I sent an email to Jeff Gagnon and Jim Godbout, and asked them five basic questions about ground-source heat pump installations. In this part of the Green Architects’ Lounge podcast, Phil and I take some time to review and compare their answers. We also take a moment to touch on the subject of ozone-depleting refrigerants. Finally, Phil shares a song by the Brooklyn band Here We Go Magic, called “Collectors.” Be sure to check out Parts One and Two of this podcast to learn the basics of ground source heat pump installations and rules of thumb for well depth expectations. Ready to play “Five Questions” with the pros? Then come on down!
Podcast: Ground-Source Heat Pumps, Part 1: The BasicsPodcast: Ground-Source Heat Pumps, Part 2: Rules of ThumbAre Affordable Ground-Source Heat Pumps On the Horizon?Ground-Source Heat Pumps (2010)Ground-Source Heat Pumps (2009)GBA Encyclopedia: Heat Pumps: The BasicsGBA Encyclopedia: Green Heating OptionsGround-Source Heat Pumps Don’t Save EnergyGround-Source Heat Pumps Have Low Operating CostsHeating a Tight, Well-Insulated HouseEquipment Versus EnvelopeIs a Ground-Source Heat Pump a Renewable Energy System?Air-Source or Ground-Source Heat Pump?
1. When is a house a good candidate for a ground-source heat pump system?
Jim: A large home with very good insulating values.
Jeff: A) Under new construction, a home is almost always a good candidate for a geothermal system, especially if the homeowner is financing the construction project. The increased mortgage payments are offset by the savings in fuel. Therefore, it is “cash-flow positive from day one.”
B) In retrofit applications, it is a great candidate when the equipment in the home needs to be upgraded anyway, or if the homeowner is considering installing a cooling system or simply would like to get rid of their dependence on foreign fuel oil.
2. When is it NOT a good candidate?
Jim: Older home, poor insulation, existing high-temperature hydronic system, existing steam system, due to the amount of infrastructure work required.
Jeff: A) Geothermal is not a good candidate under new construction when the lot size is so small that the setback cannot be maintained to septic tanks and the leach field, or if the ledge is extremely far down. Sometimes this is related to a lot of added expense.
B) Geothermal is not a good candidate for a retrofit application when:
• There is not adequate space for ductwork.
• There is not a low-temperature radiant heat distribution system.
• The basement is finished and there is no attic.
3. What’s your preferred way of doing a ground-source heat pump system (e.g., open loop with radiant slab distribution)?
Jim: Closed-loop concentric high-producing well with water to air using ECM technology circulating pumps and fans for most homes, providing heating and air-conditioning with radiant in the baths and kitchen.
Jeff: Our preferred way of doing a ground-source heat pump system is open loop, using either a ducted or radiant heat distribution system.
4. If I called you up out of the blue and said I have a well-insulated 2,500-square-foot three-bedroom house and I’m thinking of going with a ground-source heat pump, how much is that going to cost me?
Jim: $40K to $50K, with an operating cost around $900 annually for heating and air-conditioning. That is figuring in pumping cost.
Jeff: A 2,500-square-foot home would cost approximately $20,000 to $25,000 for air, and about $25,000 to $30,000 for radiant. This would be approximately a 4- to 5-ton geothermal system. The well and pump system would cost approximately an additional $10,000 to $12,000. If you had to drill a well anyway for domestic water, then you would already be spending $6,000 to $7,000 on the well, in which now you could combine the two.
5. What is the thing that is most often overlooked—or rather, what surprises the clients or designers?
Jim: Design of geothermal is not taken very seriously by many installers. More than half of the listed installs in the state of Maine have problems with performance and operating cost due to poor choices. I know; we get the calls.
Many design systems with electric resistance backup heaters, so this means when we most need heating, they are using the most expensive way to heat the home in Maine, at 15 cents a kilowatt.
Our company will only install closed loop systems that require no electric backup. Some of the larger systems we install use peaking condensing boilers, which also help with large hot water demands.
Money should be spent on the building envelope in almost every case that is brought to me asking about retrofitting geothermal to an existing home. There is no sense in heating the outdoors with ground loop systems, especially at 15 cents a kilowatt. Many parts of the country and Canada pay 6 to 8 cents, which makes it much more attractive.
Jeff: We try not to overlook anything! We use a job information sheet so that on each project we have adequate information before we begin a design. However, I would say the bleed or water discharge location may be the most common unknown. This is because we don’t even know if we need bleed until the well is drilled, etc.