As the costs of oil, natural gas and electricity to fuel conventional heating and cooling systems rise, homeowners are increasingly installing heat pumps. By extracting warmth and coolness from the outside air or ground, heat pumps can provide greater efficiency and lower cost over the long haul.
Two basic options predominate. In air-to-air designs, a unit outside the house relies on air as a source of heat or a place to dump heat. In ground-based designs, fluid in tubes laid in the ground provides the heat transfer. In each case, a refrigerant travels in pipes from outdoors to an inside unit, and a blower sends the resulting warmed or cooled air through ductwork into various rooms. The systems are often likened to a reversible air conditioner that can stream cool air or exhaust warm air throughout the home. “When the season changes, you just flip a switch and the flow reverses,” says Leo Udee, account manager at Alliant Energy in Madison, Wis.
Even though both systems require electricity, they can attain greater efficiency than conventional designs because instead of consuming fuel to generate warmth or coolness from scratch they exploit heat or cold already present in the outside air or ground. Air-to-air systems are most effective when outdoor air is above 32 to 35 degrees Fahrenheit, however, so they are prevalent in the milder regions of the U.S. A small conventional heater can be added in colder climates, but that drives up cost. Ground-based systems with tubes installed six to eight feet below grade are useful in wider areas because the temperature of the earth does not dip below freezing at that depth, although they generally cost more to install.
Heat pumps have been around since the 1950s and have become more competitive in recent years because “the motors and compressors have gotten more efficient and cost less to operate,” says Randy Scott, vice president of product systems management at Trane in Tyler, Tex. “And the condensers and evaporators can transfer more heat even as they have become smaller.”
Heat pumps still command only a modest proportion of the home heating and air-conditioning market. Even so, both styles are seeing strong growth, especially for retrofits. So many homes were built in the 1970s, 1980s and 1990s, Scott says: “Their systems are nearing the end of their lifetimes.”
Note: This article was originally printed with the title, "Warming and Cooling".
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10 Comments
Add CommentI'm surprised to note that heat pumps are not more widely used than the article implies. I have been using a heat pump in my present house for 17 1/2 years. Prior to that I had one installed about 1979 in a house which I still own in Mobile, AL. As far as I know, everyone in my family is using a heat pump presently especially my Brother-in-law in Young Harris, GA who works for Southern Company. His house is always very comfortable.
Reply | Report Abuse | Link to thisWe built a new underground home in 2002. It has about 3000 sq feet, and is heated and cooled with a ground source heat pump. Our heating/cooling bill averages about $40/month, with no heating or cooling required for 5-6 months per year. The electric bill at previous home was 500/month summer or winter. (2 story 2400 sq ft conventional home with electric heat) New home was designed for energy efficiency, with all florescent lighting, and energy efficient appliances. The cooling pipes were installed during construction, which resulted in minimal expense. I also have a loop into a large pond that helps in the cooling efficiency.
Reply | Report Abuse | Link to thisFrom: Norman Duncan, P.E.
Reply | Report Abuse | Link to thisDate: July 19, 2008
Subject: Working Knowledge "Warming and Cooling" Article August '08
To: Mark Fischetti, Editor
Sir:
Regarding your August 2008, "Warming and Cooling" article, the lower 15 foot interconnect of the vertical loop tubes shown in the illustration at the lower right of page 104 is totally impractical to construct.
How can the interconnection between the two vertical refrigerant-filled tubes be constructed at a depth of 150 to 200 feet?
In general, this article needed a more critical review by experienced experts in the field, e.g. a well drilling contractor and piping engineer.
By the way, heat pumps have been around since the 1840's, look up Dr. John Gorrie.
chuckh: What is your general geographic location and climate? neduncan, Miami, Fla.
Reply | Report Abuse | Link to thisI am in southwest missouri, just north north of Joplin. We have mild to moderate winters, with fairly hot summers last few years. Coldest winter temp about 0, usually 1-2 weeks, rest of winter averages 20-30. About 1 month of hot summer, about 100, rest of summer milder 80-90 highs. We also have high humidity here. My house has more cooling demand than heating demand, I think this is mainly due to generated heat from appliances, cooking, etc.
