Human Comfort is Best Delivered by Water Not Air

Lucas Hamilton

While attending the Regenerative Network conference in California, I spent time in a LEED platinum certified building which is radiantly heated and cooled.  Recently, I have been giving presentations on human interactions with their environment. This has caused me to consider how differently the radiant heating and cooling system in the David Brower Center influences our perception of comfort.

We understand certain things about human senses such as how temperature, humidity, air speed and radiation are inter-related and together influence our perception of our surroundings.  These are the four things that will dictate how comfortable you are.  Because these things are inter-related, the way that heating and cooling is delivered has a huge influence on how you perceive your comfort level. As background and in simplified terms, these energy delivery methods are conduction, convection and radiation. A pot on the stove is conducting heat, when you pull out the spoon and blow on it to cool it is convection, and radiation is when you can stand a few feet away from the pot and feel the heat.

We traditionally heat and cool our buildings with air.  This is a most inefficient method. The idea of trying to store energy in something that has little mass makes little sense.  Using water to deliver energy as a way to comfort is very, very efficient.  This gives you radiated comfort as opposed to convection or conducted comfort.

To achieve the desired goals in energy savings delivering comfort by air may be on its way out. Using water to heat and cool buildings is a far more efficient method and it will save lots of energy going forward. But, we will have to make some personal sacrifices to accommodate this change. We may have to give up on instant gratification and develop patience through acceptance.

If you are outdoors on a cold day and enter a warm building, it will take awhile for the body to warm again to where you would say you are comfortable. However, after walking outdoors on a hot, humid day and entering an air conditioned building the cool rushing air will evaporate the sweat on your body and you cool off very quickly.  It’s like the building is blowing on the hot spoonful of soup.  When you condition a building space using surface temperatures, the energy exchange between the building and the person becomes largely dominated by radiation. While this will cool you down by allowing excess energy in the form of heat to flow out of your body and into the building through radiation, it will not be nearly as quick a process as having cold air blowing across your sweaty skin. Chances are you will continue to sweat for a few minutes after you have come inside so be ready for it.

Being patient and waiting for the comfort to occur is a small price to pay in order to make our energy go further. It sounds like a contradiction to say “exercise patience” but there you have it.

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation

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