Heating and Cooling
Ground-Source Heat Pumps (GSHP) FAQs

1. 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.

2. How does it work?
A few feet beneath the surface, the earth's temperature remains fairly constant-ranging from 45º or so in northern latitudes to about 70ºF in the deep south-year round. GSHP’s takes advantage of this constant temperature to provide extremely efficient heating and cooling.
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.

3. 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 an complement to the desuperheater, you can have your contractor install a drain water heat recovery (DWHR) system. Visit www.mnpower.com/dwhr to find out more about how they work and how to qualify for the $400 rebate.

4.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 provide 100% of a home's heating and cooling needs. Minnesota Power also encourages customers to look at the air source heat pump (ASHP) option, which extracts heat and cooling from the air rather than the ground. At temperatures below 30 degree F. an additional or backup heat source is required to keep the home warm.

5. Do I need a back up 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 and/or drain water heat recovery system).

6. 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.

7. Are heat pumps noisy?
Heat pumps should be no more noisy than high efficient furnaces.  Noise issues can be resolved by installing the heat pump on a pad to cushion vibrations, properly sizing ducts and insulating the plenum.

8. Are GSHP’s 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.

9. How efficient is a GSHP?
GSHPs are one of the most efficient heating and cooling systems available today according to the US Department of Commerce 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 COP’s (co-efficient of performance) and range from 250 – 350%. This compares to fossil fuel equipment of 60 – 95%.

10. 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.

11. 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 piped 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 degrees 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’.

12. 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.

13. 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.

14. Do both the open and closed loop systems have the same efficiency? (top)
The open loop keeps a more constant incoming water temperature (42 to 45 degrees) 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 degrees, to later in the heating season with the ground temperature is approximately 32 degrees.  The efficiency of the ground source heat pump loop field improves the second year as the ground settles around the loops.

15. What is the cost to install a Ground Source Heat Pump?
An estimate for a contractor installed system that includes excavation, piping, heat pump and ductwork can range from $15,000 to over $25,000.  For a radiant floor heating system with tubing, the cost is for installation is usually higher.  Installed cost will vary based on system size, soil type, type of loop field, and add on features.  

16. What is the pay back for a Ground Source Heat Pump?
Simple paybacks can be as low as 5 years and as high as 30 years. 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: www.mnpower.com/calculators (energy saving tools to energy calculators)