Human Comfort Factors - Radiant Heat

Traditionally most of the thermal comfort systems developed in the last 100 years have revolved around "air temperature" as the fundamental basis of measuring and controlling human thermal comfort. It was easy to measure and easy to control with the conventional heating and cooling devices that have been developed so far. Many of the older heating systems like cast iron radiators and wall-fin baseboard "radiators" provided some radiant heat, but predominantly they heated air and made warm buoyant plumes the dominant room heating source - they "convected" the air in the room. Cool air entered the lower part of the "radiator" and the warmed air rose and circulated in the room to replace the cool air being drawn to the bottom of the heating source. The wall thermostat controlling that "radiator" only sensed the air temperature to control how much hot water or steam entered the heating element.

Many folks working in the human comfort field recognized that radiant thermal comfort was a big part of the human comfort equation. Trouble was, though, that measuring radiant heat exchange and comfort was not easy, and required some nontraditional devices (read: expensive), so it was never pursued by the HVAC building equipment suppliers, designers and system installers.

Many human physiology studies in the past have determined that human comfort results from three fundamental factors: [ref.1, 2, 3]

• Up to 50% radiant heat exchange
• 40% convection/air movement/air temperature
• 10%-20% humidity/perspiration
  

So, what that tells us is that in order to provide a total comfort system in your home or office, you need some kind of radiant heating and cooling system, an air moving ventilation system and some form of room humidity control system. Anything less is like a car without a properly functioning engine.

Radiant comfort (and dis-comfort) is becoming better understood and studied in many parts of the world as a result of sports medicine studies, industrial applications, and military studies. Who hasn't sat beside a conventional double glazed window in a room in a cold winter climate and felt cold, even though the thermostat in the room indicated an air temperature of 74F? That cold window is acting like a large radiant cooling panel. Similarly in the summer time, the window acts like a large radiant heating panel, along with the non-thermally-broken window frame members. [Reference 4] Floor and ceiling panel heating systems have been well known and in wide use for some time, and are generally well understood. The radiant floor heating i...