Heat transfer model of hot-wall Kang based on the non-uniform Kang surface temperature in Chinese rural residences

Chinese Kangs are widely used for home space heating in rural residences. However, the energy efficiency of a traditional Kang is less than 20%. Thus, the hot-wall Kang is gradually becoming popular in Jilin, Heilongjiang and Inner Mongolia of China because of its higher energy efficiency, comfortable indoor thermal environment and flexibility of application. The hot-wall Kang has three operation modes. The heat transfer model of Kang in previous studies was developed based on the three assumptions, which include the uniform Kang surface temperature, the neglect of the radiation effect of gas and the thermal storage of ash soil layer. However, the model of hot-wall Kang in this paper was improved with respect to the three assumptions, which were discussed in this paper. Then, the model was validated by experiments and applied to optimize the thermal performance of the hot-wall Kang. The results showed that the simulation results were in good agreement with the measurement results. Furthermore, based on the verified model, the better thickness and material of the cover board were found to be 0.06 m and foam concrete, respectively.