| In recent years,with the continuous expansion of the application scale of the central heating system in our country,and a considerable proportion of the old heating pipe network is out of service,the possibility of accidents in the heating system is growing.When a large-scale heating system accident occurs,stopping heating or insufficient heating will cause the indoor temperature of the building to drop,affect the quality of life of the thermal users,and even cause serious economic losses and social consequences.The performance of building thermal reserve is the ability of using building heat capacity to resist indoor temperature drop under heating accident condition.The research on how to improve the performance of building thermal reserve and its impact on the reliability index of heating system is the key link and new idea to explore the improvement of heating system reliability from the heating demand side.In this study,theoretical analysis,field measurement and numerical simulation are used to carry out the research work.The main research contents include: to test and verify the semi theoretical and semi empirical calculation formula of the indoor temperature of buildings under heating accident conditions,to put forward the modified calculation formula suitable for the prediction of the indoor temperature of buildings under accident conditions in the heating planning stage,to use the numerical test to verify the accuracy,to determine the sensitivity sequence of the key factors affecting the performance of building thermal reserve,and to put forward effective technical measures for improvement The value ranges of limited heating coefficient,limit of accident repair time and optimal building thermal reserve coefficient in different climate zones are established.The main contributions of this study include:(1)A general calculation method is established for several key complex parameters in the semi theoretical and semi empirical calculation formula of building room temperature under heating accident condition established by foreign scholars.It includes the calculation formula of unit temperature difference heat loss for the calculation of total heat loss of buildings,the calculation method of total heat capacity of buildings and the calculation program,and the calculation method of heat capacity of new convection and radiation types of heat dissipation equipment for the current lack of heat capacity of heat dissipation equipment.(2)The calculation formula of building room temperature under the accident condition of heating is verified by actual measurement,and the modified calculation formula suitable for predicting the building room temperature under the accident condition of different climate zones in the heating planning stage is proposed.First of all,the accuracy of the calculation formula of building room temperature under the condition of stopping heating is verified by the actual measurement of three types of cooling equipment in cold zone A.then,in view of the unpredictability of outdoor temperature parameters in the calculation formula in case of an accident,five correction methods are proposed for comparative analysis,and it is found that the relative deviation of the formula is the smallest when the average temperature of the coldest month is used to replace the outdoor temperature in case of heating accident;Finally,In order to overcome the limitation of actual measurement and verification,a numerical model of building cooling process under heating accident condition is established based on COMSOL Multiphysics.Under the conditions of severe cold zone A,B,C and cold zone A,B,the numerical tests of radiator stop heating condition and limited heating condition are carried out,and the accuracy of the room temperature correction formula under heating accident condition is verified.The new function of the modified formula can be used to predict the room temperature drop of buildings in different climate zones.(3)The sensitivity ranking of the key factors affecting the thermal storage performance of buildings is determined,and the effective technical measures to improve the thermal storage performance of buildings are proposed.Based on the established numerical model of building cooling process under heating accident conditions,the thermal performance of different buildings is constructed.Through simulation analysis,the sensitivity order of influencing factors of building cooling under heating accident conditions is as follows: unit temperature difference heat loss > heat capacity of cooling equipment > outdoor air temperature > heat capacity of peripheral protective structure.Furthermore,it puts forward the technical measures to reduce the unit temperature difference heat loss of the room and to increase the heat capacity of the room.(4)The rules of limit heating coefficient and accident repair time in different climate zones are improved.According to the existing different levels of building energy conservation,through simulation calculation,the current range of building thermal reserve coefficient in China is 50-90 h.Under this condition,the value range of limited heat supply coefficient is:0.51<?<0.71 in severe cold area,0.31<?<0.58 in cold area;the best building thermal reserve coefficient in severe cold area is 80-90 h,and the corresponding time limit of heating accident repair can be set as 58 h,the best building thermal reserve coefficient in cold area is 70-90 h,and the corresponding time limit of heating accident repair can be set as 56 h.The research results are more detailed than the limit repair time of 54 h in the current code.It has important theoretical value and application value for establishing and improving the index of building thermal reserve coefficient,setting reasonable heat supply accident limit heat supply coefficient and allowable repair time. |
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