[johnmarkos]

I'm starting this thread to explore conservation through the use of heat pumps. According to the EIA, HVAC (heating, ventilation, and cooling) is the biggest use of electricity in homes. Heating is also a big use of natural gas in many homes.

Heat pumps can be used to make heating more efficient. Here's some information from the IEA on heat pumps.

What applications of heat pumps have you observed in homes? In industry? What are concerns or limitations regarding this technology?

[Kingcoal]

Geothermal heatpumps are becoming popular in the Pocono Mountain regions of PA. Standard heatpumps are useless around here because of all the time we spend below freezing. Geothermal heatpumps get around the iceup problem with the heat exchanger in various ways. One way I've seen is to submerge the heat exchanger in well water. A pump keeps fresh water flowing through and the spent water is dumped back into the ground. Well water is about 45 degrees year round which is warm enough to extract heat for the house. As an added bonous, air conditioning is pretty much free in the summer.

The reason for the their popularity in the Poconos is due to the lack of infrastructure, heating options are few. However, electricity is available and relatively cheap (from a nuke plant), so electric heat has been popular for some time.

I think that geothermal heatpumps will become very popular in the future as we run out of oil and gas. These heatpumps are very efficient from a EROEI perspective. For example, electric resistive heat is 100% efficient, but the entire process from the energy used to generate the electricity to your house is probably only about 30-50% efficient. Geothermal heatpumps take advantage of the free energy stored in the earth.

[Tanada]

$this->bbcode_second_pass_quote('johnmarkos', 'I')'m starting this thread to explore conservation through the use of heat pumps. According to the EIA, HVAC (heating, ventilation, and cooling) is the biggest use of electricity in homes. Heating is also a big use of natural gas in many homes.

Heat pumps can be used to make heating more efficient. Here's some information from the IEA on heat pumps.

What applications of heat pumps have you observed in homes? In industry? What are concerns or limitations regarding this technology?

[kyzmiaz]

We live in a 1650 square ft. well insulated total electric ranch home we built in 1990. In 2002 / 2003 our electric bill was $128 per month @ around .11 per KWH. We live in Southern NJ where summers are hot and humid and winters are moderate. We are comfortable in the summer with the thermostat set at 77 degrees due to the geothermal the heat pumps superior humidity removal. Our water source open loop geothermal heat pump (www.floridaheatpumps.com) has a cop of 4 and a EER of somwhere around 20. Our heat pump also has a 'desuperheater'. It makes cheaper winter / free sumer hot water while keeping the compressor cool. In 15 years we had one service call to replace the start capacitor. No maintainence required - just replace air filter. We now also have 9.9 KW solar system. Our total monthly utility cost is now under $20 @ .125 KWH. We love our geothermal heat pump. A disadvantage was its higher initial cost $6000 VS oil with central air $4000 (1990 dollars) and its eventual higher replacement (20 + years lifespan) cost.

[frankthetank]

I've got a well, but i'm think you would need to return that water to the ground somehow...another well??? It would be an awesome to get this "free" energy, but the cost would probably keep me out of the game, atleast for awhile.

[Starvid]

Heat pumps are widely used in Sweden. Mainly in previously oil- or direct electrically heated single homes, but also by industry and in apartment buildings to avoid the central heating monopolies which have increased prices a lot in recent years.

[drew]

I have looked into a ground source heat pump, and don't have the money, yet, to install it. The system I want requires around 400 ft of pipe buried 6 ft deep in our yard. Needless to say this requires an excavator. I have heard it is too cold up here but who knows? 6 feet is under the frost line, so I can't see the problem.

What is a possible problem though is efficiency, and reliability. Most gs pumps use two loops, secondary and primary, with consequent heat losses. There are also two pumps, running continuously, using a fair bit of hydro. A newer type I looked into, from Nova Scotia, uses one loop to minimize thermal losses, but has the (potential) problem of the pump lubricating oil dropping out of suspension in the gas stream. The manufacturer claims that they have overcome this.

In addition, one's ventilation system needs to be large enough to handle the increased volume of less hot, or cool air a heat pump produces. As for installation, a gs pump is a major undertaking. My guess for my home is between 10 and 15 K.

All in all though, gs pumps are an awesome technology, and would be a great investment if done with prudence. Picking the right contractor and manufacturer is crucial, since this application is still nascent.

Drew

[dbarberic]

Does anyone know if you can retrofit an existing built house with Geothermal?

I did a quick search on the web and it seems like you can, but I would like to know if anyone has first hand experience in doing it or knows of someone who did?

[donshan]

Over the years I have owned two houses with heat pumps, including my present one. Both used the outside air handlers to extract heat in winter and dump heat during air conditioning to the outdoor air. The heating phase is simply a more robust freon compressor running an A/C backwards cooling the outdoors and warming the house. The A/C summer load needs to be considered in the design to size the unit for both the cooling and heating season.

This principle is the same if you use an underground piping or water system for the heat source/sink. In a few locations water is available in sufficient amounts to make these type of systems the most efficient heat pumps possible. However, very few locations qualify for sufficient quantity of water at acceptable prices. I would call several of your local heating/cooling contractors to see if your area has successful systems already. If so contact the owners. If there are not any already I would be VERY cautious about being the first.

