Ԫ Build By Design :: Geothermal HVAC (part 3)

Geothermal HVAC—The Best Thing You Can Do For Clients

What is Geothermal Heating and Cooling?

When asked which energy-efficient features he would include in his dream house, without hesitation Gaylord architect Tad Latuszek tells you a geothermal heating and cooling system would be at the top of his list. "If you do one thing, I would say look seriously at geothermal. The savings will be the equivalent of taking two cars off of the road for each year of use. It's kind of a win-win situation for the homeowner." 1

Direct Exchange Geothermal

There are several ways to use the solar energy stored in the ground to heat space. Each of these options provides significant advantages over conventional heating and cooling systems. For a variety of reasons we have come to believe that direct-exchange or DX Geothermal is the most effective solution.

Direct-exchange systems like the EarthLinked® Systems geothermal heat pumps have several distinct advantages over water-based systems. The salient difference in the design is that DX systems use an environmentally-safe, compressed refrigerant as the medium to conduct heat rather than the water and anti-freeze used by GX systems, and therefore need shorter runs of earth field loops. This affords a number of advantages:

Less equipment to install, maintain and run: Because they don't use water as the energy-exchange medium they don't need to pump water through the system, a costly proposition compared to moving a refrigerant. This also eliminates the need for a water pump and heat exchanger.2

Less complex installation and design considerations: Due to their use of refrigerant and the superior heat conductivity of copper vs. plastic piping, installation of the sub-surface ground loops in DX systems is faster and less intrusive. Bore holes need only be about 50 to 100 feet deep, depending on the specific installation, compared to 150 to 300 feet deep for water-based systems. The manifold footprint can be as small as 6 foot square, reducing landscape disturbance in retrofits and minimizing work-around requirements in new installations3. Direct exchange systems also run the refrigerant line directly into the ground, eliminating the heat exchanger. Because this extra heat transfer step is eliminated from the design, the system is more efficient.4

Superior environmental performance: Direct-exchange systems may be more environmentally-friendly as water-based systems need to use some sort of an anti-freeze. Because water-based systems use plastic pipes rather than copper and need two or three times as much line, there is a much greater opportunity for leaks in the system. DX systems, on the other hand, use shorter runs of robust and highly heat-conductive copper tubing filled with an EPA-approved refrigerant.

Sealing performance: DX systems instead use an environmentally-friendly gas in copper pipes that are encased in thermally-enhanced grout. The grout chemistry is designed to increase heat conductivity as much as possible. The final installation is designed to be permanently sealed, although it can be repaired and recharged if needed. So far, however, with installations dating back to 1980, EarthLinked® Technologies has never experienced a field failure of a production earth loop due to corrosion.5

We can find no better way to sum up the advantages to DX geothermal heating and air conditioning than this: "...ground-source heat pumps have been installed for more than 30 years and are recognized as the most efficient heating and cooling systems available today."6 And another view: "Direct exchange geothermal heat pumps are an efficient, sensible form of renewable energy."7

How Does it Work?

Your clients may have the same question; we ask that you direct them to This Section of the web site for an explanation of how Geothermal works.

For your purposes a good place to start is with the understanding that geothermal works the same as your refrigerator with one exception: the heat-exchange coils are located outside, buried in ground at a constant, year-round temperature. In our terminology we call this the earth loop. For a great explanation on the mechanics of refrigeration go to http://www.madsci.org/posts/archives/1997-12/879298079.Eg.r.html.

Moving Energy: All heat pumps use a vapor compression cycle to transport energy in the form of heat from one location to another. In heating mode, the cycle starts as the cold liquid refrigerant within the heat pump passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source (fluid circulated through the earth connection.) The refrigerant evaporates into a gas as heat is absorbed. The gaseous refrigerant then passes through a compressor where it is pressurized, raising its temperature to over 180 degrees Fahrenheit. The hot gas then circulates through the air handler (a refrigerant-to-air heat exchanger) where the heat is removed and sent through the air ducts or radiant piping. (Either way works fine.) When the refrigerant loses the heat it changes back to a liquid. The liquid refrigerant cools as it passes through an expansion valve, and the process begins again.8

So, a geothermal heating and cooling system heats by transferring the solar heat stored in the ground below your client's ground surface to the building's interior space; it cools by working in reverse, transferring heat from the interior space to the ground beneath it. The schematics below provide an excellent visual explanation of the process.

click to enlarge

Geothermal Water Heating

Would it be a good thing to heat water for free? Many residential installations are equipped with desuperheaters to provide domestic hot water when the system is providing air conditioning. The desuperheater is a small auxiliary heat exchanger at the compressor outlet. It transfers excess heat from the compressed gas to a water line that circulates water to the house's hot water tank. The system is running anyway; why not use energy that would otherwise simply be pumped back into the ground?9 In addition we can install a hot water module in most installations that will heat water while providing heat to the space.

In large installations where heavy hot water demand is anticipated it often makes sense to specify a dedicated system solely for water heating. In fact, initial studies imply a COP of as high as 7 in dedicated geothermal water heating systems. We anticipate the payback on light industrial installations to be very fast due to the very high water heating demands some industries experience.

Finally, if your client has a pool (whether residential or institutional) you will find that geothermal heating is extraordinarily effective. Further, a combination photovoltaic / geothermal system makes year-round pool use affordable.

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1 Michael Jones, "Architect: Look at Geothermal", 6/23/2007,
http://www.gaylordheraldtimes.com/articles/2007/06/22/news/top_stories/doc467c31d867142938188206.txt, (9 July 2008)
2 Washington State University, "Energy Solutions Resources," n.d.,
http://www.energyexperts.org/energy_solutions/res_details.cfm?resourceID=2356&category=Heating%2FCooling%2FVentilation&subcategory=Heat%20Pumps%20-%20Ground%20Source§or=All, (11 July 2008)
3 Ibid.
4 Building Science Consulting, "Case Study—Geothermal Heating and Cooling," n.d.,
http://www.buildingscience.com/bsc/designsthatwork/cold/section3/geothermal.htm (9 September 2008)
5 EarthLinked Technologies, "How It Works", n.d.,
http://www.earthlinked.com/residential/how-it-works, (16 July 2008)
6 John Vastyan, "Geothermal's New Twist," 9/14/2007,
https://www.smart-homeowner.com/ME2/dirmod.asp?sid=&nm=&type=Publishing&mod=Publications%3A%3AArticle&mid=8F3A7027421841978F18BE895F87F791&tier=4&id=BDBDFCFCC92B4AE6AC747590DB58B0D3, (11 September, 2008)
7 Russell Boniface, "Geothermal Heat Pumps Provide Sustainable Alternative for Architects," n.d.,
http://www.aia.org/aiarchitect/thisweek08/0222/0222p_heatpump.cfm, (9 July, 2008)
8 Finger Lakes Institute of Hobart and William Smith Colleges, "Geothermal Heating and Cooling," n.d.,
http://fli.hws.edu/pdf/GEOTHERMAL%20HEATING%20AND%20COOLING.pdf, p 39, (11 September 2008)
9 Ibid p1.

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