Research On Low-temperature Hot Water Wall Radiant Heating System

The heat transfer characteristic of low-temperature wall radiant heating systems is different from the low-temperature floor radiant heating systems or the low-temperature ceiling radiant heating systems, thus the heat load and thermal comfort is different on condition even the indoor and outdoor temperature differences in both cases are same. However, researches on low-temperature wall radiant heating are seldom reported, so study of its comfort and thermal characteristics is urgently needed.Based on the established model of a room with wall radiant heating system, the influence on heating of the heating tubes layout and the tubes outer surface temperature is probed into by numerical method. The results show that the heat released increases linearly with the temperature of the tubes outer surface increasing. When the tubes lay centered on the wall, the total thermal output is the minimum. While total amounts of heat released are similar for both cases of the tubes lay upper and lower zones on the wall. The total heat released increases with the radiant pipes spacing increasing, but the increasing amplitude gradually decreases.This paper also analyzes the Predicted Mean Vote (PMV) and the Predicted Percent Dissatisfied (PPD) of the room with the low-temperature floor radiant heating systems with different heating tubes arrangements. The results show that the heating system position has the most significant impact on the indoor thermal comfort. The indoor thermal neutral zone expands with the tube spacing increases. It is mostly comfortable near the floor when the tubes locate on the lower zone of wall. By contrast, it is mostly uncomfortable near the floor when the tubes locate on the upper zone of wall. This paper has calculated the tubes outer surface temperature needed and the total heat release when the room reaches a most comfortable state with different heating tubes layout. Results show that the room reaches a comfortable state with the lowest energy consumption when the radiant system is in the center zone of the wall. The tubes outer surface temperature needed for a room reaches a comfortable state decreases with radiant pipes spacing increases.Finally, the paper analyzes the heat released of the heating tubes. The power fitting form is used to fit the heat released variation with the temperature difference between the tubes outer surface and the indoor air. Fitting parameters with different tubes layout are also determined.