The application of solar technologies in building energy efficiency: BISE design in solar-powered residential buildings

The application of solar technologies in building energy efficiency: BISE design in solar-powered residential buildings

Technology in Society 38 (2014) 111–118 Contents lists available at ScienceDirect Technology in Society journal homepage: www.elsevier.com/locate/te...

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Technology in Society 38 (2014) 111–118

Contents lists available at ScienceDirect

Technology in Society journal homepage: www.elsevier.com/locate/techsoc

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The application of solar technologies in building energy efficiency: BISE design in solar-powered residential buildings Li Yang a, Bao-jie He b, *, Miao Ye b a College of Architecture & Urban Planning, Tongji University; Institute for Advanced Study in Architecture and Urban Planning, Key Laboratory of Ecology and Energy Saving Study of Dense Habitat (Tongji University), Ministry of Education, 1239 Si Ping Road, Shanghai 200092, PR China b School of Environment and Architecture, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 23 October 2013 Received in revised form 2 March 2014 Accepted 5 March 2014

At present, building energy consumption is growing rapidly in China and it accounts for about 30% of the total energy consumption. Solar energy, as a type of renewable energy, will greatly alleviate the pressure of the building energy consumption if it is widely used in residential buildings. Firstly, this paper briefly introduced the characteristics and distribution of solar energy resources in China. Secondly, this paper summarized the three types of solar energy utilization: light-gathering utilization, solar energy photo-thermal utilization and photovoltaic utilization. Among them, photo-thermal technology is suitable for solar-powered residential buildings (SPRBs) in terms of current technology and economy. Thirdly, authors analyzed the passive SPRBs and active SPRBs, where the active SPRBs are more intelligent due to its flexibility and controllability. Based on the above analysis, to realize the harmony between solar technologies and building appearance, authors put forward building integrated solar energy (BISE) design in the consideration of technology and aesthetics. The development and application of solar technologies in residential buildings embodies the concepts of energy conservation, environmental protection and sustainable development, and it will promote the development of building energy efficiency. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Solar technologies Solar-powered residential buildings Passive SPRBs Active SPRBs BISE design

1. Introduction Energy is one of the material motive powers to promote social and economic development, energy supply shortages and its potential threat will directly or indirectly affect the development of national economy and economic security. So energy has always been an important theme of sustainable development. With speeding urbanization and new rural construction, building area is rising at an annual

* Corresponding author. 711 Room, 9 Apartment, South Campus, 516 Jungong Road, Yangpu District, Shanghai, PR China. Tel.: þ86 0 18818261969; fax: þ86 0 2133626063. E-mail addresses: [email protected] (L. Yang), [email protected] 163.com (B.-j. He), [email protected] (M. Ye). http://dx.doi.org/10.1016/j.techsoc.2014.03.002 0160-791X/Ó 2014 Elsevier Ltd. All rights reserved.

rate of 2 billion m2 and the total building area has exceeded 40 m2 [32]. Meanwhile, the proportion of building energy consumption in the total energy consumption has risen from 10% in the late 1970s to about 30% in 2010, about a tripling with an annual growth of 5.64% [10,13,21,30]. The situation of energy consumption in 2010 is shown in Fig. 1. In terms of energy demand, supply and consumption, coal plays a dominant part in China, making up 70 percent of its fuel consumption. So the huge energy consumption in building industry not only consumes a lot of non-renewable resource but also contributes the emissions of harmful substances into the atmosphere. Statistics from International Energy Agency (IEA) show that the CO2 emission in 2010 exceeded 7.5 billion tons in China, which is largely generated from coal and accounts for 25% of the global emissions [25].

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Fig. 1. The present situation of energy consumption in China.

