Study On Optimizing Thermal Insulation Thickness Of Building Envelope For Energy-saving Renovation Of Existing Residential Buildings In Cold Areas

Increasing insulation layer is the main measure of energy-saving renovation of existing residential building envelope structure in cold area.How to determine the thickness of insulation layer has an important impact on the cost and energy-saving effect of renovation.Using ANSYS and P₁-P₂ economic models,energy consumption calculation and insulation layer thickness optimization models for exterior walls with different orientations considering the influence of thermal bridge are established,and roof energy consumption calculation and insulation layer thickness optimization models considering the influence of solar radiation and long wave radiation are established.Based on the uniform design method and the economic model of DesignBuilder and P₁-P₂,the energy consumption calculation and the globle optimization model the influence of heat transfer,solar radiation and long wave radiation for the envelope structure are established.The economic thickness of two kinds of insulation materials under different heating sources is calculated by the globle optimization model and the local optimization model of the insulation of the envelope structure and the results are compared.The main conclusions are as follows:（1）The optimization model of thermal insulation thickness of exterior wall considering the influence of thermal bridge is established,and the economic thickness of EPS plate and XPS plate is calculated.It is found that orientation has little effect on the economic thickness of insulation layer,but has a great influence on net present value（NPV）and investment payback period.In the reform of exterior wall energy saving,the influence of energy consumption towards exterior wall should be fully considered.（2）The optimization model of roof insulation thickness considering the influence of solar radiation and long wave radiation is established.The economic thickness of XPS and PUR plates is calculated for different roofs.Comparing with the economic thickness of the insulation layer without considering the radiation effect and ignoring the long-wave radiation only,it is found that the solar radiation and the long-wave radiation have great influence on the optimization results of the thickness of the insulation layer.In the optimization process,the influence of the solar radiation and the long-wave radiation on the energy consumption of the roof should be considered comprehensively.（3）The globle optimization model of thermal insulation thickness of enclosure structure considering the influence of thermal bridge and solar radiation is established,and the economic thickness of thermal insulation thickness of enclosure structure is calculated.The energy-saving rate of buildings after transformation is analyzed.When coal is used as heating heat source,the energy-saving target of buildings should be set at57%,and when natural gas is used as heating heat source,the energy-saving target of buildings should be set at 62%.（4）Comparing the results of energy consumption calculation by equivalent heating degree time method and unsteady state method,the calculation method of energy consumption has a greater impact on the net present value and investment recovery period of economic thermal insulation thickness in local optimization,while the calculation method of energy consumption has a greater impact on the calculation of thickness,net present value and investment recovery period of economic thermal insulation layer in overall optimization.The unsteady calculation method should be selected to calculate the energy consumption of the enclosure structure when establishing the optimization model of the thickness of the insulation layer of the enclosure structure.（5）The net present value of the economic insulation thickness of the latter increased by 2%on average.When determining the economic insulation layer thickness of the envelop structure,the mutual influence of the thermal performance of the external wall and roof should be comprehensively considered for the overall optimization.