Evaluation of the thermal performance of radiant floor heating system with the influence of unevenly distributed solar radiation based on the theory of discretization

In the building with many transparent envelopes, solar radiation can irradiate on the local surface of floor and cause overheating. The local thermal comfort in the room will be dissatisfactory and the thermal performance of radiant floor will be strongly affected. However, in many current calculation models, solar radiation on the floor surface is assumed to be uniformly distributed, resulting in the inaccurate evaluation of the thermal performance of the radiant floor. In this paper, a calculation model based on the theory of discretization and the RC thermal network is proposed to calculate the dynamic thermal performance of radiant floor with the consideration of unevenly distributed solar radiation. Then, the discretization model is experimentally validated and is used to simulate a radiant floor heating system of an office room in Lhasa. It is found that with the unevenly distributed solar radiation, the maximum surface temperature near the south exterior window can reach up to 35.6 °C, which exceeds the comfort temperature limit and is nearly 8.5 °C higher than that in the north zone. Meanwhile, the heating capacity of the radiant floor in the irradiated zone can reach up to 171 W/m2, while that in the shaded zone is only 79 W/m2. The model with the assumption of uniformly distributed solar radiation ignores the differences between the south and north zones and fails to describe local overheating in the irradiated zones. By contrast, the discretization model can more accurately evaluate the thermal performance of radiant floor with the influence of real solar radiation. Based on this discretization model, novel design and control schemes of radiant floor heating system can be proposed to alleviate local overheating and reduce heating capacity in the irradiated zone.