Impacts Of Indoor And Outdoor Air Temperature On Net Solar Heat Gain Of Building Walls In Winter

With the rapid development of economy in the middle and lower reaches of the Yangtze River in China,space heating has attracted more and more attentions in current days because of the cold and moist climate as well as the poor thermal comfort in this region,which would result in a considerable increase of the total energy consumption of buildings.One of the main factors influencing the heating energy consumption is the effective absorption rate of solar radiation of building envelopes.Therefore,to accurate estimation of the practical solar absorption rate on the south wall is very important to explore the stretagies of reducing the building heating energy consumption.The exterior walls of buildings in the northern region ususally use the external layer for thermal insulation,while in the hot summer and cold winter zone,the temperature difference between the indoor and outdoor air is far less than that in the northern region in winter,so both the internal and external thermal insulation are very popular.Under the same solar radiation intensity,the heat capacity of the exterior wall's outer surface is different,so the temperatures and the convection heat dissipations of the exterior wall's outer surface will also be different,thus results in a significant impact on the practical absorption of the solar radiation by the south walls.The existing studies show that the thermal properties of the surface layer of the south wall exposed to the outdoor environment(insulation layer or bearing layer)would affect the absorption of solar radiation on the walls.However,these studies focused on the steady periodic climate condition or a typical day weather condition.In practice,the buildings are irradiated in the consecutive-sunny-days,the temperature of building outer surface may be gradually increased but the absorption of the solar radiation on the exterior wall may be reduced.Therefore,the number of consecutive-sunny-days has a certain impact on the practical absorption of solar radiation on the building envelopes,which cannot be neglected in the hot summer and cold winter region where the heating energy consumption is sensitive to the absorption rate of the solar radiation.The dynamic heat transfer process of the south wall with solar radiation in the consecutive-sunny days is simulated by using the numerical simulation method.The relationship between the solar heat gain of the building south walls,the indoor and outdoor air temperature,the location of insulation layer,as well as the consecutive-sunny-days are then analyzed.The results show that under the same indoor air temperature,when the outside temperature is increased by 4 °C,the outer surface temperature of the sourth wall is also increased by about 4 °C regardless of the inner or outer insulation,and the net heat gain of the south wall is increased by about 220 k J/m~2.For a fixed outside air temperature,when the indoor air temperature is increased by 5 °C,the outer surface temperature of the sourth wall regardless of the inner or outer insulation is increased a slight,which result in the net solar heat gain of the south wall being decreased by about 280 k J/m~2.With the same outdoor air temperature,when the number of consecutive-sunny-days is within 3 days,the net solar heat of the south wall with internal insulation is 30 % to 80 % higher than that with external insulation,so the wall with inner insulation is more benificial for the absorption and then for the solar energy usage.While the net solar heat gain of the south wall with internal insulation is approximately equal to that with external insulation in the long consecutive-sunny-days(e.g.,more than 10 days).In addition,a correlation between the daily real absorption rate of solar radiation on the south wall and the averaged indoor-outdoor temperature difference,as well as the number of consecutive-sunny-days,is developed by using the mathematical fitting method,which can be used as a method for calculating or estimating the actual solar heat gain on the south wall under the condition of different indoor and outdoor temperature differences and insulation locations.