Digging Geothermal

(By: Dana Weeder, AIA LEED AP and Mike Fields)

I really like geothermal energy.

Before I am redressed by scientist friends, I should clarify that there is not much in the way of usable geothermal energy in the Northeast United States.

Direct Geothermal Energy harvesting is probably best known in places like Iceland, where more than half of the nation’s energy needs are met by capturing heat that escapes between the Earth’s tectonic plates. While this has a low environmental impact, there are a limited number of places on the planet which are close enough to tectonic heat sources to make effective use of it. If you are close enough, you run the risk of seeing more of the inner workings of the planet than one might like.

However, the growing geothermal industry in New England is based on what is called Ground Source Heating and Cooling (and I like that too). This type of system exploits the Earth’s ability to insulate, store and dissipate heat, allowing the ground to act as a sort of thermal flywheel.


So, what is a Ground Source Heat Pump (GSHP) system?

While our atmosphere is dynamic, with huge temperature extremes, temperatures several feet below surface of the earth are a relatively stable +/-55 degrees throughout the year. We can use the difference between the ground and the air to control building temperature with heat pumps which amplify the temperature differential through a change of state, similar to what happens in an air conditioner or refrigerator.

No, seriously, what is it?

Basically, you stick a plastic tube into the ground and pump a solution of water and glycol through the tube. The solution is then pumped into a heat pump which will either remove ‘heat’ from the solution (heating cycle) or add ‘heat’ to the solution (cooling cycle). In the summer, the heat pump returns the solution to the ground in a warmer state and is consequently cooled by the earth. In the winter, the heat pump returns the solution to the ground in a cooler state and is consequently warmed by the earth. So it’s a bit counter intuitive, but in a heating cycle, a heat pump can actually pull ‘heat’ out of a 55 degree solution and return the solution to the ground at 35 degrees. That 20 degree differential is borrowed out of the ground and put into the building. And the exact opposite occurs during the cooling cycle.

Why is this so great?

A Ground Source Heat Pump system differs from conventional systems by its ability to transfer heat rather than produce heat. A GSHP system does not heat from fuel, it simply moves existing heat from one place to another. This greatly reduces the building’s carbon footprint and lowers operational costs. So, the idea of borrowing heating/cooling is what makes it great.

Is that it?

No, since the only energy going into the system is electricity, the real promise of GSHP is as a component of on site power generation or more sustainable infrastructure. As electrical power inevitably becomes more efficiently generated and distributed, the savings from the economic and environmental savings will increase with them instead of becoming obsolete. There is no large roof top cooling tower that needs to be replaced every 20 years and no boiler taking up internal space.

But unfortunately, a lack of familiarity with these systems has been keeping clients and contractors wary and costs up. Many will require backup heat, oversize the systems, or avoid them altogether. There is great potential to plug our buildings into the Earth and architects and engineers need to build confidence by collecting and dispersing data on carefully designed systems.

Kathryn and Mike checking Needham's Geothermal Pump

Winter Street Architects recently completed the Needham Public Services Administration Building which has a series of (16) five-hundred foot deep wells located under the parking lot. Heat pumps are distributed throughout the 22,000 sf building which collects available heat to circulate through the building in the winter and discharge heat back into the ground in the summer. The system went on-line this past November and has been running without incident or backup heat through this most recent winter. The building was also designed to be ‘solar-ready’ with a large south facing sloped roof.

Is it right for all buildings?

Not yet. There are many variables in play; from the size of the building to its life expectancy to the thermal conductivity of the ground on which it is built. While the initial costs can still be steep and the return on investment still a bit long, it has to be a balance of economics, sustainable commitment and optimism. We think it will get there.

And we dig it.

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Comments
8 Responses to “Digging Geothermal”
  1. I have a ground source geothermal heat pump at my house (1550 sf), and I love it! Since it is able to extract heat even during the coldest periods, I disconnected the auxiliary heat strips shortly after we moved in (8 years ago). By not having the auxiliary heat connected, I am able to use a programmable timer to control the heat pump (without triggering the energy hungry heat strips). Here in the mountains of Virginia, our highest heating or cooling bill is never over $120/month.
    An added benefit is the quiet around my house – no noisy outside unit!

  2. Vince Hovda says:

    I have an 100 year old 3,500 sq. ft. Virginia home with a huge old duct system. I plan to rip out the old converted oil furnace. I have a big yard and I love this geothermal idea. Will it work for me or is this place too big? Also, I’d like to dig the trenches myself to save money and I am wondering how much savings this would create.

    • danaweeder says:

      You should have little concern regarding the size of the house…all of the GSHP systems we have completed have been in buildings over 20,000 sf. Initially, I would be more concerned with air infiltration in your 100 year old house. Your money is best spent on tightening your house in every possible way and then, and only then, design/install a GSHP system to your now lowered heating/cooling needs. And the additional upfront costs of tightening your home will allow you to downsize the GSHP system.
      Digging your own trenches will also certainly save you money…difficult to say how much without more site conditions knowledge. But I would like to re-iterate, running a GSHP system is by no means free. You need to factor in increased upfront costs and the electricity to run the pumps. But ultimately ROI for these systems are generally in the 5-10 year range based on today’s fuel costs.
      And finally, there is a bit of the wild west mentality in the GSHP world. There is a lot of activity, a lot of potential and a lot of unsubstantiated promises. Find yourself a good consultant/vendor who is willing to return to commission the system, and then return again and again if needed. There are stories of folks who are paying higher electrical cost for their GSHP system than the fuel costs of their previous system. These stories are most definitely the exception, but they are the result of poor design and/or lack of proper commissioning.

  3. Interesting post. Installing a geothermal heating/cooling system can drastically reduce your energy costs and promote a healthy ecosystem. Great post.

  4. phaed says:

    I like this content so much.The determined man finds the way, the other finds an excuse or alibi.Thanks.

  5. Patty says:

    I absolutely loved reading your post about geothermal. My husband and I own a green company here in Georgia. We try to always educate our customers/clients. Thanks for the geo edu! Geothermal Atlanta EcoMech

  6. There are cheaper ways to use less energy, but this way we keep about the same amount of comfort, and I can continue to use my home office, while still reducing our carbon impact (from home energy use) about 46%.

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