Geothermal Heat Pump Guide

It really shouldn't be called Geothermal; that should be reserved for volcanoes and geysers. But that is what everyone is doing these days. It is popular and efficient because it moves heat instead of making it, which is a lot more efficient. Really, it is a form of solar power, picking up energy that has been stored in the ground after being warmed by the sun.

What is Geothermal Heating and Cooling?

It is basically an air conditioner that can run backwards, and that uses the ground as its transfer medium instead of the air like a traditional air conditioner. Because the ground is much denser than the air, it is much more efficient as a medium. Just like your fridge, a compressor moves heat from inside the box to outside, where the refrigerant condenses and transfers the heat to the stuff surrounding it. But instead of mounting the coils on the back of the fridge, they are buried in the ground. It is that simple.

What it is NOT:

Geothermal. Many engineers (and me) reserve that term for direct heating from sources like geysers and volcanic rock. The Canadian industry adopted the term "geoexchange" to present a term that was sexier than GSHP.

Why we like Geothermal

It is very efficient, often delivering 300% efficiency on the electricity put into it to run the pumps. When used for cooling, it eliminates the noisy and inefficient condensers that conventional air conditioners have. When used for heating, it is essentially using solar power, transferring the energy that the ground has absorbed from the sun to your home.

An air conditioner or air cooled heat pump tries to pump heat into warm air, or squeeze it out of cool air. A ground source heat pump (GSHP) uses water or a glycol solution, with the ground as an exchange medium. There is a lot of capacity to absorb heat in the cooling season, and a lot of heat to move in the heating season.

What we worry about

It isn't cheap, and is being pushed hard right now as part of the weatherization programs in the States and the renovation grants in Canada. The money might be better invested in insulation.

It is electric powered, and when you take into account the inefficiencies of the electrical distribution system and the fact that so much of American electricity comes from coal, conversion of a gas furnace to a GSHP system might actually increase greenhouse gas output in certain parts of the country.

But the biggest worry is the addition of heat pump systems to homes that previously got along just fine without air conditioning. Suddenly people have a very convenient way to keep cool all summer, and might actually increase their energy use.

Eco-factor of Heating and Cooling

In any part of the country reliant on oil or electricity, conversion to a GSHP system is going to save a lot of money on operating costs and reduce greenhouse gas emissions.

Cost of Heating and Cooling

Varies significantly, depending on the ground that the pipes have to go into and the way they are installed. Sometimes they are trenched; others drill straight down; lucky people beside lakes can just throw them in the water. Some have said that costs can be as low as $10,000 but most installations cost two or three times that.

More reading:
Blowing Hot and Cold on Ground Source Heat Pumps
Jargon Watch: Geothermal vs Ground Source Heat Pump
Jargon Watch: Geothermal vs Ground Source Heat Pump
The Tipping Point for Geothermal Heating and Cooling?