Research On The Influence Of Thermal Bridges On Energy Consumption Of Low-Rise Buildings In Hot-Summer And Cold-Winter Zone

The energy consumption of building is affected by the thermal bridges.Studying the effects of thermal bridges on building energy consumption in hot-summer and cold-winter zone promotes the implementation of the "Energy-saving Design Standards for Energy-efficient Buildings in Residential Buildings in Hot-Summer and Cold-Winter zone".It is also of great significance to achieve the relevant goals "in the 13th Five-Year Plan for Building Energy Efficiency and Green Development".This paper used the equivalent heat transfer coefficient method and the WUFI Plus heat-humidity coupling analysis method to calculate the overall building energy consumption with and without thermal bridges.Considering the influence of factors such as soil temperature,radiant heat transfer,and heat-moisture coupling effects,the influence of thermal bridges on overall building energy consumption was analyzed.Firstly,a two-dimensional steady-state thermal bridge heat transfer model was established by THERM.The influence of soil temperature and radiant heat transfer on energy consumption was considered by the energy consumption of thermal bridge.Based on the finite element method,the temperature distribution and heat flux density of the wall were obtained,and the heat transfer coefficient value of the wall was reached based on this.The effect of soil temperature and radiative heat transfer on the average heat transfer coefficient was further studied by the control variable method.According to the equivalent heat transfer coefficient method,this heat transfer coefficient was used as the average heat transfer coefficient of the wall substituted into DesignBuilder to calculate cooling and heating loads on the design day and total annual energy consumption.the influence of the thermal bridge on the building load and energy consumption under the equivalent heat transfer coefficient method was arriveded at by comparing the above calculation results with the building load and energy consumption results without considering the thermal bridge.The influence of thermal bridges on the energy consumption of low-rise buildings in a two-storey residential building was analyzed,which was separately located in Nanchang,Chengdu,Wuhan and Shanghai.The simulation results showed that:when the equivalent heat transfer coefficient method was used,the calculated results of THERM and DesignBuilder increased by 27.02%?30.28%,and the annual energy consumption risen by 1.62%?3.04%.The average heat transfer coefficient of the wall during the cooling period increased by 27.02%?30.28%,the cooling load driven up by 3.36%?4.63%,and the energy consumption increased by 0.09%?1.08%.The average heat transfer coefficient of the wall during the heating period grown by 20.81%?25.00%,the heat load increased by 6.49%?7.76%,and the energy consumption raised by 3.56%?5.99%.In the same season and city,the change of DesignBuilder building load was positively correlated with the change of the average heat transfer coefficient of the wall.Under the same variation,the effect of soil temperature on the average heat transfer coefficient was greater than the outdoor air temperature.Secondly,in order to analyze the influence of thermal bridge and overall building energy consumption when considering the thermal-moisture coupling effect,WUFI Plus was used by this paper to analyze the influence of thermal bridge on the annual energy consumption of the whole building under the equivalent heat transfer coefficient method.An overall building heat and humidity test platform was set up to verify the accuracy of WUFI Plus simulation,and the experimental values were compared with the simulated values of WUFI Plus.The results showed that the simulated values agreed well with the experimental values,and the absolute error of the temperature parameters was within 2 degrees.The relative error of the relative humidity parameter was within 5%,The simulation results showed that when the thermal bridge was not considered,the entire building's the annual energy consumption of WUFI Plus was 1.15%?2.2%higher than DesignBuilder.The energy consumption raised by 1.30%to 2.06%and the energy consumption during the heating period increased by 1.00%to 2.82%during the cooling period.When calculating the thermal bridge energy consumption by the equivalent heat transfer coefficient method,the entire building's the annual energy consumption of WUFI Plus was increased by about 2.75%to 3.81%compared to DesignBuilder,of which the energy consumption during the cooling period driven up by 2.88%to 3.84%,and the energy consumption during the heating period risen by 2.63%?3.67%.Finally,a three-dimensional heat bridge heat transfer model was established by WUFI Plus to calculate the annual energy consumption of the entire building.The results were compared with the results of building energy consumption without considering the thermal bridge and the equivalent heat transfer coefficient method.The simulation results showed that the annual energy consumption of the overall building calculated by the three-dimensional thermal bridge model increased by 24.50%to 28.14%compared with that without the thermal bridge,among which the energy consumption during the cooling period risen by 19.67%to 22.10%,and the energy consumption during the heating period raised by 29.46%to 32.57%.Using the equivalent heat transfer coefficient method,the annual energy consumption increased by about 3.23%to 4.29%compared without a thermal bridge,in which the cooling period increased by 2.01%to 2.40%,and the heating period risen by 5.45%to 6.10%.Using the three-dimensional thermal bridge model,the annual energy consumption of the entire building increased by approximately 20.56%?23.02%over the equivalent heat transfer coefficient method.The cooling period raised by 17.31%?20.89%,and the heating period increased by 22.26?29.94%.The calculation accuracy of the thermal energy consumption of the three-dimensional thermal bridge was much higher than the equivalent heat transfer coefficient method.Because the difference between the indoor and outdoor temperature during the cooling period was smaller than the heating period,the annual energy consumption change during the cooling period was smaller than the heating period.