Optimizing Insulation Thickness Of Walls Of Buildings Based On Amount Of Energy And Energy Grade

From the perspective of reducing amount of energy and energy grade,the optimum insulation thickness of walls of buildings based on combined heat and power(CHP)-based district heating systems was studied.The innovation of this study is that a new method of optimizing insulation thickness based on amount of energy and energy grade is proposed.This method combines exhaust heat recovery of CHP plants with insulation retrofit.The change in supply and return temperature of district heating systems is the key to it.The increase of insulation thickness of walls results in the decrease of heat losses of buildings,supply and return temperature of district heating systems.The reduction of supply and return temperature creates conditions for exhaust heat recovery in CHP plants.According to the change of water temperature,the precondition of exhaust heat recovery by absorption heat pump in CHP plants was analyzed.Then,the outlet temperature from absorption heat pump,extracted heat and exhaust heat were calculated.The optimization models for determining the energetic,economic and environmental insulation thickness were established,respectively.Genetic algorithm was used to solve the above optimization models by Matlab software.In order to verify the correctness and feasibility of above optimization methods,a case study was conducted based on a residential community with CHP-based district heating systems in Taiyuan City,Shanxi Province.Finally,the optimization results of three insulation materials(i.e.,EPS,Rock wool and Glass wool)were compared and analyzed.The main results are as follows: With the increase of insulation thickness,total exhaust heat increases,and then decreases.The total extracted heat decreases gradually with the increase of insulation thickness.Take EPS as an example,it can be found that the optimum energetic insulation thickness is 0.22 m.The optimum economic insulation thickness is 0.072 m,and the optimum environmental insulation thickness is 1.381 m.Among three different insulation materials,glass wool has the best energy-saving,economic and environmental performance.No matter what kind of insulation materials,the optimum environmental insulation thickness is the largest,followed by the optimum energetic insulation thickness,and then the optimum economic insulation thickness.For different insulation materials,the effect of weight coefficient on the optimization results is consistent.No matter how the weight coefficient changes,optimum insulation thicknesses based on amount of energy and energy grade are smaller than that without considering energy grade(i.e.,without recycling exhaust heat),and the energetic reduction rate,economic saving rate and environmental emission reduction rate are higher than that without considering energy grade.This shows that when insulation retrofit is combined with exhaust heat recovery,the effect of energy saving and emission reduction is remarkable.