Talk:Geothermal exchange heat pump

More information about efficiency?
I'd like to know, as a function of temperature difference between ground and building-rooms, how efficient is the cooling system, and how efficient is the heating system. (In kW thermal delivered per kW of electricity consumed.) It'd be very interesting to have an indicative figure (I've heard 3:1 and 4:1) and also to have a graph of efficiency versus temperature difference (is it 3:1 at all temperatures, or does efficiency vary with temperature difference?) 131.111.48.116 11:35, 30 June 2006 (UTC) David MacKay

Intersting to note that efficiency is better in heating as the pumps and fans add heat to the output where in cooling the heat is unwanted.

--hydronics  15:38 8/20/06

This is a good, clear article, but could we have a metric conversion for "four tons" of heating, please? I've only ever seen it in regard to cooling. Does it correspond to 14.2kW, or are my factors off? --scruss 20:45, 14 July 2005 (UTC)

Scruss, The conversion from tons to Btu/hr is 1 ton = 12000 Btu/hr, and then 1000 Btu/hr = 0.29Kw. I updated the site --notyouravgjoe

What about adding something about the electricity used to run the pumps? Since ground source heat pumps are becoming more popular, there seems to be an idea that it's free and cheap. In reality, there are many factors associated with the site, as well as the expense of running the pumps. Dalilas 15:28, 7 September 2006 (UTC)Dalilas

Geothermal Heat pumps use a measure called COP or Coefficient of Performance. Most newer systems have a COP of 3 - 5. With a COP of 4 you get four units of heat for each unit used to produce it. Usually this only includes compressor and fan power, but does not include pumps. In a closed loop system however, there are also circulator pumps and desuperheater pumps that are not factored in however they are not significant. A typical 4 ton system uses about 3-4Kw of energy and the circulator pumps would only use about 25 watts each so their effect is negligible. In reality, you will see 60-75% less energy usage then the equivalent electric furnace. There is no technology that can save as much energy with a quick payback then a geothermal heat pump.

I am not happy with the statment in the article that "geothermal heat pumps perform with far greater efficiency and in a far larger range of extreme temperatures than conventional air conditioners". Data I have seen for (Japanese) air source heat pumps suggests that they have a COP in the range 3-4, so not much different from ground source heat pumps. Air source heat pumps are also cheaper to buy and easier to install, so contradicting a statment im the (unsigned)paragraph above. Could the person who wrote the paragraph above perhaps contribute some words into the artice? DMWard 12:20, 2 March 2007 (UTC)

In advance, I should state that I'm not qualified to give a definitive answer on the COP issue. That said, there are (in principle) two efficiency issues: the first is the efficiency of a given engine/technology (the heat pump), and the second the efficiency of a given system/installation (the parallel for, say, cars may be identical engines using different gearing ratios or even tires). In principle, air conditioners and geothermal heat pumps use the same technology, so the efficiency there should/could be identical (in terms of work per unit of energy). Geothermal pumps get their installed efficiency advantage (compared to air source heat pumps, i.e. air conditioners) primarily from the fact that they are dumping the heat to a naturally cooler heat sink. Or to put it a slightly different way: an air conditioning system will be more efficient at an ambient air temperature of 70 degrees fahrenheit (to cool to, say, 65 degrees) than it will be at 110 degrees. Since the ground temperature might be 40-50 degrees, the ground source heat exchange system will cool more efficiently - dumping the heat is less costly (and compressing a cold gas takes less energy than compressing a hot gas). It can also work in a larger temperature range: any heat pump will have a temperature beyond which it won't work well (possibly at all?) - as the ambient temperature gets higher, less cooling is possible. I think there is actually a technical limit, but this needs to be confirmed: if the exchange medium (cooling fluid) expands at a heat level that is equal to or lower than the ambient temperature, heat exchange may stop being possible or practical.--Gregalton 10:22, 7 March 2007 (UTC)

Loop lengths??
I have a problem with the facts on this page. The rule of thumb for the ground loops of 300' vertical loop and 400' of horizontal loop are inaccurate. It depends on where you are located. In the midwest for the closed loops (from OK to MN) the rule of thumb is 150'/ton vertical, and then there are several breakdowns for horizontal. I will consult ASHRAE and see what I can find out for accuracy and edit the page.

