Geothermal for the Farm

T-bone!

Have you heard about geothermal?  It’s a simple heating and air-conditioning technology that’s been around since the 1940s.  And it’s super-efficient.  The most efficient gas furnace is 94% efficient, but a ground source heat pump (geothermal) is 400% efficient!  That’s because a ground source heat pump uses a little energy to go get a lot of energy from the ground.   In our quest for low-to-no bills, we’re very excited to have geothermal in our home.

trenching

A ground source heat pump pumps a water/antifreeze mix into a pipe loop that’s buried in the ground.  Like a cave, the ground is cooler than outside air in the summer and warmer than outside air in the winter.  I like to think of geothermal heat and air as renewable energy because it’s using free energy from the ground, and that free energy will always be there. 

In the summer, the heat pump uses electricity to pump the water mix into the ground loop.  The water mix coming out of the house is hot – it contains the heat that we’re trying to get rid of in the summer.  As the water mix travels through the ground loops, it cools because the ground is about 55 degrees.  That cool water returns to the house, and the heat pump delivers cold air to the home – air conditioning!  It works the same in the winter, except the water mix leaving the house is very cold, and it gets warmed up when it travels through the ground. 

Trenches were 220' long each.

We’ve been really interested in geothermal for a long time, so interested that we scrounged around and drove all the way down to Georgia to get a great deal on a 6-foot blade Ditch Witch.  One look at the beast, and we named it “T-bone”.   We used T-bone to trench four trenches that were 220 feet long and 6 feet deep each.  We laid black water pipe in the trenches – 6 feet down going away from the house and looping back at four feet down coming back to the house.    We pushed the dirt back into the trench and tamped it hard so the dirt would have great thermal contact with the pipe (the water mix will cool/heat faster).  All the pipes are connected together in a manifold and brought back to the house.  The total length of pipe is about 1,780 feet.  The water mix will travel that whole length before returning back to the house.

Next steps are duct work and installing the ground source heat pump inside the house.  With a small house, loads of insulation, and geothermal heating and air, we’re really excited to see how low our electric bill will be.  Wish us luck!

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4 responses to this post.

  1. Posted by Keith on August 26, 2010 at 5:04 pm

    The heat and air system that was in the Twin Towers was very similar. Used water from the Hudson. I was told there was a floor four stories below street level that contained heat exchangers used for the process.

    Our company has built several exchanger trains for geothermal situations. It’s pretty interesting stuff, eh?

    Reply

  2. Sounds awesome. How long will it take to capitalize the cost?

    Reply

    • This totally depends on the existing system being replaced and the efficiency of the house (insulation, good windows, etc). Our old farm house didn’t have central air and heat to begin with, and we saved so much on labor (we did the duct work too), we’re not really comparing the cost of installing our geothermal system to anything else.
      Typically though, an average size home will see a 60% reduction in its heating/cooling bill. So, if your average bill is $200 per month, you’d save $120 per month or $1,440 per year. If the difference between a conventional system and a geothermal system is $5,000, it would take less than 4 years to be in the black ($5,000 / $1,440 = 3.5). Higher bills would give a shorter recovery period.

      Since the ground water loop will last 100 years or more with only the heat pump and circulation pump needing replacing after 10 years or so, the savings benefit continues indefinitely.

      Reply

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