Frequently Asked Questions
What is Ground Source Heat Pump (GSHP) technology?
Ground Source Heat Pumps (GSHP) are electrically powered systems that tap the stored renewable energy of the greatest solar collector in existence: the earth. These systems use the earth's relatively constant temperature to provide heating, cooling, and hot water for homes and commercial buildings.
How does it work?
A few feet beneath the surface, the earth's temperature remains fairly constant, ranging from 45°F or so in northern latitudes to about 70°F in the deep south year-round. GSHPs take advantage of this constant temperature to provide extremely efficient heating and cooling.
Ground source heat pumps can be categorized as having closed or open loops, and those loops can be installed in three ways: horizontally, vertically, or in a pond/lake. The type chosen depends on the available land areas and the soil and rock type at the installation site. These factors will help determine the most economical choice for installation of the ground loop.
For closed loop systems in winter, a water/antifreeze solution circulating through pipes buried in the ground absorbs heat from the earth and carries it into the home. The GSHP system inside the home uses a heat pump to concentrate the earth's thermal energy and then to transfer it to air circulated through standard ductwork to fill the interior space with warmth. (Hot water GSHPs are also available, which are ideally suited for radiant slab heating). In the summer the process is reversed; heat is extracted from the air in the house and transferred through the heat pump to the ground loop piping.
Open loop GSHP systems operate on the same principle as closed loop systems and can be installed where an adequate supply of suitable water is available and open discharge is feasible.
Can one system provide both space heating and cooling for my home? And what about heating hot water?
Yes. A GSHP can be a combination heating/cooling and hot water heating system. You can change from one mode to another with a simple flick on your indoor thermostat. Using a desuperheater, some GSHPs can save you up to 40% on your water heating bill by preheating the water for the domestic hot water tank. Note: As a complement to the desuperheater, you can have your contractor install a drain water heat recovery (DWHR) system. Visit our DWHR page to find out more about how they work and how to qualify for the $400 rebate.
I have heard that heat pumps do not provide adequate heating during the coldest winter months and can cause discomfort problems in the home.
GSHPs can provide 100% of a home's heating and cooling needs. Your contractor can work with you to design a GSHP heating and cooling system that can take advantage of existing heating systems and/or supplemental electric heating based on your needs and cost considerations.
Do I need a backup heating or cooling system with a GSHP?
No, a properly designed system can provide 100% of your heating needs, 100% of your cooling needs, and up to 40% of water heating needs (if the water heating package includes a desuperheater). You may consider utilizing an existing heating system or supplemental electric based on land area, soil conditions, and cost considerations. Note: Designing a system that is not 100% GSHP will increase operating costs.
How much house space does a GSHP require?
Most of a GSHP system is underground. Inside the house, the heat pump units are about the same size as a traditional heating and cooling unit.
Are heat pumps noisy?
Heat pumps should be no more noisy than high-efficiency furnaces. Noise issues can be resolved by installing the heat pump on a pad to cushion vibrations, properly sizing ducts and insulating the plenum.
Are GSHPs safe?
GSHP systems are safe and protected, with no open flame, flammable fuel or potentially dangerous fuel storage tanks to worry about. With no exposed equipment outdoors, children or pets cannot injure themselves on, or cause damage to, exterior units.
How efficient is a GSHP?
GSHPs are one of the most efficient heating and cooling systems available today according to the US Department of Energy and the Environmental Protection Agency. Heating efficiencies are typically 50% to 70% higher than other heating systems and cooling efficiencies are 20% to 40% higher than available air conditioners. That directly translates into savings for you on your utility bills. Efficiency of GSHPs are related in COPs (co-efficient of performance) and range from 250%–350%. This compares to fossil fuel equipment of 60%–95%.
What are the different types of outdoor loop fields?
Loops can be installed in three basic configurations: horizontal slinkys, vertical bore holes, and pond or lake loop systems.
Tell me more about the horizontal slinkys.