--notyouravgjoe  15:38 11/9/05

Actually loop length is mostly dependent on soil type, whether the soil is sandy or clay or dry or moist. Dry sand requires more loop length then moist clay. It's based mostly on the conductivity of the soil.

SOLAR PANELS
Is it possible to use a heat pump (comressor/evaporator/glycol) running within solar panels. 7/7/06 Rich Lewis

Search "Copper Cricket" to learn about a water heater that uses a refrigerant that undergoes a phase change in the collector.... really cool and zero pumping energy.

--hydronics  15:38 8/20/06

Yes, but it would take a significant solar system to do it. Although they are extremely energy efficient, you would still need approximately a Kw of available power per ton of capacity any time the system is running.

Cons?
Aside from the expense of running the pumps and site positioning (what is your soil type, what surrounds the land, how warm is the soil...), I wanted to add the idea of the possibility of too many users. The ground temperature could be heated or cooled too much when there is a high density of pumps. This can cause the ground to heat or cool too much and would affect the functioning of all of the units over time. The efficiency of the heat pumps would then be lost. I know of an industry that used heat pumps for many years to refrigerate. The ground around the area is now much warmer. This can affect groundwater patterns and frost patterns among other things... Dalilas 15:38, 7 September 2006 (UTC)

I found a reference for the area I was referring to: Ferguson G. and A.D. Woodbury. 2005. Canadian Geotechnical Journal 42: 1290–1301. You may be able to view it online through NRC Dalilas 18:44, 7 September 2006 (UTC)

This could possibly be an issue where the use is exclusively for heating or cooling year round. In most cases, these systems are used for both heating and cooling, which reverses the flow of heat from season to season, tending to balance out. In fact it is usually recommended to install GS systems where both modes are required. The ground actually tends to be more efficient at the beginning of one season or the other due to heating or cooling of the ground from the previous season. To lose the advantage of GS system would require a major drop or increase in temperature which is unlikely. It could, for example, decrease the COP from 4 to 3 if there is a change from 55F to 45F ground temperature. It is very difficult to get too far away from the normal ground temperatures, as a large differential from the surrounding area or depth will actually cause more heat to transfer to or away from the area due to the laws of thermal dynamics.

I live in Canada and the cooling season is very short. A well-designed house doesn't need cooling; with continual heating being used, the ground can cool. I could also see the inverse being the case in Australia, for instance. --Anyway, I think it's important to qualify your recommendations based on use. People are starting to see ground source heat pumps as a "fix" for heating (at least where I live) and haven't aired the drawbacks enough. With a lot of people using heat pumps, it isn't difficult to "get too far away from the normal ground temperatures" (as my example above and the paper by Ferguson and Woodbury show). Dalilas 16:33, 15 January 2007 (UTC)

I personally live in southern Ontario. I have used a 4 ton GS system for 3 years, and have kept ground temperature data since I have installed it. I have a very inefficient house built in the early 70's, and have sandy soil which is the poorest type of soil for a GS system. I have an extra loop to compensate. I use air conditioning for about two months a year, two months with little use, and the rest for heat. In the three years I have used this, the ground temperature variation from year to year in the same month has stayed constant for the whole time. If there has been a change from year to year, it's not enough to measure. —Preceding unsigned comment added by 66.46.13.221 (talk) 21:54, 27 February 2008 (UTC)

Image
Does anyone know what this is a picture of? (The filename translates to "geothermic probe"). Why is it included in this article? Yabbadab 19:45, 6 December 2006 (UTC) I agree. It's not a helpful photo at all.Dalilas 16:38, 15 January 2007 (UTC)

Yes, please remove this picture. It's irrelevant.

