On the measurement of the mean radiant temperature and its influence on the indoor thermal environment assessment

The mean radiant temperature is one of the six main variables responsible for the thermal sensation of the man exposed in a particular thermal environment (indoor and outdoor). Its measurement is not direct and is usually carried out by means of different methodologies and instruments whose general details and accuracy requirements are reported in the ISO Standard 7726. This paper deals with a critical review on the typical measurement methodologies combined with a comparative analysis of the metrological performances exhibited by the more common practice instruments on the market. To this purpose a special room-test has been designed aiming to reproduce the typical microclimatic conditions can be encountered in workplaces both in summer and in winter conditions. The effect of the measurement methodology and used instruments on the thermal comfort (global and local) and the thermal stress assessment has been finally discussed. Obtained results show that the use of different instruments consistent with ISO Standard 7726 requirements results in values of the mean radiant temperature compatible with each other, but the consequences on thermal environment assessment appear often ambiguous. Obtained results have focused the need for starting an in-depth discussion on the measurements’ protocols and the instruments leading to a possible reduction of the required accuracy levels reported in the ISO Standard 7726.

► We have investigated the measurement methods of the mean radiant temperature.
► Measurements have been carried out in a test room reproducing moderate conditions.
► The method based on the angle factors is reliable.
► The method based on the net radiometer is often not compliant with other methods.
► The assessment of both global and local comfort can become quite random.