Thermal comfort in commercial buildings is generally thought of as something that is controlled by the building's HVAC system. The perception of thermal comfort, however, is based on more than just air temperature and can be achieved more efficiently than relying only on boilers and chillers. “Thermal comfort” is determined by six variables: metabolic rate, clothing insulation, air temperature, air speed, humidity, and mean radiant temperature.
“Mean radiant temperature,” or MRT, is the average temperature of the surfaces around an occupant. Its impact on comfort is easy to understand for anyone who has sat near a window on a very cold or very hot day. Even without touching the window, one can feel the heat or cold radiating from it. While this was true with old single and double pane windows, new improvements in window technology has improved the window’s mean radiating temp and its negative impact on comfort.
The graph above shows inside glass pane temperature in summer and winter for two different windows – a high performing 925 Series SeriousWindows, and typical single pane steel framed windows. The bars on the left are much closer to the indoor temperature, whereas the bars on the right are more extreme. So a building with SeriousWindows will have better MRT.
Providing a better MRT means that heating and cooling systems can expend less energy to provide the same amount of comfort. So improving window MRT can lead to less heating/cooling needed and avoid some supplemental heating/cooling systems (e.g. perimeter heating) entirely.