Trouble Choosing a Home Geothermal Energy System



Geothermal heating and cooling systems have been a topic of conversation for many of my high-performance building projects over the years. I recently came across a project that I thought might be a good fit for geothermal.

This article does not cover the difference in the heating systems. The point of this article is for the reader, to recognize not only the breakdown in information between the leading companies in our area, but also to recognize that we wanted to find the most efficient system for this project. A solid long-term choice would be one that examined what technology currently exists and if that system can be upgraded to be more efficient in the future.

This particular project was a remodel that included an addition. The project sounded like it may be a good fit for a geothermal heating and cooling system, so I inquired about who the builder was. The homeowners replied that they might be looking for a builder and I said that I was interested in being involved. I was very interested in seeing how a geothermal system may work in this project and was excited to be selected as the builder of this project.

Exploring Options for Home Heating

As the project progressed, the homeowners and I decided that it was time to meet with a heating contractor to discuss which heating system would be a best fit for the project. I have always been a fan of reviewing options, so the first heating company representative showed us multiple systems, which included: upgrading the existing propane-fired forced-air furnace with air conditioning, a mini-split systems, an open-loop geothermal system and a closed-loop geothermal system.

I have learned throughout the years that there is not a magic one-size-fits-all solution to heating and cooling in a home. My hope here was that geothermal was going to be the best value versus performance for this project. The homeowners had heard that geothermal was the most efficient heating and cooling system available, and we were going to rely on the heating and cooling company to show us the performance data to see if that was correct or not.

11/11/2019 5:56:14 PM

An interesting article Adam.  Believe it or not but I have a ground source heat pump in my home as a backup to my outside wood boiler.  My Geo system was not large enough to heat my new workshop so when I decided to put in the boiler I tied it into the Geo system in my home to heat both buildings.  It wasn't until I tried to help a friend decide on a new heating system for his house that I truly came to understand how important the engineering work is for a Geo system to function at peak efficiency.  You made a comment about one sales person indicating a need for replacing all the ductwork in the house....if you were going with a forced air system then that is absolutely true because the Geo system will not heat the air that goes through the air handler to the same high temp as an oil/gas or wood burner would do and as a result it must move a lot more air. Part of my house was heated with an Air to Air heat pump so the ducting was large.  The rest of the house required significant retrofitting. Closed loop Ground Source Heatpumps are, in my mind far more environmentally friendly that open loop (unless the water is returned to the aquifier...not all are).  The closed loop system must be designed for the load they will be required to support...too big and you have pumping losses and extra trenching and material costs...too small and it wont keep up when you need it more.  The soil make-up is also very important as is the difficulty of digging (horizontal) or drilling (vertical).  Anyone considering Geo should invest in tightening up their home's along the same lines as putting in a solar want to be as efficient as possible to avoid wasting money and energy.  Next is an energy audit to very carefully calculate the energy loss and energy gain of every room in the house which is then translated into the system needed to support those requirements.  Again - now is the time to upgrade the windows, doors, wrap the house in a new layer of insulation and quality siding and double the attic insulation.  If the Geo salesperson does not get out their measuring tape for each window, check insulation levels, look into crawl spaces etc then they are going to size your system based on rule thumb for the size, age and style of home.  In other words you are about to roll the dice on whether your operating costs will be high or low (on top of the premium the system will cost over other options). If you are doing a retrofit I personally cannot see a geo system paying off unless the house already has both hydronic radiant heating in the floors as well as all the related pumps, pipes and controls - AND - ducting with an airhandler for the summer AC.  Without those I would go with other solutions.    The downside of a Geo system, besides its cost, is that the forced air systems make the house feel drafty.  On the up side they tend not to dry out the house the way a burner does. The ideal Geo system is one that uses hydronics.  My house has three parts to it that are laid out in such a way that it is impractical to duct them all together on one or two air handlers....I have three.  These air handlers use radiators to transfer heat (or cool) to the air and to the living areas.  The Geo unit heats (or cools) a large tank of water that is then looped through the three air handlers each with their own circulation pump.  We are hoping to renovate in the next two years and will be installing hydronic radiant heat in the floors as well as ducting positioned for optimum AC.  Our Geo system is most efficient when heating the building through radiant heat for the winter and using forced air when cooling in the summer.  I am a big fan of Ground source heat pumps but like you I have found that every installer will tell you something different and once you understand what really needs to be done you realize just how hard it is to find an installer who is willing to do all the engineering work required to install the optimum solution that will perform and last.

8/24/2019 11:25:36 PM

I have heated my house with an open loop geothermal system since the mid 1980's and I have never encountered a situation where it could not keep the house warm. Also the water from my well is hard and untreated. I live in southeastern Michigan. Maybe I am just lucky.

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