Tuesday, August 3, 2010

Zero in on Geothermal HVAC in Virginia



In a typical home, heating and cooling represents 56% of energy usage, the largest piece of the energy consumption pie. To strive for a zero energy home, it is logical to try to drive this heating and cooling load down as low as possible. Although we initially considered using solar thermal radiant heating, we soon abandoned this idea in favor of a geothermal heat pump in combination with solar PV. Solar PV is more "plug and play" than solar thermal, and when combined with geothermal, serves as one low energy solution to both heating and cooling needs, both of which are high demands in the temperate Virginia climate. A ground source geothermal heat pump uses the relatively constant temperature of the ground six feet below the surface, which in Virginia is estimated to be approximately 60 degrees, to heat or cool the home. An antifreeze solution is piped through loops in the ground where, depending on the season, heat is either absorbed and used to heat the home, or the unwanted heat from the home is expelled. As in a conventional heat pump, a compressor and an air handler are used to condense and distribute the heat exchange. A geothermal heat pump does not produce heat, but rather it extracts and moves heat. Where the most efficient gas furnace may approach 97% efficiency, a geothermal heat pump may approach 400% efficiency, in effect, extracting 4 units of heat energy for each unit of energy expended. Research suggests that a geothermal heat pump may result in energy savings of 69% over gas heat and 40% over air to air heat pump heat. Jim Satterfield of HVAC by JM LLC worked closely with our builder to assess our projected heating and cooling loads and recommended a 4 ton Comfort-Aire GeoMax2 split unit connected to 3200 feet of buried loop. The GeoMax2 is a rebranded Climatemaster Tranquility 27 Series, which has an EER rating of 16.6/23.7 and COP rating of 3.7/4.2, some of the highest ratings available. In comparison, Energy Star requirements for geothermal ground source heat pumps are 14.1 EER and 3.3 COP. The two stage compressor and variable speed fan coil contribute to the heightened efficiency while its reliance on R410-A refrigerant protects the ozone layer. The GeoMax2 includes a desuperheater, which uses excess heat to pre-heat your hot water, a nice added benefit. This a split unit, which means that the refrigerant/ compressor unit is seperated from the air handler unit, allowing them to more easily fit in the safety of the conditioned crawl space. The refrigerant/compressor unit is a small gray box about the size of a small bedside table. Once again, great things come in small packages!



The air handler is the same type of blower/ducting
system you have on your furnace.









But then lets not forget that buried loop I mentioned earlier. This involves 3200 feet of 3/4 inch high density polyethelene pipe buried in two 400 foot runs of trenches dug six feet deep and placed 10 feet apart. Suffice it to say that pretty much snaked over every available inch of our front, back and side yards. It looked like the mole from H_ll attacked our lot.


And in this case it was a big bright orange one!

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