Meanwhile, the urban Particulates Matter (PM) in 65% cities in China has exceed the national standard and SO2 concentration in many cities has exceeded national second class emission standard. In addition, according to the energy reserves and development intensity calculation, the world fossil energy on average less than one hundred years development time already [7,15,20,27]. To solve the problem caused by environmental pollution and energy shortage, the utilization and promotion of renewable energy in residential buildings has been paid more attentions during these years. Solar energy, as one kind of thermal radiation energy, is also a kind of non-pollution clean energy. For the development and utilization of renewable energy, solar energy has become one of the important research projects for energy saving and environmental protection all over the world. Until now, great progress has been made and the development of solar energy has entered the practical stage. Nowadays, China appears to be facing the challenges of population expansion and an energy shortage. With rich solar resources in most areas of China, it is an opportunity to develop solar energy and to promote energy saving buildings, which fully reflects the concept of sustainable development and green ecological energy-saving. In the second section, authors have briefly introduced the characteristics and distribution of the solar energy resources in China; meanwhile, the main forms of solar energy utilization are summarized. Next, the utilization of photo-thermal technology in solar-powered residential buildings (SPRBs) is analyzed from the perspective of current technology and economic benefit. In the fourth section, based on the analysis of active SPRBs and passive SPRBs, the authors have put forward the building integrated solar energy (BISE) design to integrate technology and aesthetics, aiming to realize the harmony between solar technologies and building appearance. This approach alleviates some of the biggest challenges to solar energy adoption and provides a path forward for this technology.

permanent resources on the earth. Compared with the conventional energy, solar energy has many advantages as following: inexhaustible, clean, safe, reliable and pollution free. And at the same time, there are two main deficiencies in this renewable energy. The first one is dispersion, which is caused by the low solar energy flux density. Near the tropic of cancer, the mean solar energy flux density is 200 W per day, but only half of that in winter and about 1/5 of that in cloudy day. Therefore, in the utilization of solar energy, it is necessary to provide a set of collection and conversion equipment with large area to get enough switching power, but the cost is high. Another disadvantage of solar energy is discontinuity and instability, and it is caused by the natural conditions, such as day and night, season, geographic latitude and altitude, and it is influenced by the random factors, such as the weather. So the discontinuous and unstable solar irradiance will increase the difficulty to the large-scale application of solar energy [6,8,9]. According to statistics, the annual total solar energy is 1  1018 kW h, which is equivalent to 13 trillion tons of standard coal. Meanwhile, it is about 1000 times the proven oil reserves, and it is ten thousand times more than total annual energy consumption of the world. China is located in the northern hemisphere, and spans of north-south and east-west are both more than 5000 km. The unique geographical features bring abundant solar energy resources for China. Statistics from the long term observation in about 700 meteorological stations in China show that the annual solar radiation amount per square meter all over the country is between 3.3  106 kJ to 8.4  106 kJ, and the mean value is 5.9  106 kJ [17,26,31]. At the same time, the annual total solar energy resource is equivalent to 1.7 trillion tons of standard coal, so there is great potential for solar energy development and utilization in China. Fig. 2 shows the distribution of solar energy resources in China. The high value center and low value center of solar energy both lie between about 22 and 35 north latitude, and the high value center located on Qinghai–Tibet Plateau. Seen from the locations of annual total solar radiation, the amount in western region is higher than it in eastern region. At the same time, the amount in southern region is basically lower than it in northern region except Tibet and Xinjiang. In addition, we can see from Table 1 the area where the annual total solar radiation per square meter is larger than 5000 MJ and the sunshine hours are larger than 2200 h accounts for more than 2/3 of the national territory area of China. Especially in the northern China and northwest China, the sufficient sunshine provides good conditions for the utilization of solar energy resource. So it will meet the national energy demand if 1% of the annual total solar radiation is converted to available resource in China [33]. 2.2. Main forms for solar energy utilization

2. The situation of solar energy 2.1. The characteristics of solar energy Solar energy, as the most important basic energy of all sorts of renewable ones, is the most important abundant

It is well known that energy from the sun reaches the earth in the form of electromagnetic radiation. So many technical problems have to be solved in the process of solar energy utilization. According to the characteristics of the solar energy, there are four main kinds of solar energy

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Fig. 2. The distribution of solar energy resources in China.

technologies as following: solar energy collection, solar energy conversion, solar energy storage and solar energy transmission. And the combination of the above technologies and other related technologies will realize the utilization of solar energy, such as light-gathering utilization, solar energy photo-thermal utilization, photovoltaic utilization and photochemical utilization. Light-gathering utilization is the simplest form for solar energy utilization. The solar radiation is converged by concave mirror to provide sufficient power for receiving surface. This technology is the basis of other technologies,

and the solar cooker in our daily life is a good example of light-gathering utilization. Solar energy photo-thermal utilization is a form that uses heat storage devices to heat thermal storage medium, such as water, gases and walls, then to achieve the purposes of heating water and indoor heating [29]. This method is a kind of relatively simple, economic, environmental and reliable way to improve the building thermal environment. In addition, photo-thermal technology will not increase the burden of power grid, so it is better than other technologies to solve the problem of energy storage. From multiple

