Optimizing environmental insulation thickness of buildings with CHP-based district heating system based on amount of energy and energy grade

The increase of insulation thickness（IT）results in the decrease of the heat demand and heat medium temperature.A mathematical model on the optimum environmental insulation thickness（OEIT） for minimizing the annual total environmental impact was established based on the amount of energy and energy grade reduction.Besides,a case study was conducted based on a residential community with a combined heat and power（CHP）-based district heating system（DHS） in Tianjin,China.Moreover,the effect of IT on heat demand,heat medium temperature,exhaust heat,extracted heat,coal consumption,carbon dioxide（CO2） emissions and sulfur dioxide（SO2） emissions as well as the effect of three types of insulation materials（i.e.,expanded polystyrene,rock wool and glass wool） on the OEIT and minimum annual total environmental impact were studied.The results reveal that the optimization model can be used to determine the OEIT.When the OEIT of expanded polystyrene,rock wool and glass wool is used,the annual total environmental impact can be reduced by 84.563%,83.211%,and 86.104%,respectively.It can be found that glass wool is more beneficial to the environment compared with expanded polystyrene and rock wool.