My experience in giving up on the heat pump in this house will illustrate some of the problems to consider. Once you understand that a heat pump is a big air conditioner running backwards you can see the the outside heat source/sink is the key. In my system ( and most heat pumps) this was an outdoor unit with a heat exchanger/fan system. The freon is compressed and becomes a hot liquid. It then goes through the indoor fan system to heat the house. After the heat is removed the freon then goes to the outdoor unit and expands back to a gas cooling the outside air passing over the outdoor unit. The coils literally get colder than the outdoor air, and can freeze water out of the air causing the coils to frost up. This blocks the air flow. The heat pump design anticipates this and when it detects frost, the heat pump automatically reverses for about 20 minutes or so, cooling the house and heating the outdoor coils to defrost the system with the water going out on the ground somewhere ( a small ice puddle forms on the ground!). Obviously this defrost cycle wastes heat from the house. What the manufacturers don't tell you is if your outdoor air humidity is near the dew point, frost forms often and the heat pump will be alternating between heating the house and cooling it all day long on a foggy cold day. This was my problem. I was not sure there was ANY efficiency advantage on foggy days about 32F. The heat pump was just wearing itself out.

If you could extract heat from a flowing water stream at say 50F then all is well. The outdoor exchanger stays at 50F and frost never forms. However if you place the piping just underground, then it is possible to freeze the earth surrounding the piping and eventually you can't get any more heat. So these underground systems work best with lots of ground water that moves. An experienced contractor is an absolute MUST for such underground loop systems.

Further, the economics of air-to air are such that the heat you can extract from outside air below 20F are so low that the system heat pump compressor shuts down the heat pump at 20F and you use backup heat such as a gas furnace or a 100% electric resistance heating unit indoors. Heat pumps are most efficient with small differences between the indoor temp and the outdoor source/sink. A delta 20 F ( 70F indoor-50F) source is ideal. A delta 50F (70F indoor-20F source) is just break even and is a net loss with many defrost cycles.

What I found is with my very well insulated house was that where the heat pump worked well which was in the 40F to 60F outdoor range we needed very little heat anyway. As the outdoor temp dropped below 40F, I got the defrost problem, and then at 20F and below I had to use gas 100% anyway. I have partial passive solar heat that carries much of the heat load on just cool days in the 40s. It hit -19F here two winters ago where this design heat pump is useless.

Well, as fate would have it the compressor failed just after the 5 year warranty expired. I decided to revise the old SEER 10 rated system to a high efficiency SEER 12 A/C unit and straight gas heat furnace . This was several thousand dollars less than an upgrade to a SEER12 heat pump. (Today even more efficient SEER 14+ units are available- they were not back then) Also the constant noise of the outdoor compressor/air unit running all winter was a problem for us and our neighbors. The compressor should have run 10 years, but even then having a $2000 repair bill every 10 years adds $200 per year to the cost of the heat pump heating bill, not to mention the frustration of heating failure which always occurs on a very cold day!!!

So, in some cases heat pumps make sense, but it is NOT a universal choice. A very few geothermal areas in the world have ground water that is hot. If you live in a geothermal area with 100F water 50 feet down, ( Klamath Falls, OR) is like this, then a well can be drilled and a coil put into the well. A heat pump is not needed. You just pump a water/glycol mix through the down well coil and into the house to heat!. Great, but very rare location.

[Frank]

One thing I've noticed is that there's a lot of electric heat still in use, particularly in areas where hydroelectric power is abundant. Given coefficient of performances of ~3 (i.e. 3 times as efficient as electric resistance heating) I would have to wonder if subsidizing homeowners to install these units in lieu of resistance heating wouldn't be a money-maker for utility companies. In some places it's now more economical for utitlity companies to purchase solar power from homeowners as a means of increasing capacity: why not do the same with heat pumps? Sell the conserved electricity to other areas now dependant on coal or natural gas power and make money on the deal...

In our part of the country (New England) it'd be difficult to install a ground-based unit due to the large amount of ledge. It makes a lot of sense in other parts of the country though.

[donshan]

$this->bbcode_second_pass_quote('Frank', 'O')ne thing I've noticed is that there's a lot of electric heat still in use, particularly in areas where hydroelectric power is abundant. Given coefficient of performances of ~3 (i.e. 3 times as efficient as electric resistance heating) I would have to wonder if subsidizing homeowners to install these units in lieu of resistance heating wouldn't be a money-maker for utility companies.

[Kingcoal]

The one thing to remember in understanding heat pumps is that they are all about heat flow. The problem with heat exchanger coils frosting up comes from the fact that the flow of heat from the ambient air to the coil is being stalled by the frost which acts as an insulator. If you think about it, it's pretty stupid design. Of course the coils will frost up! It's just one of many things that I find amusing in the heating/cooling industry. It's an industry that seems to lack imagination.

The other problem is the fact that air is a pretty good insulator itself. Heat conduction is severely limited at the interface from metal to air. The water to metal interface is orders of magnitude better. The problem with the well water system is that the heat exchanger must be periodically cleaned due to mineral buildup.

Well, there's always coal.

[drew]

$this->bbcode_second_pass_quote('donshan', 'I')f you could extract heat from a flowing water stream at say 50F then all is well. The outdoor exchanger stays at 50F and frost never forms. However if you place the piping just underground, then it is possible to freeze the earth surrounding the piping and eventually you can't get any more heat. So these underground systems work best with lots of ground water that moves. An experienced contractor is an absolute MUST for such underground loop systems.