Study On Thermal Performance Diagnosis Method Of Existing Building Envelopes

With the continuous development of society and urbanization,China’s construction scale is also expanding.A large number of completed buildings every year make the stock of China’s construction area grow rapidly.But the following is a huge building energy consumption which has become an important problem restricting the development of our country.At present,there are many non-energy-saving buildings in our country.Energy-saving retrofits of existing buildings will be an imperative because of the significant economi c and social benefits.The building envelope has a great influence on air-conditioning energy consumption and indoor thermal comfort environment.To retrofit the building envelope,it is necessary to diagnose it first,so as to determine whether it has ene rgy saving potential and whether it needs retrofits.If it is decided that the building needs to be retrofitted,a further judgment will need to be made as to which envelope is to be retrofitted.Most of the existing diagnostic methods for the thermal perf ormance of building envelopes need complex field tests,which is inconvenient in field operation.Based on the above background and problems,this paper proposes a convenient thermal performance diagnosis method for existing building envelopes.By this method,the three thermal parameters,heat transfer coefficient,decrement factor and time lag,can be obtained through corresponding mathematical processing after fie ld testing the indoor and outdoor temperature sequences and the geometric size of building envelopes.After the diagnosis,the input-output ratio of the retrofit can be obtained by calculating the energy-saving rate,and then the optimal retrofit scheme can be determined.The main research contents of this paper are: 1)A convenient diagnostic method for heat transfer coefficient of the envelope was presented.This method requires only on-site testing of indoor and outdoor temperature sequences and the geometric dimensions of the envelope.The corresponding model building was established in the De ST software,and the thickness of the envelope of the model building was changed to change its heat transfer coefficient.When the energy consumption of the model building was closest to that of the prototype building,the heat transfer coefficient of the model building was the comprehensive equivalent heat transfer coefficient of the building to be diagnosed.Through orthogonal tests and regression analyses,the heat transfer coefficient of each type of envelopes can be further obtained.2)Even in the case of the same heat transfer coefficient,the difference in the heat storage and heat release characteristics of building envelopes will result in different air conditioning loads and different indoor thermal environments.Taking this into account,on the basis of the completion of the heat transfer coefficient diagnosis,this paper selected the decrement factor and time lag in the thermal inertia index and proposed a method for diagnosing decrement factor and time lag of building envelopes.This method does not need additional field tests.By orthogonal test and regression analysis,the value combination of the decrement factor and time lag of envelopes was obtained when the actual heat sequence of envelopes was closest to the theoretical heat sequence.3)In order to illustrate the application process of the method and to prove the accuracy of the proposed method,an experimental house located in Changsha was taken as an example to calculate.According to the given diagnostic steps,the heat transfer coefficient,decrement factor and time delay of the experimental house were obtained.Comparing the diagnosis results with the real parameters of the small room,the two groups of values agreed well,which proved the feasibility and accuracy of the proposed method.In conclusion,the diagnostic method proposed in this pap er has the advantages of convenient operation in field tests and can simultaneously take into account the three thermal parameters of envelopes,namely heat transfer coefficient,decrement factor and time lag.