Table 1 The assessment of solar energy resource in China. Location class

Annual sunshine hours

Annual total solar radiation (MJ/m2)

Region (provinces, autonomous regions)

Description

1

3200–3300

6680–8400

Northern Ningxia, Northern Gansu, Southern Xinjiang, Western Qinghai, Western Tibet

2

3000–3200

5852–6680

3

2200–3000

5016–5852

4

1400–2000

4180–5016

5

1000–1400

3344–4180

Northern Hebei, Northern Shanxi, Southern Inner Mongolia, Southern Ningxia, Central Gansu, Eastern Qinghai, Southeastern Tibet, Southern Xinjiang Shandong, Henan, Southeastern Hebei, Southern Shanxi, Northern Xinjiang, Jilin, Liaoning, Yunnan, Northern Shanxi, Southeastern Gansu, Southern Guangdong Hunan, Guangxi, Jiangxi, Zhejiang, Hubei, Northern Fujian, Northern Guangdong, Southern Guangdong, Southern Shanxi, Southern Anhui Most areas in Sichuan, Guizhou

This region is the richest in solar resource in China and the annual solar energy is equivalent to 225–285 kg of standard coal. Solar resource is abundant in this region and the annual solar energy is equivalent to 200–225 kg of standard coal. The annual solar energy is equivalent to 170–200 kg of standard coal.

The annual solar energy is equivalent to 140–170 kg of standard coal.

This region is the poorest in solar resource in China and the annual solar energy is equivalent to 115–140 kg of standard coal, but it still has a certain development value

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perspectives, this method is suitable for the current situation of China, and thus it will be promoted and widely used in building energy efficiency. In solar energy photovoltaic utilization, the received solar radiation is converted to electricity by photovoltaic devices. Stand-alone photovoltaic power system is mainly used in the remote areas and dispersed population areas without power grid, but cost of this system is very high. Gird-connected photovoltaic system has been used in the areas with public supply system, and it has higher efficiency and better environmental performance. However, this typical solar utilization has a higher requirement to electrical energy conversion technologies. At present, countries all over the world have put great attention to research and develop photovoltaic devices, and this method has a broad application prospect in the future [1,2,19,22].

In active SPRBs, the receive, conversion and transmit of solar energy are relied on solar heating equipment and power systems, such as solar collectors and solar pipelines. At the same time, once encountered bad weather situations, electricity should be provided as auxiliary energy. Compared with passive SPRBs, active SPRBs are relatively complex and high cost [18]. Based on the above reasons, passive solar energy utilization will be the main way of solar energy utilization in residential buildings in a long time following. For the building layout, the best solar orientation can be obtained by ecological ECOTECT Software via loading the local geographic information, as shown in Fig. 3. In general, the heating surface should be within plus or minus 15 of the best orientation to get the most satisfied solar radiation.

3. Solar-powered residential buildings (SPRBs)

According to the techniques to receive solar energy, the passive SPRBs can be divided into two forms: direct-gain passive SPRBs and thermal heat storage wall passive SPRBs. In the former type, the amount of solar absorption is mainly depended on the residential building layouts and south windows, which are influenced by natural and human factors. In this system, the inner room is a complex of solar heat storage and distribution, so window is a key element in the process of solar utilization. For example, to reduce the heat loss caused by the window, double-layer Low-E (Low emissivity) glasses are always adopted in severe cold areas. In terms of window dimensions, it is conducive to day lighting when window is larger, but correspondingly the heat loss in night will increase,

At current, solar energy photo-thermal system is the main form of solar utilization in residential buildings, and it can be divided into direct utilization and indirect utilization. The direct utilization can be subdivided into passive mode and active mode. Compared with active SPRBs, the passive SPRBs are relatively simple. In the process of heat transfer, the passive SPRBs do not need additional systems and devices, and the efficiency of them are relied on the technical operations and design methods of engineers and architects, such as reasonable building layout, indoor space design, exterior form arrangement, building material selection and appropriate building structure [14].

