| Energy consumption for heating buildings accounts for almost 20% in overall local social in areas north of China. At the same time, during heating time the CO2 emitting of local region air is also more than non- heating time. Energy use in buildings is almost up to 27.6% in whole social energy consum- ption. Although average person using energy in China is no more than half of that in the word, the gross of energy consumption has reached number two. With the economic increasing growth and a promotion in living standards, energy consumption should be certainly increased. Therefore energy use in buildings has become one of the central issues for sustainable development in China.In the recent 10 years, By means of the principle of saving energy, protecting environment, improving dwelling qualification and so on, China has made a series of building energy codes and standards, such as the first step that heating residential buildings conserve energy 30% and the second step of energy efficiency 50%. But even if the exsiting building energy standard, compared with advanced levels of that in the world, China is still far behind. To further shorten this gap and reduce energy consumption, it is indispensable to improve building energy standard.Study on building energy efficiency 65% in Xi'an region indicates that heating energy consumption of new residential building designs is reduced 65% in general building design from 1980 to 1981, that is the index of coal consumption is decreased 65%. At the same time, the change from exiting energe efficiency 50% to energy efficiency 65%, which further reduced energy consumption is whole beard by building.Being based on exsiting building energy standard, the index of heat consumption ofenergy efficiency 65% residential buildings is calculated through compared with the thermal property and the construction of envelope structure between multistorey residential buildings with R.C-brick construction in rough 1980 and recent 10 years, energy efficiency buildings and non- energy efficiency buildings in Xi'an region. Then according to index value, the heat transmission. R-value of every building envelopes is specified. And then according to the R-value, being based on Xi'an exsiting building energy standard design and exploiting Xi'an exsiting construction technology and energy conservation materials, several structure design plans of energy efficiency 65% for multi-story and R.C-brick construction residential buildings are proposed. Finally according to optimize envelop structure system design, its cost-benefit analyses is evaluated.Through the study on multi-story and R.C-brick construction residential buildings in Xi'an region, it is conclued that adopts new energy structure system and is based on building energy efficiency 50%, using Xi'an exsiting thermal insulation materials and energy -saving products, proper increasing the thickness of thermal insulation layer and substituting single-glazed windows for double- glazed windows, which is feasible in technology; Increased expensive for Energy efficiency 50% residential buildings accounts for approximately 15% in whole project cost, which is also feasible in economy. Xi'an locates in region of Earthquake Design Intensity, 8°C, therefore there is a significant effect about thermal bridge because of exsiting many construction columns. A external additional insulation walls should be first selected. The energy efficiency design of external walls in residential building must simultaneously take into account the type, the shape of building and the type of its windows. Adopting energy-saving windows can efficiently lighten the burden of additional insulation of external wall. At the same time it can simplify the construction measure, cut down investment and benefit to extend application for new type wall.
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