A method for judging the overheating of the radiator in the compensation of window downdraught based on thermal image velocimetry

Abstract

To prevent the downdraft of windows, the radiator heating temperature needs to be sufficiently high. The prevailing method of estimating the radiator temperature is based on the principle that the reference velocities of natural convective flow over the radiator and window are comparable. However, this method overestimates the heating temperature, which may be too high due to the existence of an overheating mode. This study analyzed the change rule of the airflow field over a radiator in a window-wall radiator heating system based on thermal image velocimetry(TIV). A second-order polynomial composed of the reference velocities of the window and radiator was fitted to represent the change law of the airflow velocity near the exterior wall between the radiator and window. This correlation can be used to judge whether the overheating mode exists based on whether the calculated velocity approaches −0.1–0 m/s. The momentum of the downdraft along the window and that of the thermal plume along the radiator are calculated based on the semi-empirical correlation in the literature. When the momentum of the downdraft and thermal plume is balanced, an overheating mode exists. Additionally, a correction coefficient related to the radiator structure, whose value is within 1.057–1.309, is multiplied in calculating the momentum of the thermal plume. The correlation in the form of y = axb is established between the TIV results and the maximum velocity within the boundary layer, calculated from literature's semi-empirical correlation. The results of this study will be useful for increasing the efficiency of heating systems.