Geothermal Systems and Net-zero Design
New York Residential Development Taps into Geothermal’s Benefits
After completing a historic geothermal project in 2009 for a net-zero residential development in New York, Lloyd Hamilton was ready for a new challenge. That’s exactly what he got when Anthony Aebi, president, Greenhill Contracting Inc., Rhinebeck, New York, asked him to devise a geothermal solution to heat and cool nine net-zero-ready homes in nearby Mountain Vista, New York.
“When I worked with Anthony in 2009, I was thrilled to be his HVAC and building energy consultant,” said Hamilton, a certified geothermal designer and president of Verdae LLC. “We were making history. The original net-zero development was called Green Acres. It consisted of 25 high-end homes in New Paltz, New York, each incorporating insulated concrete form (ICF) construction, solar panels, and a WaterFurnace Intl. Inc. Envision geothermal system. The selling point for these homes was tremendous comfort and indoor quality, plus an annual heating and cooling energy cost that came to zero. In fact, most of the homes earned money by selling electricity back to the utility.
“Now, after the recession, Anthony called me about a cluster development called The Preserve. He wanted these nine homes to also adhere to the zero-energy concept, but cost 20 percent less. That meant finding a way to reduce overall costs.”
For affordability, Aebi located The Preserve development in the Mountain Vista area, where land costs less. The remote location also meant municipal water was not available. So, Abei asked Hamilton if each home’s well could do double duty: supply domestic water and serve as a closed-loop heat exchanger.
From the builder’s viewpoint, Abei noted 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 request put Hamilton in a different situation from the 2009 project. “Before, all the homes in Green Acres were on the municipal water supply. That meant we had to bore holes averaging 400-feet deep in dense rock for a dedicated closed-loop, vertical heat-exchange well. Drilling through 400-500 feet of rock just for the water-source loop is expensive.
“Abei figured using one well for both domestic water and a heat exchange well would cut down on drilling costs,” said Hamilton. “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 8-inch well, rather than a 6-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 3-ton capacity. There was no need to plug a water heater into the program, because the electricity generated by each home’s solar panels would power a stand-alone electric water heater.
Hamilton selected a vertical-loop type with one u-bend with an average loop depth from the well to the house of 8 feet. After inputting the dense soil type and the minimum and maximum loop temperatures, the program determined the depth of the bore.
“We came up with an average 400-foot well depth with 100 feet of pipe to the house,” said Abei. “Doubling those numbers comes to between 875 and 1200 feet of polyethylene pipe in each loop.”
Compared to other closed-loop water-source installations, that length is short. Hamilton could get away with the short length because homes in The Preserve have an air-tight building envelope and high-R-value ICF construction, which substantially reduces the heating and cooling load.
“I actually see my job as much as a commissioning agent for whole-home efficiency,” said Hamilton. “As defined by ASHRAE, that role involves figuring out the owner’s interests and helping him or her achieve such goals. I understand how the house functions. The shell needs to work properly; the indoor environment needs to be easy to control; and the IAQ, comfort, and durability of the building need to be solid. All of these factors reduce the load and, consequently, the first cost of the geothermal system.”
As a result of the load reduction, Hamilton notes he could select the smaller, 3-ton WaterFurnace 7 Series model. “New York has incentives for builders who build Energy Star-certified homes. Talking with the Energy Star program managers at the New York level, they agreed these homes could meet the Energy Star Home designation by running the 7 Series at a speed that meets the Manual J load calculation. Typically, that turned out to be speed six.
“The WaterFurnace 7 Series is designed to fit in so many situations,” he continued. “It has 14 stages of heating and 12 stages of cooling. So, for example, it can run at 60 percent of capacity or less and meet the cooling load. The neat thing is, the unit can run at any speed down to one. You can have it running at very low speed at very high efficiency.”
In this case, the speed reduction achieved an efficiency that is “far beyond the Energy Star requirement,” said Pasquale Strocchia, who works as a Leadership in Energy and Envirionmental Design (LEED) for Homes Green Rater with the U.S. Green Building Council (USGBC) and as a Home Energy Rater System (HERS) rater for integral building and design in New Paltz.
“The Preserve homes have several energy certifications,” Strocchia noted. “First, they have a HERS index of less than five. Anything less than 15 is considered net-zero capable. The HERS index scale goes from 0-100. A zero is, of course, a net-zero-energy home.
“All of Anthony’s homes are less than seven. The minimum HERS index for an Energy Star home is about 75. So, all his homes easily meet the Energy Star requirement,” added Strocchia. “In my experience, WaterFurnace has always been right in front in terms of the prevalence of units. The feedback I receive from homeowners with existing systems is generally very positive.”
Chrissy and Al Roth, who moved into The Preserve on Oct. 21, 2013, have positive feelings. “We knew Anthony had built the Green Acres community in our area,” said Chrissy Roth. “But, it was out of our means at the time. We lived in a condominium with a boiler and an air conditioning system that needed a few window air conditioners, too. It was highly inefficient. Making the move to an environmentally designed home was what we wanted to do.
“Boy, did it pay off. Even in the worst of the 2014 winter, our January energy bill was just $100. And that was keeping our 2,350-square-foot home at 72°F, 24 hours a day. When my brother and sister visited us, they said it was remarkable to go into every room and have the exact same temperature — downstairs, upstairs, in our bedroom, our bathroom, up in the attic — everything was the same. The WaterFurnace system along with the ICF walls and 18- to 21-inch insulation in the ceiling makes a huge difference.”
Lloyd Hamilton is pleased to be part of another successful Abei net-zero project. “For The Preserve development, the loop is unique. We were able to piggyback the closed loop inside the water well. That saved on drilling costs and site disruption.”
“With the loop being immersed directly in well water, we get high thermal efficiency that takes full advantage of the 7 Series variable-speed capabilities. That is important because we’re in a heating-dominated climate. And, it’s an environmentally friendly solution, too, because we can just use plain water in the loop instead of glycol. The well water doesn’t freeze. It’s a win-win-win that’s worked really well for everybody.”
Information courtesy of Waterfurnace Intl. Inc. For more information, visit www.waterfurnace.com.
Publication date: 4/6/2015