The Intricacies Behind Thermal Comfort

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When you think about thermal comfort, what comes to mind? Insulation? Heating and cooling systems? The thermostat? Of course, these are all critical components to interior spaces that are conducive to happy, productive occupants. However, to truly master the science of thermal comfort, a more in-depth investigation can be beneficial.

While radiation, air speed, and humidity might be the most studied aspects of thermal performance, let’s shift our perspective to that of the end user. Specifically, how do activity, age and clothing affect comfort in interior environments?

Believe it or not, studies by ASHRAE indicate that clothing has very little impact on comfort. To reach this conclusion, ASHRAE used a unit of measure, clo, to determine the insulating capacity of clothing. Clo is based on the amount of insulation that allows a person at rest to maintain thermal equilibrium in an environment at 70 degrees Fahrenheit in a normally ventilated room. The difference in clo, which equates to 0.88 r-value, between summer and winter fashion selections is roughly 1.5 clos — a miniscule factor in terms of comfort.

However, when you consider the age of occupants it’s a different story. A 25-year-old employee bouncing off the walls and drinking a Red Bull experiences comfort much differently than a 50-year old manager who sits at a desk 8-plus hours a day.

Why? The rate of metabolism, which is influenced by age among other things, can create an awful lot of heat.  Since heat production varies from person to person, individual actions are taken to reach equilibrium that impact the entire space, such as opening a window, allowing more sunlight into the area or adjusting the thermostat.

The lesson here is that architectural professionals and building owners should be mindful of age in their designs to ensure long-lasting comfort for building occupants. For those of you that want to take a deep dive into the nuances of thermal comfort, check out ASHRAE 55-2013.

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About Author

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation

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