تجزیه و تحلیل اقتصادی اقدامات اصلاحی صرفه جویی در انرژی برای ساختمان های مسکونی شهری موجود در چین بر اساس شبیه سازی حرارتی و بررسی سایت

Energy-saving renovations of existing residential buildings have proven to be very helpful in alleviating the pressure of energy shortages and CO2 emission, but an economic analysis of the measures by using a life cycle cost (LCC) method is very important and necessary to determine whether to implement them or not. Based on thermal simulation and site investigation, the paper uses one urban existing residential building in Hangzhou city of China as the subject building, and analyzes the economic benefits from the energy-saving renovation measures through the LCC method. The findings clearly show that the investigation of the factual electricity consumption of the subject building is very important to predict accurately the energy-saving effects and financial benefits of the measures for the building, because of the great discrepancy between in fact and in thermal simulation of the heating and cool loads, and the too cheap electricity price may hamper the development of energy-saving implementations in residential sector in China.

Both the abroad environmental and the domestic energy crisis pressures had made energy savings one of basic national policies in the 11th Five-year Economic Growth Plan of China. Along with the rapid economic development, urbanization and improvement of people's living conditions in the past decade, residential energy consumption has risen sharply in Hangzhou city of China. Hangzhou Statistical Yearbook (2007) shows that the total urban residential electricity consumption in Hangzhou city increased by 93.75% while the population growth was only 9.22% from 2001 to 2006. In contrast, energy shortage in the city had been restricting the economic development seriously. To make matters worse, almost all existing residential buildings in the city were built with poor thermal quality. Such statistics clearly reveal that renovation (upgrading the condition) with energy-saving measures that can improve the energy performance of those buildings will be highly valuable to alleviate the pressures of energy shortages and CO2 emissions of the city. However, the initial investments make the decision-makers think twice about applying energy-saving measures to renovate those buildings. In fact, the economic benefits of the measures from the life cycle assessment (LCA) viewpoint may be the most critical factor in the energy-saving renovations. A number of studies had addressed the issue. Kohler (1999) thought that the renovation (upgrading the condition) of existing buildings should be a priority as it offered an opportunity to take cost-effective measures to transform the residential structures into resource-efficient and environmentally sound buildings. Equally important was the fact that renovation costs were significantly lower than demolition and reconstruction. Gustafsson (2000) used life cycle cost (LCC) to optimize the retrofit measures and minimize the cost of them for renovating the existing residential buildings in Sweden. Papadopoulos et al. (2002) concluded that the issue of energy renovation measures in the existing buildings of Greece was important and complex, and the energy potential was significant. Verbeeck and Hens (2005) proved the insulation of the envelope of the existing buildings in Belgium as the most effective and durable measures, also economically feasible depending on the available retrofit budget and the underlying motivation (limited investment, economic benefit at long term). Arslan and Kose (2006) showed the cost-effectiveness when optimum insulation in renovating the existing buildings in Kutahya city of Turkey was applied, moreover, energy consumption and air pollutants decreased. Tommerup and Svendsen (2006) illustrated how a profitable 80% savings potential of energy used for space heating could be identified over 45 years within the Danish residential building stock if the energy performances were upgraded through proper renovation. Lollini et al. (2006) demonstrated that significant economic advantages resulted from high-performance building envelope if the life cycle of the building was taken into account. Although the total energy consumption of China is the second in the world, the per capita or per square meter residential energy consumption is much less than that of the developed countries for different lifestyles or customs, residential policies (Long, 2007). And the energy price system in China is also different from that of developed countries, so the experience or results for those countries cannot be applied directly and simply in China, but LCC is an effective method to take the economic analysis of such an issue. Some preliminary studies available in China also proved the advantages of energy-saving renovation for the existing buildings, but only through thermal simulation or, in theory; their results should be checked further. Zhao and Lin (2005) demonstrated that the energy and economic efficiency of residential flats could be achieved with the application of appropriate energy-efficiency designs. Liu and Li (2005) showed that the increase of initial investment of the external wall insulation was acceptable and the energy effect was quite obvious. Hao and Yang (2007) showed that the initial investment (cost) would be paid back during the operational phase through less electricity consumption for energy-saving renovation of the existing residential buildings in Shanghai city. Zhao et al. (2007) analyzed the technology of energy-saving reform of existing residential buildings, and compared the energy consumptions calculated from thermal simulation by the Chinese Doe version software (CHEC), before and after the energy-saving reform. The outputs of those studies may be exaggerated and not convincing enough, for not further being analyzed by combining with the factual electricity consumption of the existing residential buildings. Some researchers in China were aware of the importance of the factual electricity consumption of residential buildings to the energy-saving study. But it is very regretful that most of the prior researchers just wanted to make clear the status quo on electricity consumption and that for cooling load and/or heating load of residential buildings through investigation. Zhong and Long (2003) investigated the cooling load of the residential buildings in Shanghai city by a survey undertaken in July 2002, and found the value was 7.94 kWh/(m2 year) in summer. Ren et al. (2003) investigated the cooling load of urban residential buildings in summer in Guangzhou city from 1997 to 1999, and found the value was 7.9 kWh/(m2 year). Hu et al. (2004) investigated the electricity consumption and cooling load of urban and rural buildings in Hubei province, and found the values were, respectively, 9.0–36.9 and 1.0–9.8 kWh/(m2 year). Wu (2005) investigated the electricity consumption of residential buildings in Hangzhou city from 2001 to 2004 and calculated the total heating and cooling loads to be 11.10 kWh/(m2 year), about one-third of the total electricity consumption of residential buildings. Only Lam (1998) applied the monthly electricity consumption to analyze the climatic and economic influence on residential energy consumption. This study will analyze the economic benefits from the energy-saving renovations of the existing residential buildings in Hangzhou city of China through the simplified LCC method, based on the energy-saving effects of the measures calculated by thermal simulation and further revised by the factual electricity consumption of residential buildings.

