In the past year, we have had an onslaught of inquiries about Geothermal (also known as Geo-Exchange) HVAC. With the availability of a 30% Federal Tax Rebate on top of local and state rebates, it is now economically viable to become “green” with your heating and cooling system. You can even finance the whole project while you wait for your rebates!
Essentially, Geo-exchange is just that, the exchange or extraction of solar energy stored in the earth. The sun’s energy is soaked up by the earth year-round and stored below the initial frost layer. Just 5 feet below the surface, the soil remains a constant 50-55 degrees F year-round. A geothermal or geo-exchange system circulates water with antifreeze through a closed ground loop piping system to capture this energy and return it to a “ground source heat pump” for compression and uses that heat to meet the demand in your building or home. The reverse process moves the heat from your home to the earth to create cooling. Unlike fossil fuel and air-to-air heat pumps, a ground source heat pump can produce 5 times the amount of energy that is consumed with virtually no carbon footprint. A typical fossil fuel furnace can produce only 80% of the energy it consumes in the form of heat and does this while polluting the atmosphere.
Wait a second. Did you say heat pump? Those things don’t work when it gets below freezing, right? WRONG. As previously explained, this is not an air-to-air source heat pump. The history of air-to-air heat pumps in the northeast has been that they were unable to produce high enough discharge air temperatures when the outdoor ambient temperature dropped below freezing. However, we aren’t using air as our heat exchange medium anymore, remember! We are using a constant ground temperature of 50-55 degrees F, even when it is freezing outside. So we don’t have the same fluctuations or temperature minimums as an air-to-air heat pump. In fact, we have left over heat which is used in an add-on heat recovery coil called a “de-superheater” which is used to preheat your domestic water heater or for radiant floor heat. You may need back up hot water heating capability in the winter (usually in the form of an electric immersion heating element), but, depending upon the size of your home or building, your primary hot water heating could be satisfied by a de-superheater in the summer. You are simply putting part of the rejected heat in the hot water and the rest back into the ground from whence it came!
There are 4 main types of geothermal heating and cooling. The first type is called “open loop” which pulls water from an open well to be used in your system and then returns it back to the aquifer via a rejection well, a standing column well or a leaching field. We don’t advocate this type of system because of the brackish nature of water and the associated minerals and alloys contained in the earth. This type of system is less expensive, but does not as long of a system life as does a “closed loop” system. It may also cause cross contamination of the aquifers if one of them contains surface pollutants. There are 3 major types of closed loop systems including vertical loops, horizontal loops and pond/lake loops. Essentially, all 3 types use a closed and fused polyethylene piping system with a flow center (or pump) to circulate the heat exchange medium (water with methanol or another antifreeze) through the ground loops and through your ground source heat pump. We advocate vertical loops bored to a depth of about 200 feet with one vertical bore per ton. A vertical system requires the least amount of acreage for the best heat exchange. There is significant cost in drilling the vertical bores and filling them with a thermally conductive grout (called Betonite), but there is better heat transfer and less property and excavation required than horizontal loops, which lie just below the frost line at 5 feet. If you have a pond near your home or building, this can also be used by sinking a system of closed loop “slinkies” to the bottom to use the water and ground temperature below the freezing surface. For a more in-depth discussion of this process and a geothermal installation, please see this October 2009 article in Popular Mechanics. You can also watch the short WaterFurnace video below.
Air Ideal is one of the largest dealers of WaterFurnace ground source heat pumps in the New York metropolitan and suburban area. We are also one of the few accredited installers who have passed WaterFurnace and the International Ground Source Heat Pump Association’s System Design, Pipe Fusion and Accredited Installers training and testing process. (IGSHPA Accredited ID # 20675-0909). We are a design/build contracting and engineering firm that is capable of working seamlessly with your architect via AutoCAD design drawings or on our own for new installations and retrofits. We conduct an energy survey and load analysis of your home or building to make sure that we size systems that meet your requirements while not wasting excess energy or cost. We’ve set up this easy-to-use Geothermal Savings Calculator to help you see how much a geothermal system can save you.
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