Effects of radiant asymmetry on the thermal comfort conditions: Experiments in a test room

Occupants' well-being in buildings is related to the thermal comfort conditions in indoor spaces. Radiant asymmetry is a parameter of localised discomfort and its evaluation is rather challenging. It should be considered when dealing with radiant systems since they could produce unacceptable asymmetric temperature fields. In this paper, the issue of radiant asymmetry in winter is experimentally investigated in a test room equipped with radiant panels. A first round of testing is carried out to study the limits in terms of supply water temperature of the heated surface in relation to the discomfort curves proposed in the current standards. Configurations with a heated wall or ceiling and the contemporary presence of one or more heat-dissipating surfaces are considered. Twelve scenarios representing real building situations are analysed, each involving three consecutive heating phases with increasing supply temperatures of 30, 35 and 40 °C. The most critical configuration is imposed in a second testing round with 8 participants checking the actual subjects' perceptions through questionnaires, with conditions of global thermal neutrality (PMV = 0). The scenario with a heated ceiling and heat-dissipating floor is the most adverse, generating a vertical asymmetry exceeding the standard limit of 4 °C when the supply temperature is above 35 °C. The survey campaign shows that uncomfortable cold sensations are prevalent with lower radiant asymmetry levels, whereas the highest ceiling temperature improves comfort perception. The results suggest that participants could not feel the asymmetry increment and analysis of radiant asymmetry discomfort should also consider surface temperatures along with plane radiant temperature difference.