When we think of green, non-depleting energy sources, most of us think in terms of solar panels and wind turbines. When prompted we also add hydropower.
There is another source, however, that I find even more attractive than wind, solar and hydro. That source is the earth. We can tap the earth to give us geothermal energy in two forms. One powers the nation of Iceland. When you live on top of a volcano, as in Yellowstone Park, you can drill down into superheated regions that turn water to steam for power. We should be happy not to have that power here because volcanoes can turn to less passive roles.
We don’t need volcanoes for the other kind of geothermal energy. It derives from the ground right under our feet. That ground stores solar energy.
Here’s the basic idea. The earth at a half-dozen feet below the surface maintains the same temperature year-round: about 50 degrees Fahrenheit. Winter low temperatures and snow don’t substantially affect that temperature, nor does summer heat. Run several thousand feet of plastic pipes through that ground and you will cool any warmer liquid passing through them to near that temperature. There is so much ground that it is able to adapt quickly to the temperature that it is absorbing from those pipes.
The application of this effect during the summer months should be clear.
Your house takes on outside heat and rises above the temperature you find comfortable. For example, you may wish to maintain your home at 70 degrees, but the temperature has risen above that. You need only transfer some of that underground coolness to your home to reduce the temperature to 70 degrees.
The system is actually a bit more complicated than that and relies on a physics law that tells us that in any closed system with constant volume, pressure is proportional to temperature. A heat pump increases the pressure in an associated vapor system, heating the refrigerant to well over 100 degrees, and this larger heat difference energizes the system.
Sounds like free cooling, doesn’t it? Well, almost. Of course the liquid must be pumped through those underground pipes and the heat pump operated. Those use electricity, but that cost is small. The system is almost three times as efficient as a standard air conditioner.
OK, we get inexpensive air conditioning. But we can also use this same system not only to heat our homes in winter but also to heat our hot water year-round. And here the efficiency is up to five times that of other systems.
For heating purposes, the vapor in the heat pump is depressurized. That drives the vapor temperature down to near freezing and the house is heated by the energy derived when that vapor is heated by the liquid circulated though the ground. Again two things power that system: the electricity that drives the heat pump and the earth that reheats the returning liquid.
Whether or not you accept that physics, this system turns out to be remarkably passive, its only cost that of the electricity it uses. It is the same kind of system that cools your refrigerator.
The real cost of geothermal heating and cooling derives from the initial installation, but much of that cost is returned today through federal and state subsidies.
No new building should be constructed without it.
*originally published in The Buffalo News