Reply | Report Abuse | Link to thisI can't find the page 104 you referenced, but we are in construction, and use to have water/oil well drills. This was about 20 years ago, but i think we put in 150' of borehole per ton of heating/cooling. We installed a few heat pump wells, using 1-1/2" poly pipe. We heat fused a 180 u bend on the bottom (we rented a pipe fusion machine), drilled wells 180' deep, 10' apart. We used stainless steel hose clamps ( you must special order ALL stainless, most common clamps have stainless bands with carbon steel screw) and used a hose splice to join the loops about 2 feet under the surface. We were able to fill the bore hole with water, and lower the U-bend poly pipe in the hole. Gradually fill the pipe with water so it would sink ( It floats if empty). After the pipr was in the bore hole, we filled the hole with sand. By filling it with water, the sand doesn't bridge over, and will fall to the bottom of the hole.
after the loops were connected, we flushed them out with a gas powered pump (high volume to remove any dirt), them circulated a 25% antifreeze solution through the loops and heat pump.
Chuckh: We are in Miami Florida and therefore mainly interested in cooling, I want to install a heat pump based on the ground water in our pervious rock. Our 1951 house originally had a surplus heat pump from a WW2 submarine that worked fine until we couldnt repair it. The page number was not on the first page of the article but was on the facing page with the A/C illustrations. It sounds to me like you had a 6 inch diameter bore hole with a 1-1/2 inch poly pipe going down and the same coming up after the u-turn at the bottom. I am thinking about concentric pipes, a steel casing with a PVC supply going down the middle and the return flow coming up the annular space. Norman Duncan 8/29/08
Reply | Report Abuse | Link to thisChuckh: We are in Miami Florida and therefore mainly interested in cooling, I want to install a heat pump based on the ground water in our pervious rock. Our 1951 house originally had a surplus heat pump from a WW2 submarine that worked fine until we couldn’t repair it. The page number was not on the first page of the article but was on the facing page with the A/C illustrations. It sounds to me like you had a 6 inch diameter bore hole with a 1-1/2 inch poly pipe going down and the same coming up after the u-turn at the bottom. I am thinking about concentric pipes, a steel casing with a PVC supply going down the middle and the return flow coming up the annular space. Norman Duncan 8/29/08
Reply | Report Abuse | Link to thisYou are correct on the polypipe and uturn. I think we drilled a 5 3/4 hole. we stopped at 180' because the rock formation got VERY hard there. It was much easier to move over than to drill deeper. In my house, with more cooling demand than heating demand, I had a increase in my loop temperature until I started circulating to a cooling loop in a large pit in the winter. this helps bring down the underground loop temperature in the winter. In our area, steel pipe doesn't last very long unless it is cemented in top to bottom. We have coal seams from 50-200' down that have sulfur in them. that make sulfurous acid which has really sharp teeth on steel pipe.We lost a fresh water well when the casing collapsed on the water pipe and pump. we were able to pull the pump, but never able to get anything back down the hole. In the geothermal wells we used polypipe, which eliminated the chemical reaction problem, and there were no joints to leak or fail. The University of Oklahoma used to have a large amount of information on geothermal heat pumps available to the public. When I built my house, I had a large area to work with, so I put about 2400' of polypipe in horizontally, about 12' deep. I also have about 500' in a large pit, about 20-30' deep. My loop temperatures don't get below 50 degF winter, or above 85 deg F summer.In about Feb I circulate cold water from the pit loop to the underground loop to help remove heat from underground loop for the next summer.
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Reply | Report Abuse | Link to thisThank you so much for this article. I had no idea that you could get <a href="http://www.nri-isd.com/categories/Pumps/">surplus pumps</a> that both warm and cool. This seems like it would be a great pump to have, and hopefully it could save money as well. Thanks again! http://www.nri-isd.com
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