3.1. Passive SPRBs

Fig. 3. The optimum orientation of solar buildings.

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therefore it is necessary to take some heat preservation measures. In summer, shading measures should be taken into account to prevent much solar radiation getting into interior, such as setting sun shading board. Thermal heat storage wall is a typical method of passive SPRBs, which takes full advantages of the characteristics of south solar radiation. As shown in Fig. 4, the south wall is covered by a layer of glass cover, so an air layer forms between this glass cover and the wall, namely a simple model of thermal heat storage wall. Once the heat wall captures solar energy, they will be transferred onto interior surface of the room [23]. To get the maximum solar heat, a general practice is to coat the inner surface of glass cover with heatabsorbing materials. For work principle, the air in air layer and the adjacent wall will play a role of indoor temperature regulator at different times if they are heated. In the daytime, airs with heat in the glass cover flows into room by the way of air convection via the outlet that connects the inner space and airspace, as shown in Fig. 4. The heated air will gives off heat to fulfill the goal of increasing indoor temperature, and then cold air will go back to airspace to take heat, all above is a completed cycle. The excessive heat will be stored in the wall which has the performance of heat storage if the solar radiation is sufficient during daytime. This technique could provide heat for inner room in night or on cloudy days, so this system could achieve the aim of all-weather heating. Seen from the work principles of passive solar utilization, the performance of heat insulation materials plays a decisive role on the SPRBs. For translucent materials, light transmittance of previous glass is about 65%–80%, but now

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the transmittance of lighting board is above on 90%. For heat storage materials, two methods could increase the storage capacity, the first one is to increase the thickness of the wall and the second is to use better regenerator medium. In addition, setting thermal storage room is also a kind of effective measure, where the gravel could absorb heat when the warm air flow past this room and generate heat to warm interior room in the night, herein this storage room is also an indoor room regulator. Due to simple structure, low investment, high applicability features of passive SPRBs, they are widely used in residential buildings, even in some high-rise public buildings. In these buildings, the double deck glass curtain wall can be considered as a thermal heat storage wall, which not only uses solar energy, but also beautify the building façade. Looking at current situation in China, the passive SPRBs can be promoted on a large scale. On the one hand, energy saving should be taken into consideration in a new residential building construction on the basis of costeffective and energy-efficient. On the other hand, the retrofitting of old buildings which currently are almost high energy consumption buildings in China should reduce the residential heating energy consumption, especially in north China with cold weather and abundant solar energy resources [3,16]. 3.2. Active SPRBs Active SPRBs is a type of building that transport received heat into house with the help of mechanical equipment. Compared with passive SPRBs, the application of active

Fig. 4. Operating principle of solar collecting wall.

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SPRBs is no longer confined to the wall, but extends to the roof and the slope where can accept solar radiation [4]. In addition, the thermal storage room can set when necessary. The combination of heating system and hot water supply systems makes active SPRBs more intelligent. Same with passive SPRBs, building envelope of active SPRBs should have good thermal insulation performance. For solar energy heating system, the heating media (HTM) temperature should be as low as possible, so the radiant floor heating is the most suitable for solar heating system. Air and water are two types of HTM, but each of them has advantages and disadvantages. Hot air collector is cheaper and less heat transfer, but heat transfer power is larger, air duct and heat storage devices occupy a larger space; Solar hot water collector is complex and expensive, but the price reduces in recent years with the development of vacuum tube collector technology. Therefore, given the situation, the development direction of solar heating system is given priority to with solar hot water system [11,28]. Figs. 5–8 show the work principle of active SPRBs. There are two fans in this system, the first one is collector fan, and another is heating fan. When this system depends on solar radiation, as shown in Fig. 5, two fans are running to ensure the air flows through solar collector, and then flow back to the room. In this period, the thermal storage room does not work. In hot air system, the electric fan is used to control air flow. Two electric fans in air controller are all turned to the direction of room when direct heating. At the same time, solar water system can be set at the outlet of solar collector to provide room hot water. It is necessary to store the excessive heat when the heat received by solar collector is surplus, so thermal storage room starts to work. As shown in Fig. 6, collector fan starts and heating fan stops, at the same time, the electric fans access to the room are also turned off. The hot air would flow into thermal storage room to heat gravel layer to realize the goal of store heat until the room is saturated. On cloudy days or rainy days, the thermal room starts to provide heat for inner room. As shown in Fig. 7, the first electric fan in air controller is turned off, the second one is turned on, and the heating fan is started. The cold air in the room

Fig. 5. The solar air heating system (air supply by collector).