In Northern Minnesota, most closed loops fields are called slinkys (so named for the child's slinky toy). Coiled pipes are installed horizontally, 7' to 8' below grade. Depth of the trench is affected by climate and soil type. At this depth, the earth temperature is a constant 45° to 50° year-round. To make a slinky for each ton of heating, 600 feet of pipe is coiled up to a length of 80 feet. A five-ton system requires an approximate excavated area of 25' x 80'.
How deep is a bore hole for a vertical system?
A bore hole is 150' to 200' deep for one ton of heating. The bore hole is 4" to 5" in diameter. Each bore hole must be a minimum of 10' apart.
What soil types are best?
Soils with moisture provide the best heat transfer. Fine soil is better than a coarse soil for heat transfer. Boring into ledge rock is generally not economically feasible.
Do both the open and closed loop systems have the same efficiency?
The open loop keeps a more constant incoming water temperature (42° to 45°) so the efficiency is also consistent. The closed loop system loses some efficiency from the start of the heating season, when the ground is approximately 55°, to later in the heating season, when the ground temperature is approximately 32°. The efficiency of the ground source heat pump loop field improves in the second year as the ground settles around the loops.
What is the cost to install a Ground Source Heat Pump?
The initial investment for a GSHP system is greater than that of a conventional system. However, when you consider the operating costs of a geothermal heating, cooling, and water heating system, energy savings quickly offset the initial difference in purchase price. An estimate for a contractor installed system that includes excavation, piping, heat pump and ductwork can range from $15,000 to over $25,000. Installed cost will vary based on system size, soil type, type of loop field, and add-on features. Note: You may want to talk to your contractor about ways to lower the initial cost by reducing the size of the loop field and adding supplemental electric heating or utilizing an existing heating system. This will reduce the initial cost but increase your operating costs. Expect to see higher electric bills in the coldest weather. See "Do I need a backup heating or cooling system with a GSHP?" above for more information.
What is the payback for a Ground Source Heat Pump?
GSHPs save money, both in operating costs and maintenance costs. Investments can be recouped in as little as five years. There is a positive cash flow, since the energy savings usually exceeds payment on the system. Savings and paybacks depend greatly on the available fuel type, fuel cost, size of home, and amount of heating and cooling loads. There is a greater savings potential for larger homes (2,000 sq. ft. and above), where natural gas is not available, and when air conditioning is to be installed. To find out more about fuel cost comparisons, visit our Energy Calculators page.
Will I have to add insulation to my home if I install a GSHP system?
GSHP systems will reduce your heating and cooling costs regardless of how well your home is insulated. However, insulating and weatherizing are key factors in gaining the maximum amount of savings from any type of heating and cooling system. Visit our Home Energy Analysis (HEA) page to determine if an HEA is right for you. The HEA will help you identify other ways to save energy in your home.
How long will my GSHP system last?
GSHPs are durable and highly reliable. The GSHP contains fewer mechanical components, and all components are either buried in the ground or located inside the home, which protects them from outside conditions. The underground pipe carries a 50-year warranty.
What about comfort?
A GSHP system moves warm air 90°F–105°F throughout your home or business via standard duct work. An even comfort level is created because the warm air is moved in slightly higher volumes and saturates the building with warmth more evenly. This helps even out hot or cold spots and eliminates the cold air blasts common with fossil fuel furnaces.
Do soil freezing conditions create any problems?
Not if a system is properly designed and installed. The three- to four-foot depths allow the sun to melt the frozen soil during the summer. Adequate length per ton capacity prevents objectionable soil movement.
Will my existing duct work function with this system?
Yes, in most cases. Your dealer or installer will be able to determine duct work requirements and if any modifications are needed.
Will an underground loop affect my lawn or landscape?
No. Research has shown that loops have no adverse effects on grass, trees, or shrubs. Temporary bare areas can be restored with grass seed or sod. Vertical loops require little space and do not damage lawns significantly.
Does Minnesota Power offer any incentives for installing a qualifying GSHP?
Yes, Minnesota Power offers an incentive for installing a qualifying GSHP system in homes located in our service area. The unit must be installed by a product and program trained contractor. Visit our GSHP page for more details on how to qualify for the incentive and to find out more about tax incentives.
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