Pre-Heating of water going back into wells for later use
Last Post 15 Dec 2012 11:30 AM by geodean. 12 Replies.
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Fred2010User is Offline
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28 Nov 2012 10:58 AM
Wanted to get some feedback on an idea. 

I have a Geo HP and only use it for heating (no cooling).   The  system utilizes 2 300' wells into granite and are grouted.    I have an opportunity to acquire some flat solar panels for hotwater.    I am wondering if I can use solar gain through the spring-fall to circulate the hot fluid back into the ground and heat up the rock and grout.   (Of course i would consider using for my domestic hot water)  It would have a valve set up and would only run the circ pumps when the fluids are being heated.   I could use a buffer tank or just go direct.

Right now my field water is coming in at 46F

Or using a  wood stove to heat water.



Have anyone done something like this or aware of this concept?
waterpirateUser is Offline
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29 Nov 2012 06:12 AM
Applying pasive solar heating to your loops via a plate exchanger can be done. The amount of gain vs. the benefit the system sees and the cost of install would be the detractor.
Eric
Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center!
joe.amiUser is Offline
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29 Nov 2012 10:36 AM
yur loop temp is great. make domestic hot water and call it good.
Joe Hardin
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engineerUser is Offline
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29 Nov 2012 10:37 PM
Time and again I read of schemes and claims that summer air conditioning stores heat underground for winter use and vice-versa, as well as various schemes to store solar heat underground, but never any data supporting the concepts.

While there is some indication that very large commercial borefields (100+ holes) may exhibit multi-year temperature changes, I doubt any residential system would ever exhibit similar behavior unless 100 houses in a dense subdivision all had ground loops. Two effects militate against storage across seasons:

1) Shoulder months - each spring and fall there is a month or so where little home heating or cooling occurs. In Maine those months might be May and September, while here in north Florida the slow months are March/ April and October / November. Residual heat dissipates during those weeks.

2) Many bores pass through one or more aquifers. Aquifer advection (sideways movement of ground water) operates to carry away any stored heat from all but the biggest borefields.

This is my understanding, not based on hard data or personal experience, so I'm open to feedback.
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
waterpirateUser is Offline
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30 Nov 2012 05:51 AM
There is a loop field in my OA that has 1-1/4 x 600' bores that failed. It penetrated at least 4 aquifers that could be identified. It continued to store heat untill the ewt would not provide cooling anymore. This occured over a period of about 5 years. The shoulder months were not enough to save it.

I think that aquifer advection is grossly over rated as a correcting factor. The ability of the grout to insulate the loops whilst protecting the aqifer is another thought that comes into my mind here.

We toyed around with the idea of using passive solar to warm a loop that would only be used for heat. Given our access to time, equipment, and barley based adult beverages, even we abandoned the concept as just a fancy.
Eric
Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center!
jonrUser is Offline
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30 Nov 2012 09:02 AM
Advection (ground water flow) rate is highly site specific and plays a very significant role in many bore fields.

If yours is in granite without groundwater and you have a nearly free source of heat, then it might pay for itself, especially on the days where you have excess solar heat during the heating season (ie, only storing for a few days).
jokinUser is Offline
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30 Nov 2012 09:43 AM
This topic has fascinated me for some time.  

There is only one local project that I know of that is doing this in West MI, and it is a commercial borefield.  GMB an Engineering firm based out of Holland, MI does full service arch/eng work, but specializes in commercial geothermal.  They partenered with a local commercial grower who uses geothermal to heat their greenhouses in Kalamazoo, MI (no cooling involved).  In 2009 or 2010, they installed solar thermal panels to help "charge" their borefield.  I haven't heard or seen anything on the results of the "solar charging" project.  

As someone already noted, it would seem really easy for the entire "solar charging" project to go negative in the overall life cycle cost compared to just plan geothermal, once you account for additional pumping power, cost of the panels/piping, life of the solar panels, and additional maintenance.  

I would think alot of field testing/bores and a solid modeling tool/software would be involved to know if this concept would payoff and how to best operate or control it, since there are so many variables (ground conduction, borefield size, collector size/type/allowable or achieveable temperatures, fluid flow rate/pump speed, weather/cloud cover, etc.)

Depending on the above variables, is there a point as the ground warms that the the heat flow into the field is less than the pump energy expended to circulate the fluid?   

If this took place before the heating season starts, then the energy benefit is erroded over the time between that and the start of the heating system. 

Finally, would putting the project cost of a "solar panel charging" into expanding the borefield have the same or better overall lifecycle cost ?? 

An intersting project that is using this concept is Drakes Landing in Central Canada.  See there web page with live data here....  http://www.dlsc.ca/    


joe.amiUser is Offline
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30 Nov 2012 10:05 AM
Aquifers can certainly raise the efficiency of a loopfield, but since they are a bit migratory, one would not want to bank on them. All the aquifers in the world will not save a short looped system.
Commercial applications are the only ones where I have seen proof of btu banking in studies that indicate a fractional or 1F change from one year to the next.

Solar contribution to heating is regionally effective though it often tends to offer least when demands are highest.
Using solar to improve ground loop heat pump efficiency may be best done with a plate exchanger or hydronic fan coil (one would need to ensure coil circulator shut off when water was cooler than geo LAT). Loopfields still would need to be designed as though solar is not there.

If one wished to bank solar, I would lean more towards a tank of water than the soil surrounding ground loops.
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
jonrUser is Offline
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30 Nov 2012 01:17 PM
I agree - if you have the space and $ for it, an insulated water tank is a better way to store heat without degrading it.
Fred2010User is Offline
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30 Nov 2012 03:25 PM
Hmmmm  lots of feedback.   I guess I should be happy with my 46F in and 38F out temps  :-)

I appreciate your thoughts.  Always good to hear perspectives and ideas

Palace GeothermalUser is Offline
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30 Nov 2012 08:14 PM
If a loop is colder than the normal ground temp, adding heat would help the temp get back to normal. If you are trying to raise the temp above normal, then a lot of it will be lost to the surrounding ground.
Dewayne Dean

<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system
Fred2010User is Offline
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15 Dec 2012 10:32 AM
The readings have been consistent for about a month (turned on the system in early OCT and the system was only heating the house in the morning). Now that we are into the upper 20s/low 30s during the day and nights the system is kicking in several times per day. When the HP kicks on the field temps are 45-46F and after 10 min it goes to 40/41 and after 2 hrs of running stabilizes near 39/40. Leaving water temp is approx 4.5/5F lower. This is about the same as Jan 2012. We did not use the HP for cooling.
Palace GeothermalUser is Offline
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15 Dec 2012 11:30 AM
Those numbers look pretty typical
Dewayne Dean

<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system
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