Geothermal Misconceptions

By in , , ,
Geothermal Misconceptions
Geothermal Misconceptions

Geothermal heating and cooling is probably the most widely misunderstood concepts in HVAC-R today.  The technology has been around for a lot longer than most people think. The first documents systems were pioneered nearly 80 years ago. We have serviced and replaced systems that were installed 30 years ago in residential applications. Geothermal heat pumps, or ground source heat pumps as they are properly called, are really a specific subset of the more general category called water source heat pumps. Now, the critics may jump out of their seat with fist raised in kerfuffle at me saying that. And their concern hmay have some merit.  Some folks have dabbled in what is called a DX, or direct exchange, ground source heat pump the does away with the “water” part but accomplishes the same task. These systems promise even greater efficiency than “water” based geothermal systems as they remove a heat transfer step. And, they do indeed, while they work. These systems have proven problematic in the real world and most, if not all, get torn up or abandon in a few short years. But we digress.

Misconception 1: “How do you hot water water with cold earth?”

When we start talking about geothermal with most uninitiated clients they often assume that a geothermal heat pump works like a geothermal power plant. A geothermal power plant typically makes use of extremely high temperatures found near subsurface magma chambers that boil liquid water that is pumped down into the earth. That boiled water, now steam, is used to power steam turbines, heat buildings, or even cook food. This is not at all what is done with a geothermal heat pump.  With a ground source heat pump we don’t need very warm earth. In fact, by human standards we often use quite cold earth.  And this is a concept important for all heat pumps: Warm is a human concept, heat is a quantifiable amount of energy. Link to this post about Heat vs. Hot for more detail. 

A ground source heat pump takes heat from the ground through the act of boiling and condensing refrigerant and in many cases freezing and thawing water. “Water” (and I keep putting it in quotes because most systems in the world are closed-loop and recirculate some sort of anti-freeze solution rather than pure water) is pumped from the heat pump itself down into the ground where in winter it is heated up every so slightly, often only 5 degrees F, and then brought back into the heat pump where it removes that 5 degrees of temperature change (heat) and pumps it into the building. In the cooling season, the opposite happens. The heat pump stuffs some 5 degrees of heat into the “water” and it gets pumped through the pipes in the ground where it cools off and returns to the heat pump for more fun. 

The advantage, and source of the high-efficiency ratings, is that the soil stays a relatively consistent temperature year round. Here in New England, our ground temperature below 15 feet stays a comfortable 48-50F all year round. An air source heat pump like a Mitsubishi, Daikin, or Fujitsu has to take its heat from the outdoor air. Here in New England, we can easily see -10F in the dark days of winter. The colder the “source”, be it air or water, the more difficult it is to extract heat from it. It’s not that -10F air has no heat in it, it has quite a lot still.

Ground Loops
Courtesy EPA.GOV

But, it’s rather difficult to capture and use it. A ground source heat pump system can be engineered to control the source temperature (ground temperature) to a much more manageable level and reduce what is called the lift, or the difference between source and room temperatures.  Both machines work the same way fundamentally, but they are laid out quite differently. 

Misconception 2: “It’s too cold ’round here for them geo-thermal systems!”

We hear this one a lot. And this is a hang-over from air source heat pumps which truly did suffer this problem until very recently.  There is likely a lot of fuel companies also trying to protect their precious markets with false and misleading marketing as well. The reality is that geothermal heat pumps don’t care how cold it is outside. An undersize oil furnace can no better heat a house than an undersized heat pump. 

Canada Geothermal
Courtesy Natural Resources Canadaized

The Canadian government is actually a proponent of geothermal heat pumps.  If that isn’t an endorsement for the low-temperature capability of geothermal heat pumps, I don’t know what is. 


Misconception 3: “Geothermal, that too expensive. It never pays for itself”

While few answers are true for every situation, it’s certainly not the case that geothermal is “too expensive” in every situation either.  It won’t be the right choice for everybody, granted. But for many, it is a compelling solution when the analysis is done properly.  The biggest cost difference between a typical HVAC system and a geothermal system is the ground connection, or well(s). But, tax credits and other rebates and incentives typically mitigate this cost. All the indoor equipment, when compared apples-to-apples, costs competitive with conventional equipment. If you compare a geothermal water-to-air heat pump with a 20SEER cooling efficiency to a 13 SEER contractor model air conditioner and a single stage furnace, of course, the price will be a bit different. But when you compare a 20 SEER a/c condenser and at least a 2-stage furnace you will see an entirely different scenario.  Even still, use our fuel cost comparison tool to evaluate the difference heating with propane for example, with a geothermal system. You can see even with a high-efficiency gas furnace, a geothermal system will cost 1/3 as much per year as a propane furnace. For a generic 2000 square foot home, that is probably a savings of  $2000 per year ($1/sqft).  Even for a modest size house, $2000 a year in your pocket for the next 20-30 years sounds pretty appetizing me. 

If you are building new, this is the ideal case for geothermal and pretty much a no-brainer unless you have natural gas available. If you would like us to do the math for your specific situation, we would be glad to help. Please fill out the form below to get in touch.

(0 votes. Average 0 of 5)