Experimental and simulation study on the thermal performance of a novel flue composite wall

The traditional Chinese kang is widely used in rural areas of northern China for space heating in winter. However, recently, the development and application of the Chinese kang system begin to decline due to its low efficiency and poor thermal performance. A flue composite wall (FCW) is proposed in this paper to improve the energy efficiency by recovering the waste heat form the exhaust smoke discharged from the kang body. Moreover, the FCW works together with the kang system to improve the indoor thermal environment, as a supplementary heating facility. To investigate the performance of the FCW, experimental test and numerical simulation were employed. The experiment results showed that, at the end of the heating stage, the average temperature and the heat flux of FCW surface could reach 295.59 K and 29.8 W/m². Based on the test results, a numerical model was validated and then used to optimize the structure design of the FCW. The simulation results showed that a better thermal performance achieved when the insulation-to-flue ratio was 2, the smoke stopper thickness was 20–50 mm and the smoke flow velocity was 1.15 m/s-1.55 m/s, respectively.