Create a community of affordable, efficient and comfortable net-zero homes with the help of the 7 Series WaterFurnace geothermal unit.
“When I first started working with Anthony in 2007, I was thrilled to be his HVAC and building energy consultant,” says Hamilton, a certified geothermal designer. “We were making history. The original net-zero development was called Green Acres. It was designed for 25 high-end homes in New Paltz, New York, each incorporating insulated concrete form (ICF) construction, solar panels and a WaterFurnace Envision geothermal system.“The selling point for these homes was tremendous comfort and indoor air quality, plus an annual heating and cooling energy cost that came to zero.”
The selling point for these homes was tremendous comfort and indoor air quality, plus an annual heating and cooling energy cost that came to zero. In fact, most of the homes made some money by selling electricity back to the utility—and one resident even uses the electricity to charge his electric car.
“Now after the recession, Anthony called me about a cluster development called The Preserve. He wanted these nine homes to also be NZE, but cost about 20 percent less. That meant finding a way to reduce costs overall, including geothermal installation costs, while improving energy efficiency.”
Single well serves dual purpose For affordability, Aebi located The Preserve development in the New Paltz area where land costs less. The remote location also meant municipal water was not available. So Aebi asked Hamilton if each well for each home could do double duty: both to supply domestic water and to serve as a closed-loop heat-exchange well.
From the builder’s viewpoint, Anthony Aebi notes that, “The issue with water-source geothermal is that if anything ever goes wrong with a well, you have to drill a new one. The other issue is that you have to drill a well in the first place. The idea of using only one well was intended to address both these issues.”
“When my brother and sister visited us, they said it was remarkable to go into every room and have the exact same temperature.”The request put Hamilton in a different situation from the 2009 project. “Before, all the homes in Green Acres were on the municipal water supply,” he says. “That meant we had to bore holes averaging 500 feet deep in dense rock for a dedicated closed-loop, vertical heat exchange well. Drilling through 500 feet of rock just for the water-source loop is expensive. Anthony figured using one well for both domestic water and a heat exchange well would cut down on drilling costs,” Hamilton continued. “Plus, it would cut the maintenance costs associated with open-loop wells, which typically involve a source well and an injection well that gets bogged down with mineral deposits from return water disposal.
“I did some research and found the only issue with using one well was getting enough room to make the closed loop fit. So we instructed the driller to bore an eight-inch well, rather than a six-inch well.”Hamilton determined the well depth using GeoLink Design Studio, WaterFurnace’s geothermal design and energy analysis software. He input the load information and the model—in this case, the WaterFurnace 7 Series variable capacity model NV036 with three-ton capacity. Hamilton selected a vertical loop type with one u-bend with an average loop depth of 200’. After inputting the dense rock type and the minimum and maximum loop temperatures, the program determined the depth of the bore.
“We came up with a 400-foot well depth with 100 feet of pipe to the house,” says Aebi. “Doubling those numbers comes to between 875 to 1200 feet of polyethylene pipe in each loop.”
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