Defining human comfort

A heated debate

Why can't we all agree on a perfect temperature setting? There are several factors that contribute to human comfort that you may be unaware of. 

The complexities of comfort

If a thermostat reads 70°F (21°C), will everyone in the room be comfortable? Probably not. The temperature of the surfaces around you, air speed coming out of your vents, humidity and air temperature are factors that your heating or cooling systems can address. Your clothing and metabolic rate also contribute to your comfort. Together, these are the six primary factors that influence human comfort.

The prime example of the complexity of human comfort are those clear plastic boxes that you can buy to put over your thermostat. Chances are you have seen one of these in a store or may even have one in your office. The reason they sell these little, clear plastic bank vaults is because a group of people rarely agree on a specific thermostat setting.

With forced-air heating and cooling, you aren’t actively controlling surface temperature, which is one of the six primary factors that determine human comfort. If your primary source of heating and cooling is radiant , you can adjust the actual surface temperatures of the objects in a space by emitting or absorbing heat through a network of PEX pipes hidden in the floors, ceilings or walls. By changing the temperature of the surfaces around you, less of your comfort depends on the temperature and velocity of the air in a room. With radiant, you can control more human comfort variables.

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Picture yourself talking to your neighbors at a barbeque. You are standing in the shade of a tree on a fall day. You feel a little chilly and decide to step onto the concrete driveway in the sun. You immediately feel warmer. The air temperature didn’t change; the temperature of your surroundings changed. Not only is the warmth of the sun radiating on you, but you are also standing on concrete that has absorbed heat all day and is radiating heat back to your skin. Floors with radiant heating inside your home have a similar affect. The ability to control surface temperatures has a powerful impact on your comfort.

Need the technical details? 
If you are looking for more of the technical details for how all the human comfort factors influence each other, the Center for the Built Environment, University of California Berkeley, has a tool to help heating and cooling system designers calculate what discomfort may be. It is based on ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy criteria. If your calculated point falls outside the purple area in their chart, you may be headed for discomfort.

Visit our website to learn more about radiant technology.

By Max Rohr, manager, REHAU Academy

Engineering progress

Enhancing lives

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