Research On Green Assesment System For Public Buildings In Hunan Area Based On Thermodynamic Method

Energy use, environmental protection and the preservation of natural resou rces have received more and more attention with the popularity of sustainable development. Buildings consume a lot of energy and resources as being an essential part of human life. In building energy consumption, public building energy consumption problem is particularly prominent, so to achieve energy conservation and emissions reduction of public building have become the key point of sustainable development of the society.Based on the theory of total life cycle and thermodynamic analysis, energy consumption, exergy consumption, carbon dioxide emissions and construction costs of different phase( building materials production phase, construction phase, running phase, maintenance phase and demolition phase) in public building life cycle have been discussed in this paper first. Then five cases of public buildings in Hunan province are analyzed. The research result shows that the energy consumption, exergy consumption, carbon dioxide emissions and construction costs per unit area of commercial buildings are si gnificantly higher than office buildings’. In building life cycle, the energy consumption of materials production phase and running phase account for absolute proportion. And the total energy consumption of the building is higher when the proportion of materials production energy consumption is lower and running energy consumption is higher. Therefor, to reduce energy consumption effectively, we should analyze the energy use in total life cycle and distribute energy reasonably.Secondly, the linear equation, quadratic equation and Gauss equation between energy consumption and exergy consumption and exergy-energy ratio are established based on the exergy-energy ratio concept. Then the critical exergy-energy ratio is proposed which can be a new thermodynamic index for green building evaluation. The research result indicates that there is a lower limit exergy-energy ratio of 0.7616 in the the linear equation model, and there is a maximum exergy-energy ratio of 0.7850 in the quadratic equation model, and in the Gauss equation model, the exergy-energy ratio approaches 1.000 when the energy consumption approaches 6100 MJ/m2, and the curve flats when energy consumption is between 15000 ~29000MJ/m2.Finally, based on Analytic hierarchy process and exergy-energy ratio evaluation, the green evaluation of the five building cases in Hunan province are analyzed as the energy consumption, exergy consumption, carbon dioxide emissions and construction costs to be the indicators. The result indicates that the green weight of co mmercial buildings are lower than office buildings, and the exergy-energy ratio of the building which the green weight is highest is neither the highest nor the lowest. The higher exergy-energy ratio means the higher consumption degree of high quality ener gy, thus leading to higher carbon dioxide emissions and construction costs. The lower exergy-energy ratio means that there is energy loss in the consumption process. So, to improve the green weight of building, we should find the optimum exergy-energy ratio neither the highest one nor the lowest one. The exergy-energy ratio can evaluate the utilization degree of high quality energy. We can make better green building evaluation when this thermodynamic index is applied to green building evaluation system. The improved evaluation system will provide reference to energy distribution and sustainable design of public buildings.