Analysis of the impact of convector heaters operating at low supply temperature on the possibility of deterioration of thermal conditions

The increasing use of renewable energy sources reduces the operating parameters of district heating networks. As a consequence, it is necessary to reduce the supply temperature of already existing building central heating systems. Therefore, there is a doubt whether such operations will not cause deterioration of the thermal conditions of rooms, in particular with a large glazing area. A balance of jet momentum fluxes was developed between the cold down draught and warm stream generated by the heater. A mathematical correlation was formulated based on this comparison. It allows to determine the minimum average velocity of convective currents of warm air generated by the heater, which protects the occupants from the undesired local cooling. The article also includes computer code to perform this calculation in a simple and quick way. A number of experimental studies and CFD modelling were performed to determine the characteristics of the convective currents rising above the typical convector heater with widths of 96 mm, 146 mm, 186 mm, and 236 mm. The type and area of the glazing, air temperature conditions, as well as the supply temperature and the size of the convector were analysed. The results of these experiments and computer simulations were presented in the form of graphs showing the impact of the most important parameters on the minimum warm air velocity value.