Talk:Geothermal exchange heat pump
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[edit] 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)
[edit] 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.
[edit] 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.
[edit] 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[1] 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)
[edit] 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.
