Heat pump design
What kind of heating system makes sense these days?
There is so much hype about geothermal heating and cooling systems these days; there is even talk of declaring Oct. 20 to be National Geothermal Day, “to raise awareness about environmental and economic benefits of geothermal energy and its vital role in building a clean and secure energy future.”
This is the first problem, because geothermal is the name for a really important renewable resource, the "the thermal energy contained in the rock and fluid (that fills the fractures and pores within the rock) in the earth's crust." There is a future for real geothermal in America, so the terms shouldn't be mixed up. (for more information, see here at the Geothermal Resources Council.)
What they are really describing is what's known as a ground source heat pump or GSHP. Here is the definition of each:
- Geothermal systems use heat directly from natural sources like hot springs, geysers and volcanic hot spots like the installation on the right in the Iceland photo above.
- Ground source heat pumps are air conditioners that use soil or groundwater to cool the condenser instead of an outside coil and fan. It uses electricity to move heat energy from one place to another. Run it backwards and it provides heat, and more efficiently than using electricity directly.
I've gotten myself into a lot of trouble criticizing GSHP systems in the past; a common response when I write is that I don't know what I'm talking about; this is my favorite: "If I were a geothermal contractor or manufacturer I would have asked that this be removed for falsely conveying what geothermal has to offer." That was seven years ago, and frankly the water has just got muddier since. There are so many myths and misconceptions about GSHP systems, many of which can be found on the National Geothermal Day page. These include:
Geothermal is a clean (no fossil fuel consumption) form of renewable energy that involves our sun heating the earth beneath our feet.
GSHPs are powered by electricity and in America, 46 percent of the electricity is generated by burning coal, a fossil fuel.
Through a geothermal system (geo for earth and thermal for the heat from the sun), we use that energy in the ground to heat and cool our homes.
When a GSHP is in heating mode, it is indeed extracting heat from the ground and that heat can be assumed to be from the sun, or from the natural heat from radioactive decay in the core of the planet. However in cooling mode, the GSHP is pumping heat into the already warm ground and there is zero gain of any kind from solar energy. In cooling mode it is nothing more than an air conditioner using the ground as a condenser. Do you think your AC unit runs on a renewable resource?
Geothermal is the most efficient form of heating and cooling that exists.
No it is not. That would be passive solar heating in a house with a lot of insulation and careful design.
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