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 - 4. 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 4Kw of energy and the cirulator pumps would only use about 25 watts each so their effect is negligable. In reality, you will see 60-70% 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.
[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
[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)Dalilas
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)Dalilas
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.
[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)
