February 1, 2017
Geothermal heat pumps grow popular in Fauquier
A geothermal system uses an underground heat exchanger to withdraw heat from the soil and rock. To cool the building in summer, it transfers heat to the ground.
By Warren Darrell
Old Bust Head Brewing at Vint Hill installed geothermal refrigeration units to keep kegs cold.
The Airlie Pavilion has a geothermal heating/cooling system.
Thanks to its geothermal system, efficient lighting and advanced controls, the four-story addition at Fauquier High consumes about one-third less energy per square foot than older sections of the school.
A contractor installs the heat exchanger under parking lots at FHS — a cluster of 160 boreholes, 550 feet deep.
Some Fauquier businesses and homeowners have minimized their energy costs by installing geothermal heat pumps (GHP) rather than conventional heating and air conditioning systems. And, some local businesses profit by providing the systems.
A geothermal heat pump, also called a ground-source heat pump, is similar to a conventional air‑source unit, which moves heat between a building and the outdoor air. A GHP, however, moves heat between the building and the ground.
A GHP is more energy-efficient than an air-source system. A geothermal unit consumes less energy while providing the same amount of heating and cooling, thereby resulting in lower costs for electricity and fuel.
Why is a GHP system more efficient? In Fauquier County, below depths of about 10 feet, the ground temperature is roughly 55 to 60 degrees Fahrenheit year around. During winter, an air-source system works hard to withdraw heat from, say 35-degree air. Meanwhile, a GHP does not need to work as hard to withdraw heat from relatively warm underground soil, rock or water.
During summer, an air‑source system works hard to reject heat into 85-degree air, while a GHP does not labor as much to reject heat into the cool underground “heat sink.” Therefore, a GHP compressor consumes less electricity than an air-source compressor.
The geo-heat exchanger
The unique significant component of the GHP system is the underground geo-heat exchanger.
For a single-family home with a large enough lot, the heat exchanger usually consists of a few hundred feet of flexible piping, buried 4 to 8 feet deep over a wide area. For a larger commercial building, and where ground space is limited, the heat exchanger consists of hundreds of feet of piping buried within vertical boreholes, each of which may be 6 to 8 inches in diameter and hundreds of feet deep.
Water circulates within the piping, withdrawing heat from soil, rock and/or water during winter and rejecting heat during summer. The water then circulates to and exchanges heat with the indoor heat pump(s), which condition the air within the building. Most systems are “closed-loop,” meaning the water stays in the piping. No water or any other material is withdrawn from or released to the earth.
Geothermal for a Fauquier home, school and business
When his propane heat and electric air conditioning system needed replacement, the owner of a 4,500-square-foot home in a hilly, wooded area of central Fauquier chose a geothermal system. It includes two vertical boreholes, each about 550 feet deep, a heat pump serving the upstairs and a heat pump serving the downstairs.
The homeowner cites two benefits – energy cost savings and aesthetics. The electricity consumed by the GHP system costs about the same per year as the preceding system, but there is no cost for propane – an energy cost savings of about $3,000 annually. The GHP does not need a noisy outdoor condensing unit, so the patio is now quieter and more inviting.
The rebuilding of Fauquier High School, completed in 2014, included using a GHP system to serve the four-story addition and the renovated areas of older buildings. The system circulates water through 160 boreholes, each about 550 deep each. The water then circulates to indoor heat pumps that serve classrooms and other spaces.
Fauquier County Public Schools found that the energy consumed per square foot of building served by the GHP system is about two-thirds that of the non-renovated portions of FHS. Some of the energy savings resulted from new efficient lighting, passive solar heating and automatic controls. The energy cost savings averages about 50 cents per square foot annually, which totals about $75,000. In addition, the GHP system has required less maintenance than a conventional system.
The owners of Old Bust Head Brewery at Vint Hill are committed to environmental sustainability, which includes energy efficiency. Their GHP system includes 18 boreholes, 500 feet deep each, 12 indoor heat pumps and refrigeration units. It serves the brewing process and product storage as well as heating and cooling the taproom and business offices.
By comparing his energy costs with those of similar breweries, managing partner Ike Broaddus estimates his GHP system uses about 20 to 30 percent less energy than a conventional system would. Recovering rejected heat for water heating never worked as intended, but otherwise, the GHP system has been largely trouble-free since installation three years ago.
Other Fauquier buildings that use GHP include the lower building of Old Town Athletic Club and the Airlie Pavilion.
Advantages and disadvantages
GHP systems reduce ongoing energy expenses, but they cost more to construct than other HVAC systems. That results from the cost of the underground geo-heat exchanger, although that expense is partially offset because a boiler or furnace is not needed. Construction of the heat exchanger disturbs the ground and requires erosion control, but the area can be fully restored to its former use.
All GHP components are either permanently underground or indoors, resulting greater equipment longevity and less noise — advantages particularly for historic buildings, wineries and homeowners.
For construction of a vertical heat exchanger, the Virginia Department of Health may require measures to protect groundwater. Borehole construction might temporarily and locally disturb nearby groundwater, just as drilling a conventional well would. GHP construction and operation releases no contaminants and does no long-term damage to or depletion of valuable groundwater.
Since a GHP uses less electricity than a conventional system, it helps reduce demand for natural gas, for mining of coal and nuclear fuel and for storage of coal ash and nuclear waste. Less electricity consumption also results in lower emissions of particulates, mercury, acid-forming chemicals and greenhouse gases into our atmosphere.
Fauquier geothermal contractors
Several contractors in Fauquier County provide GHP systems.
Mark Walker, sales manager of McCrea Heating and Air Conditioning in New Baltimore, says the company installs 20 to 50 systems a year, mostly in relatively high-cost homes.
Mr. Walker recommends GHP for energy cost savings, low maintenance and equipment longevity. But, he acknowledges that the higher first cost, expiration of tax incentives and the land area required for the heat exchanger limit the number of customers who chose GHP.
Green Hill Geothermal, also of New Baltimore, provides about 50 residential and commercial systems per year. Tom Drunagle of Green Hill estimates the initial cost for GHP averages about 30 percent higher than a conventional high-efficiency system. Mr. Drunagle cites the advantages as lower energy costs, longer equipment life, and better aesthetics.
If your HVAC system remains in good condition, it probably would not be cost-effective to replace it with a GHP system.
However, for new construction or replacement of obsolete HVAC equipment, a GHP system may be the best choice. For a large or complex system, you should consult an architect or professional engineer with GHP experience, although a reputable experienced contractor can adequately advise most homeowners.
Do your research by considering information available from the International Ground Source Heat Pump Association (http://www.igshpa.okstate.edu), contractors, manufacturers of ground source heat pumps and the Energy Star program of the U.S. Department of Energy. Design, construction cost, and energy cost savings vary; so consider the specifics of your project. The below-ground heat exchanger requires specialized expertise, so choose designers and contractors with good track records.
> Disclaimer: This article does not recommend in favor of or against any product, business or other organization. Each purchaser should exercise diligence.
A professional engineer and Warrenton resident, the writer has 35 years of experience in the HVAC and construction industries. He retired in 2015 as Fauquier County Public Schools’ construction manager. Mr. Darrel oversaw the Fauquier High School renovation and construction project.
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