Research On The Dynamic Variation Characteristics Of Radiant Panel Surface Temperature

The heat transfer of radiant ceiling cooling system is radiation mainly, coupling with convective heat transfer. Radiant ceiling cooling system has been gaining much popularity due to high thermal comfort and energy saving properties. When the surface temparture of the panel was lower than the dewpoint temperature of the moisture air near the panel, the condensation may occur on the surface. This phenomenon is the primary obstacle that limitted its widely use. The surface temperature of radiant panel is one of the key factors that impact condensation of the radiant panel surface in radiant cooling ceiling system. The heat transfer of radiant ceiling consists of three steps, the convective heat transfer between coled water and tube wall, the conduction of radiant panel, the both radiant and convenction heat transfer between the surface of the panel and the environment arround. The dynamic variation of radiant panel surface temperature is the theoretical basis of anti-condensation control. This paper using experiment and simulation methods to analyze the comprehensive impact of supply water parameters and thermal environmet parameters on the surface temperature of radiation panel.This study anlyzes the impact of indoor person number, supply water temperature and water flow on the surface temperature of radiant panel using experimental method. The experimetal results show that:(1) the surface temeperature of ceiling is uneven and the surface temperature is high which is closed to the window and heat source,and it is lower that of the panels which are colse to the supply water. The impact of indoor person number on the surface temperature is not significant. However, with the increase of person number the dew point temperature of the attached layer increased obviously.(2) When the supply water temperature increases the surface temperature rises as negative exponential. The higher supply water temperature is, the higher the surface temperature of the radiation panel becomes when the temperature is stable. With the increasing of supply water temperature and surface temperature of radiant panel, the temperature difference between the surface and the dew point becomes larger which is larger than 3.3℃ in different cases and it can prevent condensation.(3) The on–off control method can make the surface temperature increase quickly and the difference between surface temperature and dew point temperature increases gradually. When supply water flow decreases, the panel temperature increases less and its anti-condensation effect is poor.(4) Compare the two methods, it can be found that: when the supply temperature increases the surface temperature increasing rate is higher than that of water flow control method. The surface temperature increasing rate decreases quickly when the water temperature increases and it decreases slowly when the water flow was reduced.Based on the experiment results the comprehensive impact of different factors on the surface temperature of radiant panel was analyzed using simulation method. Then, the simulation resluts ware analyzed using regression analysis prediction method of SAS to obtain the relationship between surface temperature and the factors when the water temperature and flow rate keeping at 16℃and 0.366m3/h. The results show that the impacts of solar and person number on the surface temperature are not significant. Based on this, further study was done on the surface temperature variations of the water temperature and flow regulation processes and obtained the regression equation between panel surface temperature and other factors. The results show that with the increases of water temperature, the surface temperature increases as negative exponential. When the flow valve was turned off, the surface temperature of radiant panel increases gradually. And the surface temperature of panel decrease as negative exponential gradually when the water temperature and flow was set to the design value again. The surface temperature changing rate are close in both cases of water temperature incerasing and decreasing. When the flow valve was on again, the surface temperature decreasing rate is higher than the increasing rate when the flow valve was off.This study analyzed the comprehensive impacts of supply water parameters and thermal environmet parameters on the surface temperature of radiation panel using experiment and simulation methods. The dynamic variation characteristics of radiant panel surface temperature are obtained. The achievements of this study establish the theoretical basis of anti-condensation control.