Already being used in many places around the world, the idea of using human body heat to keep buildings warm during cold seasons gains popularity very fast. After many studies engineers concluded that excess body heat could slash carbon emissions in urban areas by one third, if collected and used properly.
You may have noticed that, when you’re in a subway station or in a crowded supermarket there is always a strange warmth in the air. That’s the heat generated by the people around. Even if it’s hard to believe that such a heating source could be enough to keep a building warm, examples prove that the technology is applicable and really effective.
To better understand how this technology works, I think you need to know first how we humans generate all that heat. There are four different ways we lose our body heat (radiation, conduction, convection and evaporation), so let’s talk a little bit about each of them:
Radiation: It happens only when the temperature of our ambient environment is lower than 37 Celsius degrees. Just like the sun or like an open fire, our body transfers its heat to the environment by thermal radiation (the emission of electromagnetic waves in the infrared spectrum).
Conduction: With some minimal knowledge of physics you should know that when a warm body makes contact with a colder one, the heat will flow between them (molecular heat transfer) until they reach the same temperature. Conduction is responsible for only 2% of the entire heat generated but when our clothes get wet heat loss is 5 times faster.
Convection: In this heat transfer process one of the objects is moving. When air molecules around our body are filled with energy (heat), they flow away, letting other molecules to be heated. In this process, the energy transfer rate depends on the fluid type (or fluid density). So, in water we lose heat much faster.
Evaporation: Perspiration is the body’s natural response to excess heat. So, when that water changes from liquid to gas, we lose heat. The evaporation process is possible only with heat absorption (it is an endothermic process).
Knowing these things about human body, engineers used heat exchangers to transfer the heat from the most crowded urban places into near buildings or homes. Some may consider this idea a waste of time but as long as it saves significant energy and makes the environment cleaner, I think it worth a try.
Like I said before, this technology is already used in many places around the world (France – Paris Habitat, Minnesota’s Mall of America or Stockholm’s Central Station) and I think it represents a major step towards greening the world.