Homeowners Cut Costs With Hybrid Geothermal System
August 1, 2011
MASON NECK, Va. - Perched on the banks of the Occoquan River is a unique house that was just retrofitted with a remarkable HVAC system. The approximately 7,500-square-foot house, with its wall of windows overlooking the scenic river, started out as a small cottage in the 1970s and was then supersized in the early 1990s. As part of this expansion, four high-efficiency propane furnaces and four air conditioning units were installed to heat and cool the newly enlarged space, but after 19 years, it was time to replace the systems with new equipment.
Dave Kyle, general manager, Trademasters Service Corp., Newington, Va., installed those original systems and maintained them over the years, and he relished the opportunity to suggest something different for the homeowners. “The equipment was at the end of its life cycle, and I told the homeowners they should consider a geothermal system, which is what I have in my house. I told them about the generous tax credits available for geothermal, and they did the research and said they absolutely wanted to go that route.”
SAVING ENERGY TOP CONCERNGeothermal wasn’t always on the homeowners’ radar, as they briefly considered replacing their existing high-efficiency propane furnaces and air conditioners with similar equipment. However, the rising cost of propane - combined with the federal tax credits - prompted their interest in higher efficiency systems.
“Saving energy was the homeowners’ first concern, because their propane bills were running about $1,300/month,” said Kyle. “With the lower energy costs and tax credits for geothermal systems, we figured out that they would recover all their costs in seven or eight years. If we replaced the system with conventional equipment, the return on investment would be much longer, because the original equipment was already high efficiency, so we wouldn’t gain much in terms of energy savings.”
The homeowners also liked the idea that since there is no outdoor equipment, the geothermal systems would be much quieter than conventional air conditioners. In addition, they wanted a “greener” system, and they wanted to stay somewhat independent if the power went out during extreme weather. For that reason, Kyle proposed installing a hybrid system that would pair high-efficiency propane furnaces with geothermal systems.
“I argued for the propane furnaces, because the infrastructure for this equipment was already in place, and they can act as a back-up in case there is extremely cold weather or the electricity goes out,” said Kyle. “If there is a loss of power, the propane will run the generator (which is not powerful enough to run the geothermal systems) and the furnaces; otherwise, the homeowners will rarely have to use them.”
Kyle ended up installing four split system geothermal heat pumps from Carrier - three 3-ton units and one 4-ton unit - as well as four Carrier high-efficiency propane furnaces - three 60,000 Btu units and one 80,000 Btu unit. Desuperheaters were added to several of the geothermal heat pumps in order to provide domestic hot water for two of the home’s three hot water tanks. The kitchen, bedrooms, and laundry all receive hot water from the geothermal systems, while the master bathroom has its own high recovery propane water heater.
For IAQ needs, the homeowners chose to have Kyle install steam humidifiers from Aprilaire, air purification units from AtmosAir, and pleated filters. The web-based Schlage LiNK system operates the home’s 10 zones and also automates the door locks, lighting, and security.
“The homeowners were tired of running around, trying to program all the thermostats in the house,” said Kyle. “With the LiNK system, they can just use their smartphone, laptop, or iPad and go to the website and adjust their lighting, temperature control, and door locks. They can also see what’s going on inside their house through the use of web-enabled cameras.”
NO HARM DONEWhile the homeowners were interested in geothermal technology, they did not want their yard torn up in the process of installing the loop fields. To overcome those concerns, a horizontal directional drill was used to install the piping over the expansive lot, which resulted in minimal disruption to the existing landscape.
“Directional drills are just amazing,” said Kyle. “In this case, we had to run a large portion of the geothermal piping into a forest full of 100-year-old trees. We didn’t want to cut the roots or hurt the trees, and we didn’t have to worry about it with the directional drill.”
To that end, the operator used the horizontal directional drill to make a 3-inch hole in the ground that went down about 15 feet into the ground, thus missing most tree roots. If he encountered an obstruction, such as a boulder, he could maneuver the drill up, down, left or right in order to work around the obstacle.
“The drill rig operator basically shot the drill under the yard, the tennis courts, and the driveway, and out into the woods. The drill bit popped up out of the ground, we tied our piping onto it, pulled it back, stepped on the dirt to cover the hole, and we were done,” explained Kyle. “From the point where the directional drill rig was located, the operator would just move the drill 2 to 3 degrees at a time, so the loop piping ended up looking like spokes going out into the forest.”
There was almost no destruction, except for a small trench that had to be dug in order pull the pipe to the house, and the homeowners were very happy that their landscaping remained virtually unscathed. They are also happy with their propane bills, which have almost disappeared since the new systems were installed.
“A month after the system was up and running, the propane company didn’t even bother to fill the tanks, because so little had been used,” said Kyle. “At the end of the second month, only 85 gallons of propane were needed, which is a significant decrease. With our new systems, we basically murdered their propane bill.”
And the homeowners are perfectly comfortable being accomplices to this “crime.”
Publication date: 08/01/2011