Fig. 6. The solar air heating system (air supply from heat storage room).

flows into gravel layer, and back to heating control system to provide indoor space heat. When the heat in thermal room is used up, auxiliary heating system can be started. When heating is not required in summer or the thermal storage room is saturated, solar collector can be used to provide hot water, work principle is shown in Fig. 8. Although work principals in all SPRBs are same, the HTM are different, some use water as HTM, and some use air. When water is used as media, the volumes of devices will greatly reduce under the same thermal effect. Meanwhile, it could share the same heating system with other energy resources, which will be another advantage of heat media. 4. Building integrated solar energy (BISE) In terms of ecological energy-saving and green environmental protection, to promote the use of solar energy rather than fossil resources in residential buildings is the trend of the energy structure progress, and also is the trend

Fig. 7. The solar air heating system (heat storage for running).

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Fig. 8. The solar air heating system (supplying hot water in summer).

of society progress and development. The BISE is a method that integrates solar technologies or devices into residential buildings on the basis of keeping original cultural features and unique appearance of buildings. From the aspects of technologies and aesthetics, BISE not only achieves the full integration of buildings and solar systems, but also realizes the harmony and unity of the overall appearance. To realize the real combination of solar heat system and architecture, BISE design is necessary. Namely, in residential building design stage, it is necessary to take solar energy system into consideration, and to make it as an essential part of residential building rather than an additional redundant component after the completion of buildings. As residential component elements, each component in solar system is reasonable arranged and they are organically integrated with roof, wall, etc. It will make the living space present brand-new molding and new image by the integration of solar energy systems appearance design and residential building design, and the esthetic feeling in buildings will be greatly enhanced. It is well known that BIPV (Building Integrated Photovoltaic) is a kind of new concept in solar power, which has been the early form of BISE. In BIPV, the system provides electricity by solar photovoltaic panels laid on the external surface of residential building envelope enclosures. BIPV has many advantages, such as saving the power grid investment, reducing the transmission losses and relieving the demand for electricity. What’s more, photovoltaic panels could replace the expensive exterior materials to perform the function of architectural decoration, so it will lead to an extensive application in solar power generation. BIPV, as a joint point of huge construction market and great potential PV market, will enjoy great potential and vast development prospects. At present, BIPV system has been widely developed in the United States, Europe and Japan [5,12,24]. According to the construction technology, BIPV can be divided into two categories: building integrated photovoltaic materials and building combined photovoltaic materials. In the first form, the solar battery is pre-installed on

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the surface of building envelope enclosures in manufacturing plant, and then it is installed on buildings with ordinary building materials on site. In addition, the material life and waterproof properties should be same with ordinary building materials. In the latter form, the solar battery components composed of toughened glasses and aluminum alloy framework have the functions of building materials, especially the good waterproof, so it could be directly used to replace building materials. To facilitate the maintenance of buildings, the life of solar battery in building combined photovoltaic materials must well match with surrounding building materials. In the long run, the mode of building combined photovoltaic materials will become the mainstream of BIPV. Building Integrated Photo-thermal (BIPT) is another part of BISE. Solar thermal energy could provide hot water, improve indoor air quality and air comfort, and generate power. At present, solar hot water supply system is the most sophisticated methods of solar energy heat utilization in China. In this system, the solar energy is converted into heat energy to meet people’s requirements in production and living. Solar ventilation is a kind of natural ventilation measures by means of hot pressing. In this system, the air temperature difference between inlet and outlet will provide buoyancy for air flow to increase indoor ventilation volume, and then the room temperature will decrease correspondingly. In solar-thermal power generation system, the heat collected by parabolic or wing mirrors is converted into electricity by heat exchange devices. Compared with BIPV, Solar-thermal power generation technology avoids the expensive silicon photoelectric conversion process, so the cost of solar power is greatly reduced. At present, although solar-thermal technology is widely used in China, the new concept of BIPT is rarely acknowledged. The method of BIPT takes into account the construction, technology and aesthetics, so the damage to building exterior and landscape by traditional solar techniques will be replaced. For using solar-thermal systems in the residential buildings, an important technical problem is to meet the basic requirement of the solar energy heat utilization. Meanwhile, the designers and engineers have to integrate building and solar systems together on the basis of the basic functions, such as waterproofing. In addition, how to realize the BIPT for residential buildings that have installed existing solar energy heat utilization system requires some consideration in order to make BIPT a part of energy saving renovation of existing buildings in China. 5. Conclusions Compared with traditional energy sources, solar energy as a kind of natural resource has incomparable advantages because of its abundant reserves and the fact that it is nonpolluting. Solar energy could play a significant role in residential building energy saving, particularly in developing countries. The BISE design is a method that integrates solar technologies or devices into residential buildings, which not only achieves the full integration of buildings and solar systems, but also realizes the harmony and unity of the overall appearance. So the BISE design could lower the

