•K) to 0.336 W/ (m2•K), the energy-saving rate got higher if Kwal was reduced the same percentage. In China, building energy-saving effect became more and more obvious with the increase of exterior wall insulation
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and the order of regions mentioned above. If economic factors were not taken into account, better exterior wall insulation meant higher energy-saving rate.
Fig. 3. (a) energy-saving rate of total building energy consumption (roof); (b) energy-saving rate of total building energy consumption (exterior wall).
3.6. Heat transfer coefficient of exterior windows According to Fig.4 (a), except for hot summer and warm winter region, with the climate region sequence, building energy consumption increased with the increase of the heat transfer coefficient of exterior windows (Kwin), and the decline of energy-saving rate was increasing in this sequence. Moreover, if Kwin was reduced by 5%, energy consumption could be reduced by 1% - 1.5% in cold region and severe cold region. With the increase of Kwin, the heating energy-saving rate decreased, and these cities had similar trends excluding Nanning. For cooling energy-saving rate, except for Beijing, it decreased first and then increased. When Kwin< 1.75 W/(m2•K), with the increasing of Kwin, although heat dissipating capacity continued to increase, but it was still less than the heat obtained from outside, cooling energy consumption was increasing. When Kwin> 1.75 W/(m2•K), heat dissipating capacity was more than heat obtained from outside, cooling energy consumption was reduced. When 1.75 W/(m2•K) ≤ Kwin ≤ 2.75W/(m2•K), the smaller the Kwin, the worse the cooling condition in summer. When Kwin< 1.75 W/(m2•K), it could reduce cooling energy consumption effectively if we enhanced window insulation. On the whole, with the climate region sequence, energy-saving effect could be better and better if we enhanced exterior window insulation.
Fig. 4. (a) energy-saving rate of total building energy consumption (exterior window); (b) energy-saving rate of total building energy consumption (SHGC).
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3.7. Solar heat gain coefficient of exterior windows According to the curve shown in Fig.4 (b), the energy consumption in Nanning and Hangzhou decreased, but it increased in Beijing, Changchun and Harbin, when solar heat gain coefficient (SHGC) of exterior windows increased. In Nanning and Hangzhou, the total energy consumption was dominated by cooling, the heat gain through window from outside was high, which increased cooling energy consumption. Increasing the exterior window shading could improve heat protection in summer, although the indoor heat gain was reduced to some extent in winter, but the total energy consumption still decreased. On the contrary, in cold region and severe cold region, heating was more important, higher SHGC was favorable. Therefore, for shading measures of exterior window, the design should be combined with geographical factors and climate environment. 4. Discussion Analyzed the effects of roof insulation, exterior wall insulation, exterior window insulation and shading measures on public buildings with large window-wall ratio in different regions. Fig.5 shows the energy-saving rate of total building energy consumption when they increased or decreased the same percentage. The result showed that the main thermal performance of each building envelope had different impacts on energy consumption in different climate regions. For hot summer and warm winter region, hot summer and cold winter region, the thermal performance about the building envelopes that affected energy consumption was as follows: SHGC of exterior window > Kwin> Kwal > Kro, for cold region and severe cold region, it was as follows: Kwin> Kwal> SHGC of exterior window > Kro.
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Fig. 5. (a) the influence of various factors on building energy consumption in Nanning; (b) the influence of various factors on building energy consumption in Hangzhou; (c) the influence of various factors on building energy consumption in Beijing; (d) the influence of various factors on building energy consumption in Changchun; (e) the influence of various factors on building energy consumption in Harbin.
5. Conclusions For the order of hot summer and warm winter region, hot summer and cold winter region, cold region, severe cold A/B region and severe cold C region, when roof insulation was enhanced, the effect of building energy conservation would be better and better. The energy-saving rate increased with the decrease of Kwal and the climate region sequence. Energy-saving rate got higher if Kwal decreased the same percentage in the same region. Except for hot summer and warm winter region, energy-saving quantity was increasing with the decrease of Kwin. For cold region and severe cold region, the building energy consumption could be reduced by 1%-1.5% if Kwin was reduced by 5%. With the decrease of SHGC of exterior window, building energy consumption decreased in hot summer and warm winter region, hot summer and cold winter region, but it increased in cold region and severe cold region. For hot summer and warm winter region, hot summer and cold winter region, the thermal performance about the building envelopes that affected energy consumption was as follows: SHGC of exterior window > Kwin> Kwal> Kro,for cold region and severe cold region, it was as follows: Kwin> Kwal> SHGC of exterior window > Kro. In China, building energy-saving work can’t be copied blindly or just be the technology stack, it must be combined with their own specific circumstances and local conditions. To the regions where are dominated by cooling in summer, we can enhance exterior window shading measures and strengthen its insulation.However, to the regions where heating is more important, we can strengthen insulation of exterior windows and walls, but reduce exterior window shading.Whatever, it is not so necessary to strengthen roof insulation in all regions. Acknowledgements This paper was funded by Ministry of Housing and Urban-Rural Development of the People’s Republic of China (MOHURD) about energy use and energy consumption of residential buildings in Zhejiang (2010-R1-7), the projects in Zhejiang Sci-Tech University about postgraduate course construction (YKC-Z15024) and the course construction of the flipped classroom demonstration course based on SPOC (spoc1404). References [1] Building energy conservation research center, Tsinghua University. 2016 annual report on China building energy efficiency. China Architecture and Building Press, Bei Jing, 2016. [2] Ministry of Housing and Urban-Rural Development of the People's Republic of China. Thermal design code for civil builing, 2016. (GB 50176-2016). [3] G. Rospi, N. Cardinale, F. Intini, et al. Analysis of energy consumption of different typologies of school buildings in the city of matera (southern Italy), J. Energy Procedia. 82(2015)512-518.
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