It's not that it's not relevant, it just needs a caption that explains what it is and how it relates to geothermal exchange heat pumps. 65.185.88.200 21:48, 23 May 2007 (UTC)

Where (geographically) will you need a ground-source (vs air-source) heat pump?
Where is the dividing line (in North America) where an air-source heat pump is not sufficient for winter heating and a ground-source pump is therefore needed? —Preceding unsigned comment added by 65.93.87.81 (talk) 14:38, 14 November 2007 (UTC)

Air source heating efficiency drops off significantly below freezing. Any area that has significant below freezing temperatures in winter is much better off with ground source heating. Many air source heat pumps reach unity (where heat energy produced = energy used) around -10C. Supplementary duct heaters can be used to overcome this, but given a choice, ground source is always better. The main downside is initial cost. Air source are cheaper initially, but in the long term ground source is cheaper in both energy costs and maintenance. —Preceding unsigned comment added by 66.46.13.221 (talk) 21:44, 28 February 2008 (UTC)

GSHP requires compressing refrigerant? (!)
I'm definitely missing something here. I thought that the GSHP approach completely got away from using compressors and refrigerant. That the heating / cooling was accomplished via circulating (not pressurized) a liquid thru piping buried in the earth, and pulling out the Earth's heat in the winter, and sinking the building's heat in the summer.

Running a compressor would just about demolish any savings one is trying to achieve by getting away from 'conventional' (ie: compressor-based) systems. What am I missing? 68.228.82.130 (talk) 12:18, 27 November 2007 (UTC)


 * You are only missing a minor point: that the earth's heat is too low in the winter. Say it's a constant 6-10 degrees, this would be a bit chilly. The compressor "pumps up" the temperature differential (since it may be used for hot water as well, this would be much lower than needed). And of course, even if you were not pressurizing, you would be pumping the liquid anyway (which also consumes energy); if I'm not mistaken, the pressure differential at each stage drives the circulation, so you save somewhat on the pumping. (Isn't a pump somewhat similar to a compressor anyway?). And, the savings do exist.
 * For the cooling phase, in theory you're right that the liquid/gas could just be pumped. The savings over a "conventional" air conditioning system is that the heat sink (the ground) is already much cooler than the outside air (still at that constant temperature), so it's much more efficient (less pressurizing that needs to be done). Put another way, imagine you kept your refrigerator/freezer outside in the late fall - ambient air is already cooler, so it costs less to run than it would inside your toasty-hot residence.--Gregalton (talk) 15:17, 27 November 2007 (UTC)

What you are talking about above is passive cooling in relation to active cooling. There are many ground source heat pumps available that use passive cooling (without a compressor) rather then active cooling with a compressor. The one downside of passive cooling is that you do not get desuperheater hot water heating in that mode which offsets the energy of running the compressor. Essentially, you are taking heat from your house and putting most of it in your hot water with a desuperheater installed in active mode. In this case, it's usually more cost effective to use active cooling. Note that heating mode is always active. Passive cooling is most cost effective in systems that don't use hot water or heat with other methods. In Toronto for example many hi-rise buildings do not require much heat, due to heat rising through the buildings, and have higher cooling requirements. Many of these buildings use passive cooling from Lake Ontario, and do not use a compressor at all. —Preceding unsigned comment added by 66.46.13.221 (talk) 21:33, 28 February 2008 (UTC)

Better description operation GEHP (soil storage) operation plus picture and coinage term "heat and cold storage"
A better description can be derived from this text I created (you may also include it as is; no copyrights on it):

This system combines water/humidity application together with seasonal subterrainean heat and cold storage. In the system, the water is not only used to water/humidify the plants (in a closed circuit), but is also used as a storage medium for heat (held in a underground aquifer) aswell as for the cold (in a 2nd aquifer). The heat and cold stored in the water mass is when needed spread as hot or cold air trough the use of fans. In the described system, everything can be automated. Optionally, the primary heating can be done by heat pump (which derives heat from the outside air or soil)
 * GEHP operation for greenhouses (with Hortimax-automation)

An extra schematic picture can be found at: Heat and Cold Storage http://www.iea-eces.org/energy-storage/storage-techniques/underground-thermal-energy-storage.html Automation of underground Heat and Cold Storage system by Hortimax http://www.hortimax.com/content/Multima_water.aspx

Finally, also mention the term "heat and cold storage". Aldough its not the correct term, it is often used as the primary description by the leading organisations.

Please shift trough the info provided and use it to clarify the article. Thanks.

KVDP (talk) 09:47, 21 January 2008 (UTC)