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barriers for adopting solar-power in residential buildings. China is a large country and regional resources differ from each other, so it is necessary to develop local technology to realize the wide use of BISE design in residential buildings. On the other hand, the research of energy saving technologies should be combined with practice developing applied approaches (such as BISE) to realize low cost to increase the feasibility and availability of solar-powered residential buildings. For China to become a sustainable society in terms of energy use, the application of solar technologies is a critical element of a long-term plan to promote the development of building energy efficiency. Acknowledgments This work is financially sponsored by the National Natural Science Foundation Committee of China (Subject Numbers: 51378365) and is financially supported by National "Twelfth Five-Year" Science & Technology Support Plan: the city high density space efficiency optimization key technology research (Subject Numbers: 2012BAJ15B03). References [1] Aaditya G, Pillai R, Mani M. An insight into real-time performance assessment of a building integrated photovoltaic (BIPV) installation in Bangalore (India). Energy Sustain Dev 2013;17(5):431–7. [2] Buitenhuis A, Pearce J. Open-source development of solar photovoltaic technology. Energy Sustain Dev 2012;16:379–88. [3] Cai WG, Wu Y, Zhong Y, Ren H. China building energy consumption: situation, challenges and corresponding measures. Energy Policy 2009;37(6):2054–9. [4] Chan HY, Riffat SB, Zhu J. Review of passive solar heating and cooling technologies. Renew Sustain Energy Rev 2010;14(2):781–9. [5] Cheng CL, Sanchez Jimenez CS, Lee MC. Research of BIPV optimal tilted angle, use of latitude concept for south orientated plans. Renew Energy 2009;34(6):1644–50. [6] Debije MG, Verbunt PPC. Thirty years of luminescent solar concentrator research: solar energy for the built environment. Adv Energy Mater 2012;2(1):12–35. [7] Energy Information Administration. Carbon dioxide emissions by country, 1990-2030. Carbon Dioxide emissions Charts. Available at. :, http://rainforests.mongabay.com/09-carbon_emissions.htm; 2005. [8] Gao X, Fan G, Luo C, Gu Z. A study on engineering application of solar heating system Assisted by heat Pump. International Refrigeration and Air Conditioning Conference; 2008. [9] Gao X, Feng S, Hu W, Zheng F, Wang H, Luo C, et al. Development and application of engineering-scale solar water heater system assisted by heat pump. Proceedings of ISES World Congress 2007vol. I–vol. 292 V. Springer Berlin Heidelberg; 2009. pp. 2104–7. [10] Gao XJ. The life cycle routes for the green residential buildings in China’s low-carbon city background. Adv Mater Res 2011;347: 1387–90. [11] Goli c K, Kosori c V, Furund zi c AK. General model of solar water heating system integration in residential building refurbishmentdPotential energy savings and environmental impact. Renew Sustain Energy Rev 2011;15(3):1533–44. [12] Hammond GP, Harajli HA, Jones CI, Winnett AB. Whole systems appraisal of a UK Building Integrated Photovoltaic (BIPV) system: energy, environmental, and economic evaluations. Energy Policy 2012;40:219–30. [13] He BJ, Yang L, Ye M. Building energy efficiency in China rural areas: situation, drawbacks, challenges, corresponding measures and policies. Sustain Cities Soc 2014;11:7–15.

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