Comfort limit for asymmetric thermal radiation from a cold wall in neutral to cool environments

Asymmetric thermal radiation from a cold surface, could easily cause local thermal discomfort and even health problems, such as knee osteoarthritis. An experiment with subjects was conducted to study the radiant asymmetry caused by a cold wall at a room temperature of 18 degrees C, which is the lower limit of the room temperature for heating design in Chinese Building Regulations. The temperature of a single wall was set at 15 degrees C and 12 degrees C respectively to simulate a cold exterior wall or window. A control experiment was also conducted under uniform chamber conditions. Groups of 24 healthy college students participated in the experiments. During the first 30 min of the 90-min experiment, the participants could adjust their clothing to approach thermal comfort. The skin temperatures and thermal perceptions of the subjects were measured. The results indicated that clo-value for participants increased with the decrease of the temperature of the cold wall. The skin temperatures and thermal sensations of the limbs were significantly lower than these of the upper torso. The skin temperature of the calf was the lowest. The prolonged exposure to the cold wall decreased the acceptability of the subjects. Accepting 5% of the subjects expressed local discomfort, the acceptable radiant temperature asymmetry was 4.2 K. The limit value obtained in this experiment was significantly lower than the limit value recommended in the existing standards. The lower acceptable value of radiant temperature asymmetry from this study can provide a relevant input to a revision of existing thermal comfort standards.