The study has demonstrated that a significant reduction potential of energy savings can be made from high-performance building envelopes of the existing residential buildings in Hangzhou city, but the corresponding financial and regulatory problems are to be overcome: (1) Since the renovation of existing old residential buildings is unavoidable now and in the near future, it is prudent to take into account the renovation and energy savings as a whole in order to increase the attractiveness and positive consequences of energy-saving renovations. As such, there is expected to be a shift in emphasis from improving the energy efficiency of new residential buildings towards the renovation and maintenance of existing ones. (2) A great potential for energy savings exists in Chinese residential buildings due to the fact that many structures were constructed before 2001 when the first important demands regarding the energy performance of buildings were introduced. (3) From the site investigation, the total electricity consumption of the subject building is 89,932.3 kWh/year, of which the heating and cooling loads are, respectively, 13740 and 16872 kWh/year. The total heating and cooling loads are 12.28 kWh/(m2 year). In total, it is 33.94% of the total electricity consumption. The heating and cooling loads of the subject building in fact are far less than those in thermal simulation. (4) The cooling load is more than the heating load of residential buildings in fact in the hot summer and cold winter region, so the effect of reducing the cooling load should be taken more seriously than that of reducing the heating load, if evaluating the performance of energy-saving measures. So reducing the SC of exterior windows in summer is very important, together with upgrading the insulation performance of the existing buildings’ envelope. (5) The energy-saving effects and financial benefits of the measures are quite exaggerated for the great discrepancy of the heating and cooling loads between in fact and in thermal simulation. So it is necessary to take site investigation to make clear the factual heating and cooling loads of the subject building, and revise the simulative outputs by applying them. And the site investigation of the factual electricity consumption of the subject building is very important to predict accurately the effects of the energy-saving measures for it. (6) From an economic view point, it is very disappointing that the effects of cost reduction of all measures are negative after revision, including the suitable plan. The very cheap electricity price hampers the development of energy-saving implementations in the residential sector in China, and the governments should provide certain subsidy for the energy-saving renovations of existing residential buildings, and increase the electricity price gradually.