Research On Nearly-zero Energy Retrofit Methods For Residential Buildings In Severe Cold Regions

In recent years,how to effectively reduce energy consumption and carbon emissions has been a hot research topic in the construction industry,and nearly-zero energy buildings have been widely studied for their advantages in energy saving and environmental protection.And because the total area of urban buildings in China increases by more than 1 billion m² every year.Therefore,this paper proposes a scheme to transform existing buildings into nZEB to achieve lower energy consumption and reduce carbon emissions in the building industry.In this paper,a residential building in Changchun City,Jilin Province,Northeast China is taken as the research object,and the building is started to be retrofitted and studied according to the relevant energy consumption limits in the Technical Standards for nearly-Zero Energy Buildings promulgated by China,and the changes in building energy consumption during the retrofitting process are analyzed.First,the building energy consumption simulation was performed using building energy simulation and analysis software,and then the reliability of the building model was verified according to the method proposed in ASHRAE Guide 14-2014.The validated model can be used to evaluate the subsequent energy consumption of different building retrofitting options.Using the integrated value of building energy consumption as the main evaluation index,four passive parameters,namely,heat transfer coefficient of exterior walls,number of air changes N₅₀,heat transfer coefficient of windows and heat transfer coefficient of roof,were varied,and the effects of different passive building factors on the integrated value of building energy consumption were evaluated by using orthogonal test with extreme difference analysis and analysis of variance.The effects of the four passive building factors on TECI were obtained in descending order as follows:exterior wall heat transfer coefficient>number of air changes N₅₀>window heat transfer coefficient>roof heat transfer coefficient.The data analysis led to the best solution for further building retrofitting,concluding that by simply reducing the heat transfer coefficient of exterior walls from 0.5 to 0.2 W/（m²·K）and the number of air changes N₅₀ from 3.6 to 0.4 ac/h,while keeping the roof heat transfer coefficient and window heat transfer coefficient constant at 0.4 and 2 W/（m²·K）,respectively,the TECI can be reduced by45.31%to meet below the standard value of 55k Wh/（m²·a）specified by the nZEB standard.In addition,this paper clarifies the way of supplying electricity in China in the future period by comparing the primary energy generation capacity and its share between G7 countries and China.The carbon dioxide emissions of heat pump heating,coal-fired boiler heating and cogeneration heating are compared and analyzed by using the carbon dioxide emission factor of grid power supply and the carbon emission factor of coal.Since the carbon emissions of air source heat pump systems are mainly from the carbon emissions of electricity supply,the carbon emissions generated are higher compared with those of combined heat and power.Therefore,for northeast China,combined heat and power is still the main heating method,but with the decarbonization of the power system and the improvement of the COP value of heat pump units,coal-fired boilers will be replaced by clean heat pumps.The adoption of central heating will not be abandoned until the carbon emissions of our electricity supply are significantly reduced.The above conclusions can provide a reference for the actual buildings to carry out nZEB retrofit projects.