Study On Convective Heat Transfer Coefficient At The Cooled Radiant Water Based Surfaces

As a new type of energy saving and comfort air-conditioning, radiant cooling technology has been attracting more and more attention. As one of important thermal parameters,the heat transfer coefficient of radiat panel have been used to study the thermal performance、 dynamic heat transfer processes and built mathematics model. It played an important role in the research of engineers as well as scholars. Presently,the research on the radiant heat transfer coefficient of radiat panel has matured, the research on the convective heat transfer coefficient is relatively insufficient, some experience data lead to a lot of errors in thermal calculation and building energy consumption analysis. In this article, the convective heat transfer coefficient was studied, the heat flux of radiant panel were analyzed, new correlations for convective heat transfer coefficients and the main influence factors were analyzed.Firstly, system forms of different types of system have been described in detail and compared. The important features have been analyzed in detail, such as working principle, thermal comfort, energy consumption and so on.Secondly, the simplified calculation methods to determine cooling capability of the different types of water based surface cooling systems was described, the cooling capability of the ceramic surface was calculated. The cooling capability of the cooled radiant water based surface was calculated when the convective heat transfer coefficient was different. The influence of convective heat transfer coefficient on the cooling capacity was analyzed. The results show that when the convective heat transfer coefficient is increased, the heat flux of cooling radiation panel will be increased. Especially when the cooling tube diameter and tube spacing are smaller, the effect will be more obvious. In the case of the cooling pipe diameter is 10 mm, the tube spacing is 50 mm, when the convective heat transfer coefficient increases from 0.1W/m2?K to 5.5W/m2?K, the cooling capacity can be increased by 56.7%.Thirdly, the numerical models of radiant cooling combined with air supply systems were built, the ten assembly cases that the terminal units of radition cooling system were in ceiling,floor,side wall, and the terminal units of air supply system were in topside, underside,side,floor were numerically simulated. The convective heat transfer characteristics between the cooling panel and indoor air were studied. New correlations for convective heat transfer coefficients at the surfaces were found in the current study. The results show that the convective heat transfer coefficient is inversely proportional to the distance between cooling panel and air layer. The convective heat transfer coefficients of ceiling cooling are highest, The convective heat transfer coefficients of floor cooling are lowest. When the air velocities are 0.2~2.0m/s, the convective heat transfer coefficients of ceiling cooling, wall cooling, floor cooling about are 1.21~4.47W/m2?K, 0.47~2.59W/m2?K, 0.25~1.21W/m2?K.At last, the main influence factors were analyzed, such as the temperature difference between the radiant panel and indoor air, the position of cooling panel or inlet air velocity and so on. The results show that the convective heat transfer coefficient is proportional to the air velocity. The convective heat transfer coefficients of ceiling cooling are about 70% higher than the convective heat transfer coefficients of floor cooling, about 45% higher than the convective heat transfer coefficients of wall cooling.