Study on indoor thermal conditions of a triple envelope incorporated with PCM in the passive solar building under different climates by analytical method

Clarifying the thermal mechanism of buildings provides a basis for the scientific design and optimization of envelopes. This study explored the mechanism of outdoor thermal disturbances, thermal storage materials, the building noumenon and internal heat sources (IHS) affecting indoor thermal conditions (ITC) by analytical method. The triple envelope incorporated with phase change material (EIPCM) form of “outer insulation layer + structural layer + inner PCM layer” was determined and theoretically derived a predictive model of the indoor thermal conditions (PMITC) to evaluate thermal comfort in five representative regions of northwest China. Following that analyzed the significance of the influencing factors on ITC employing linear regression. The results illustrated that ITC was mainly affected by the coupling of four aspects factors. More in detail, solar radiation entering the room exploited the most prominent effect on the increase in average indoor temperature. PCM layer only affected the temperature amplitude but not the average indoor temperature. The sensible heat storage of the structural layer had a weaker effect on ITC than the PCM layer. The lowest temperatures in Yinchuan and Xi’an were both above 16 °C, while Urumqi had a higher temperature fluctuation of 2.1  °C and an average indoor temperature of 6.32 °C lower than Xi’an. Based on the estimate of ITC and degree hours (DH), the application effects of PCM in buildings in five regions can be summarized as complete thermal comfort (Yinchuan and Xi’an), partial thermal comfort (Lanzhou and Xining) and complete thermal discomfort (Urumqi). For the different factors that affected ITC, the window-to-wall ratio (WWR) had the highest coefficient of determination exceeding 93 % and the building dimension performed the lowest around 26 %.