Geothermal and Solar

Discussion in 'General Discussions' started by olemartinus, Aug 14, 2009.

  1. olemartinus

    olemartinus New Member

    I live in the Texas Panhandle. I had a 5 ton Water Furnace geothermal heat pump installed when we built our home 9 years ago -- 5 vertical wells at 250 feet packed with bentonite were drilled. It did not work initially and, after much evaluation, the loops were exposed. Checking temperatures directly at the loops, we ascertainted that only 2 of the loops were functional. The well driller installed 5 new loops but utilized the two that evidenced a temperature differential. We installed pressure and temperature gauges on both sides of the loop. The return loop temperature reaches a peak of 90 degrees during the deep summer and a low of 40 degrees during the deep winter. Throughout the year, I see a supply-return differential of 5-10 degrees. Any comments about the function of the loop would be appreciated.

    I have a substantial solar thermal system at the home. I have installed 16 American Solar evacuated tube collectors with 25 tubes each for a total of 400 tubes. Next to my geothermal heat pump, I have a 900 gallon fiberglass storage tank which was heated to at least 125F each day last winter by the solar collectors. The collectors were able to heat the tank from 70F to at least 125F during a single day. The tank has a copper loop at the bottom connected to the solar collectors and three other loops: one for DHW, one connected to a radiant heating floor, and one which is unused.

    The radiant floor was supplied with heat from the tank during the deep winter, but I generally use the heat pump only during the early and late winter, since the local temperatures can vary greatly. I asked my geothermal installer if the heat from the solar tank could be used to warm the geothermal loop by going through the tank or with a heat exchanger. He did not feel that this would be wise. I am interested in the opinions of this group. Would this be reasonable? If so, how would you do it in a manner that would not compromise the WaterFurnace unit?

    Thank you in advance. I have read this site for the past few week and found this group to be very intelligent and helpful.

  2. Bergy

    Bergy Member Industry Professional Forum Leader


    I don't believe your loop temps are out of line for your neck of the woods. In East-central Iowa I would expect vertical loop temps of 80~85* by the end of the cooling season. By the end of the heating season I would expect to see loop temps of 30~35*.

    While it is possible to warm the loop field with solar, I don't see much of a benefit for your system. The amount of efficiency loss with 40* EWT is small and would not justify the cost of installing, running and maintaining the system.

  3. geoken

    geoken New Member

    I dont understand why only 2 of the 5 loops were functional. Are the other 3 loops air locked? If they are in the ground and charged with antifreeze they are functional. Also, why are you putting 125 degree water in the ground rather than into the house where it belongs? Its late and I am tired so maybe I missunderstood your question.
  4. olemartinus

    olemartinus New Member

    Bergy -- thank you for your reply. I have read many of your posts and value your opinion. Would it change your mind if it only cost $200-300 to connect the geothermal loop to the extra copper loop within the storage tank? Also, if 90F and 40F are relatively efficient, are there upper and lower breakpoint temperatures at which the unit becomes rapidly inefficient?

    Geoken -- when we installed the unit 9 years ago, the summer loop temperatures reached 125F. The unit was checked by a WaterFurnace regional representative and found to be functioning normally. The loops were flushed with no response and the pre/post loop pressure and temperature gauges were installed to appease my OCD. The individual loops were unearthed and we checked pre/post temperatures on each loop. Only 2 of the 5 loops were found to have a temperature differential. The driller suspected that the 3 non-functional loops did not contact the soil despite his filling of the holes with sodium bentonite after placement of the loops. The driller returned and drilled 5 new loops. The geothermal contractor connected all 7 loops to the 5 ton unit.
  5. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I need to think on this

    ,,,,but I can not see why not. I am a great fan of hydronic heating and if the panels are caring the DHW and the floor why not allow the solar to feed the heat pump?
  6. Bergy

    Bergy Member Industry Professional Forum Leader


    I've never been a big fan of making systems more complicated. If your system is operating as designed I would leave it to do so. Grandpa was always a big fan of two things... If it ain't broke, don't fix it! and KISS...Keep it Simple Stupid! :lol:

  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    The Btu's available in the tank could be directly comunicated to the heat pump coax, and improve the COP. but would require monitoring isolation etc.
    The is it worth the trouble question is one that you have to answer. ROI vs PITA (pain in the...) is likely out the window on this one.
    Other considerations include; max entering water temp for heat pump/tempering. Warranty considerations (if your installer isn't on board don't expect help there). At 9 years old you've little warranty left anyway (unless you purchased extended loop warranty).
    Personnaly I like the KISS principle.
    Good Luck,
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Joe, you are right, KISS,

    ,,,but it seems simple to me. We are talking about moving BTUH, not landing a spaceship on Mars.
  9. eisensms

    eisensms Member

    This stuff is definitely not simple or easy to do.
    I am going to end up going with a "commercial" control system for my home, as I am integrating Solar Hot Air, Solar Wind, a Natural Gas Furnace (as emergency backup heat), and a Water-to-Water Geo system. As for cooling, I will be taking the 50 degree well water and running it through water-to-air coils in my furnace plenum, and running the furnace fan to circulate the cool air. Then when that doesn't cool well enough the Heat Pump will kick on and the solenoid valves will close to circulate the super-cooled water from the Heat Pump fed storage tank. For heating, the Solar supplies hot water to my Radiant Floor, but there are times that the Solar can't keep up so my Geothermal Heat pump kicks in and the water flow through the system changes such that the storage tank no longer contains chilled water, but now has 125 degree water in it to feed the Radiant floor. If it gets too windy and cold, the 3rd stage Natural Gas furnace kicks on to supply the necessary BTUs, instead of using Electrical Resistance heating. To make all this magic happen, I got tired of manual opening and closing valves, so I needed to turn to a Commercial Programmable system.
    Not for the Faint of Heart!! I guess that is why I get so many people visiting my house on the National Solar Tour. Any sane person will quickly see that this is an interesting hobby, not a heating/cooling solution for a typical homeowner. For me, it is fun tying it all to my BlackBerry and putting all my individual electrical circuits on a web page to watch from work, how much energy my wife and kids are using during the day. I can tell when my wife opens the
    refrigerator door!

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