The Intricacies Behind Thermal Comfort

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.

Can We Design Buildings for Heat and Cooling that Mimic the Human Body

Lucas Hamilton

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation

I spend lots of time thinking about buildings. Sad; I know. Lately I have been wondering how we wound up in such a confusing state. It’s like looking under your car hood. Have you looked under your hood lately? It looks like a building design. Who in their right mind would have started out to design such a complicated mess? No wonder we need so many building scientists and we pay a hundred bucks an hour to get our cars fixed. Can we step back for a minute?

Thermal comfort in the built environment needn’t be so complicated. If we could start from scratch and try to make buildings comfortable based upon our own organic experience, what would we do? I live in Philadelphia.  If I go outside in the winter and try to passively stay comfortable – passively meaning to not use any outside energy sources – I would use lots of layers of clothing, would zip up tight and cover my skin.

Coincidentally that is what we require in our cold climate building codes.  Lots of layers of clothing means R-value. When you wear lots of layers of clothing you are trapping gas inside layers.  The gas is the insulation – gas gives you resistance to conductive energy heat flow – that’s R-value.  So when you are wearing lots of layers you are wearing R-value. When we say zip up – that’s getting air tight. We finally woke up and added that one to the cold and mixed climate codes as well.

The problem comes in the summertime. To stay cool, you would take off those layers, wear light colors and try to get air flow around you.  You would wear airy fabrics to release as much heat from your body as possible and light colors which don’t get hot in the sun. If you were stuck wearing lots of layers and were zipped up tight, you would have to blow cold fresh air into that outfit to stay comfortable. Our goal should be not to do that. Remember, passive technologies rule and active technologies cost $$$.

We need to find ways to help a building be warm in the winter and stay cool to begin with in the summer. I am looking for changes to our practices that will enable us to do to buildings what we do to ourselves. How would you build your building differently?

If you can’t strip off all the layers of clothing the very least you will do is unzip so can we figure out a way to unzip our buildings? I know we want to be air tight in the winter but can we figure out a way to use air to remove surface heat in the summer? I think ventilated claddings may be one answer.

Can you think of some others? To go back to the car analogy, let’s stop bolting more stuff onto the internal combustion engine to make it more efficient and drop in an electric motor. It needn’t be so complicated.