A key and unique component of any geothermal / ground sourced heat pump (GSHP) system is the ground or earth loop. Regardless of the loop configuration, its function is the same: to extract solar energy stored in the ground and transfer it to the heat pump where it will be concentrated to provide heat to your house… and, in air conditioning mode, to receive and absorb heat from your house (after being concentrated by the heat pump). Properly designed and installed, it will last for decades – 75 years or more is a reasonable expectation. I like to think of it as a utility ( analogous to your connection to the electrical grid, but for heat exchange) and a fixed asset of your property — it should only need to be installed once as it will last a lifetime. You’ll be making a lifestyle change (to a superior heating & cooling system) when you install a geothermal system.
Ground loops can be either “closed” or “open”. In a closed configuration, water with antifreeze is circulated through the heat pump and a series of pipes, usually high-density polyethylene (HDPE) specially manufactured for geothermal use, which are heat-fused together so there are no joints or fittings exposed to the elements which could deteriorate over time. There are 3 basic types of closed loop, and one open loop. Let’s look at the pros and cons of each type.
An open loop is a well from which water is pumped through the heat pump and then returned to the ground, either to a second – receiver – well or another acceptable receptacle (e.g. stream, river, or pond). The well must be capable of continuously delivering sufficient flow – at least 3 gallons per minute for every ton of heat pump heating capacity, and be free of biological material and low in dissolved solids. Periodically, the heat pump will need to be acid flushed to remove build up of mineral deposits on the walls of its heat exchanger which would otherwise progressively reduce its efficiency. Frequency of acid cleanings will be largely dependent on the concentration of dissolved solids from the well water and may vary from annually to once every 10 years. Open loops can be the least expensive to install (especially if a clean, productive well already exists). Because well water temperature is typically a constant 45-50F year around, the heat pump will operate more efficiently than any type of closed loop, more than offsetting the additional pumping power requirements.
A horizontal loop is often the least expensive type of closed loop to install provided that sufficient unobstructed land with adequate soil conditions is reasonably close to where your heat pump is located. For a 5-ton system (which will handle the heat load of most 2500sf homes), a 100-ft by 100-ft parcel of land without buried obstructions (e.g. gas, electric, and/or sewer/septic lines; tree roots) will usually be sufficient. HDPE pipe is often laid in several interconnecting trenches. The main (header) trench extends from your house and should be at least 4 feet deep and below the frost line. Several branches of pipe extend from the header in trenches at least 6 feet deep. Ideally, the soil is loamy to ensure good compaction and contact with the pipe; moist, even wet, soil will further improve heat conduction. Dry, gravelly soil is not conducive to heat conduction; if these conditions are encountered, sandy or loamy soil will need to be brought in to lay the pipe on and cover it sufficiently before topping it. Obviously, this could add to the loop installation cost. If bedrock exists and cannot be avoided, a horizontal loop may not be the most practical configuration. As the loop extracts or rejects heat from the soil surrounding the buried pipe, the water temperature entering the heat pump from a horizontal loop will vary throughout the year, from a low of 30F in late winter to greater than 70F in late summer. Provided that the heat pump and loop have been sized properly, the system will perform effectively over this range, although the efficiency will vary somewhat. Solar energy striking the ground surface will also penetrate tens of feet into the ground, replenishing the net heat that is withdrawn and moved to your house year after year.
If sufficient land and soil conditions are not available, a vertical loop may be the only closed loop option. Instead of trenches, the branches of the loop are one or more holes at least 15 feet apart, drilled hundreds of feet deep. A u-shaped pipe is inserted in each and connected to the headers extending from the heat pump. Each hole is packed with thermal grout to ensure good heat conduction to and from the surrounding earth. Depending on soil and temperature conditions along the depth of the bore hole and the depth of each hole, 2 to 3 bores may be sufficient for a 2500sf home. Unlike a horizontal loop, solar energy absorbed by the ground will have little effect on the heat stored at depths typical of vertical loops, so the design needs to account for and mitigate the effect of accumulating net heat extraction in heating dominated regions like New York State. For smaller systems like those common for single-family homes, vertical loops are more expensive to install than horizontal loops but equally as effective.
My favorite closed loop configuration is the pond loop, which is similar to a horizontal loop except that the majority of the pipe is placed near the bottom of a pond or lake rather than buried in trenches. The pond loop is often even less expensive to install than a horizontal loop as the only required excavation is to run the header pipes from the heat pump to the pond. As a geek, what I really love about a pond loop is the higher average water temperatures that it delivers to the heat pump during the winter which enables it to operate at higher efficiencies. Liquid water is at its maximum density at 39F, so if the pond is sufficiently deep, the water surrounding the branches of the loop (positioned about a foot above the pond bottom to keep it out of the silt and muck) should never be less than 39F. In addition, soil conditions are largely removed from the equation and water is an excellent conductor of heat to and from the loop. If you’re fortunate enough to have a pond or lake close to your house (and regulations don’t prevent it), a pond loop is the way to go.
Regardless of which type of loop is part of your geothermal / ground sourced heat pump system, it will truly be your own personal utility and a fixed asset of your property for decades. Call us to schedule a free site assessment to determine which is most appropriate for your situation.
Lake Country Geothermal, Inc. services the Finger Lakes and Greater Rochester NY areas, including Albion, Auburn, Avon, Batavia, Bloomfield, Branchport, Brighton, Bristol, Brockport, Caledonia, Canandaigua, Clifton Springs, Clyde, Cohocton, Conesus, Churchville, Dansville, Fairport, Farmington, Gates, Geneseo, Greece, Groveland, Hamlin, Hemlock, Henrietta, Hilton, Honeoye, Honeoye Falls, Ionia, Interlaken, Irondequiot, Kendall, Keuka Park, Leroy, Lima, Livonia, Lodi, Lyons, Macedon, Marion, Macedon, Mendon, Mount Morris, Mumford, Newark, North Rose, Ontario, Ovid, Palmyra, Pavilion, Penfield, Penn Yan, Pittsford, Port Byron, Prattsbugh, Pultneyville, Red Creek, Riga, Rush, Savannah, Scottsville, Seneca Falls, Sodus, Shortsville, Spencerport, Springwater, Victor, Walworth, Wayland, Webster, Weedsport, Williamson, Wolcott, Wyoming.