DA-13-008 -- An Infrared Sphere Method to Measure Mean Radiant Temperature PDF

The mean radiant temperature (MRT) of a given thermal environment is an important environmental parameter that influences the thermal comfort of occupants. The MRT is typically measured by the black globe or surface temperature methods. However, the response rate of a globe thermometer is slow to document rapid HVAC system operation or external factors such as solar incidence. It also requires additional sensors to measure the air temperature and velocity to derive the mean radiant temperature.

The surface temperature method is faster due to the quicker response of the sensors. But a quantity of sensors is required to measure surface temperatures at a number of representative locations in order to calculate MRT. This method is contingent on the surface temperature uniformity and may be impractical for large or spaces for limited available sensor lengths and interference with the lifestyle of the occupants. Using an infrared (IR) camera to monitor surface temperature is less intrusive, but the difficulties of view factors, sensor deployment, and accuracy remain.

A device based on the actual reception of radiant energy to determine the MRT similar to the black globe, but with a quicker response time, is desirable. In this study, an infrared sphere device was developed to measure the mean radiant temperature. The device was deployed at two test building sites against the surface temperature method and the black globe method in determining MRT. The results show that the infrared sphere device developed is fairly accurate, affordable, and robust.