Our House 5: Geothermal Heating

Our House 5: Geothermal Heating

I have been really into geothermal heating for some 15 years now. I remember talking with a coworker about geothermal when they were building 15 years ago, but they decided not to. Since then, I’ve wanted to use geothermal heating.

What is Geothermal Heating and Cooling:

The simple answer is that geothermal relies on the near constant 55 degrees below ground. The ground acts as a heat sink, and we can draw that heat up in the winter time to heat our homes, and we can sink heat into the ground when we need cooling.

In Minneapolis proper, we would have drilled a few 200 foot deep wells, put a coil of tubing in each one, and circulate water / antifreeze mixture into the coils. They would be warmed to 55 degrees, and put into the heat exchanger in the basement of the house. The heat exchanger would draw off the heat and transfer the heat into water that circulates in the radiators, or in-floor radiant heat tubes. Then the cold(er) water would be circulated back to the wells to draw more heat.

In the summer time, we would extract heat from the rooms using a heat exchanger, which would put the heat into the tubes in the well. The warmer water would go into the wells and would be cooled down to 55 degrees, where it would circulate back into the heat exchanger.

In new construction, or places where there is a larger lot, instead of wells, you would dig up the field, and put the coils of tubes in the ground and bury the loop. That field would end up being the heat sink.

Benefits of Geothermal heating and cooling:

The main benefits are reduced cost of operation, as well as not burning natural gas because the heat pump relies only on electricity. The reduced cost of heating and cooling comes from the fact that you extract the heat from the existing ground heat, rather than burning natural gas. If we call a furnace 92% efficient, geothermal heating is somewhere in the range of 300% efficient.

The fact that we wouldn’t need to burn natural gas is also a great resource saver. With solar panels, and geothermal heating, one could almost be “off grid”. Cool.

Why we didn’t do geothermal:

I tried to find a contractor to do geothermal heating in our house, but couldn’t There wasn’t a history of doing geothermal heating in Minneapolis, back in 2005 / 2006. I have since seen 2 installations of geothermal heating in Minneapolis, both on corner lots, which are somewhat larger than the standard 40 foot wide lot.

That being said, I got 3 bids for heating in our house. The first was to extend the boiler heat to the second floor, and add a/c cooling for both the second floor, and the main floor.

The second bid was to put in a standard furnace in the second floor that would only heat the second floor, and it would cool BOTH floors. New ducts would be in place to serve both floors, with dampers that we will change spring and fall to switch from heating to cooling. The existing central air unit in the attic and that will be removed.

The third bid was the same as the second bid, but a higher bid price.

We ended up going with the second bid, adding a forced air heating and cooling system to the existing boiler heating system. This system would be contained in the attic space of the second floor. Our prior house had a similar system, so we weren’t unfamiliar with running two systems.

One main advantage to having two heating systems is that you have built-in zones. We can control the heat on the second floor separately from the heat on the main floor, with each floor having its own thermostat. That means we can optimize usage between the floors, turning down the heat on the second floor during the daytime when nobody is upstairs, and turning down the heat on the main floor just after supper time. So that’s how I have the thermostats programmed.

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