Going into second winter with Geothermal, still not happy

Discussion in 'Maintenance and Troubleshooting' started by thundermustard, Nov 21, 2013.

  1. thundermustard

    thundermustard New Member

    Our geothermal closed loop system was installed almost two years ago. Or rather installation started two years ago, didn't actually finish till the following Feb. We had a bad contractor!
    They installed a 6 ton unit (GeoExcel) in the basement for our 3500 sq foot two story house. Water running to an air handler in the basement and to one in the attic. Really generally only one floor needs conditioning at a time. In the summer upstairs, in the winter down.
    The installer put in one 300 foot deep kelix well along with a trench of slinky pipe running about 100 feet. It appears the installer was overly optimistic on this well's ability to handle the load. My loop temps got into the mid 20s last winter and it even froze up. We added a standard 500 foot well last spring and while loop temps are now much better I am not seeing the energy savings I anticipated.
    This summer it did seem to keep the upstairs cooler better but I didn't see much of a drop in energy usage. I know it is hard to compare season to season as some are much hotter or cooler than others.
    Either way, or electric bills are higher using Geo for cooling than they were with ten year old AC units. We no longer spend money on oil to make hot water in the summer, so there are some savings there.
    We are now early in the heating season with two wells and my electric bill was much higher this Nov. compared to last.
    The unit does seem to keep it nice and warm. I keep it set at 70 and if I bump it up to 71 at night it will actually get there and shut down after awhile. Unheard of a year ago.
    Today I turned off the desuperheater after reading that is the general consensus on best winter operation.
    I checked the loop temps and I am running about 44 in and only 42 out. Isn't a drop of 2 degrees very low?
    It is a two stage compressor so maybe the fact it was only 4 degrees low accounts for this.
    I checked my HP and it is set for the default settings which is where it was when it was installed.
    I have the HP set temp way up to the highest (120F) with hopes of avoiding oil usage. I probably ran it in the 110 to 114 range last year. But I figure that evens out as running longer at the lower figure trying to overcome the cold outside.
    Any ideas on why I am not getting much better electric bills with double the size loop?
     
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    As you pointed out you are making hot water with the system so it does add something that perhaps wasn't on the electric bill before.
    I don't know where your "general census" about DSH's came from, but it is not the opinion of the pros here. It is generally the shared opinion of the ignorant who think it is only advantageous (or only makes heat) during cooling.
    The DT of water through the system depends on many things including GPM. Without that number no one can tell you if 2F is high or low.
    Geo should be less expensive to run than fuel oil, but 120 F is not a very efficient set point.
    It would be interesting to know many of the things on the troubleshooter checklist i.e. heat load, location......
     
  3. thundermustard

    thundermustard New Member


    I am always intimidated by these type exchanges where I am so less informed than most users, sorry for my ignorance.
    I am in Southern NH. Headload I can't help you with, I think they simply used sq footage.
    The spring after the geo was installed we did get an energy audit from our power company and we did upgrade the insulation, you would think that only would have lowered our bills a bit, it didn't.
    I believe it is less expensive than fuel oil. It isn't less than a ten year old pair of AC units though.
    I was just very shocked that our mid November electric bill with two wells vs. one well was so much higher. I don't think it was particularly colder this year.
    So if one wanted to troubleshoot themselves how would one tackle this?
    Or should I just find a competent installer to do a test? What would I ask them to look for?
    And what is DT?
     
  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    DT is short hand for delta T, or the temperature change through the machines. (Stephanie says I should say temperature rise or fall.)

    It is possible to do a good job of testing what is going on in the system if you have test tools.

    I design/build water to water systems and know them well. Have tools and do travel.

    I do not have the time to type a list of things you should test, now, but will do so later if no one else chimes in.

    The best results with any heat pump is to keep the delta T as low as possible. I agree with Joe that 120* water out of the heat pump may be a bit to high.

    What are your heat emitters like?

    Mark
     
    Last edited: Nov 23, 2013
  5. thundermustard

    thundermustard New Member

    Heat emitters means how is the warmth delivered to the house?
    If so, the hot water runs to an air handler in the basement.
    The second stage is a oil burning furnace that turns on hot water baseboard heating, it also sends much hotter water to the air handlers.
    I might add, I have a good sized bonus room over the garage that is baseboard hot water heat only. Not officially part of the geo setup. I do have a switch flipped to keep it from activating the boiler. So it gets 120 degree water delivered to it. As we get further into winter I will flip the switch and allow it to activate the boiler. I know this setup will cause a lower loop temp.
    So how do you figure out the best temperature to use? My thinking was with two wells my loop will not be stressed so max it out at 120. Keep the second stage from coming on as much as possible.
     
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Don't lose that thought. I may be able to fix this from Cleveland.

    BBL

    Mark
     
    Last edited: Nov 23, 2013
  7. thundermustard

    thundermustard New Member

    To give you some more info, when my original installer saw the loop temps in the mid 20s, he decided to unwire one of the two pumps in the holding tank in my basement.
    This did not give any LP errors and the temps did come up, his reasoning, the water was moving slower through the loop and having longer to be warmed.
    I just went down and got a reading of the return loop with two and one pump running.
    With both pumps running it was at DT of 6 degrees, much better than yesterday, the exiting loop temp was 37.4.
    I unhooked one pump and got a DT of 8.7 with a exiting loop temp of 34.6. Sounds much better but is it?
    I have also adjusted the set temp at 115.
    Thanks for your assistance.
     
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    It would be nice to know how the system is piped.

    Unless the air handler water coils are home made, there should be a table in a manual that tells the BTUH output at various water temperatures. With that information and the piping diagram we can determine if the system is doing all that it can.

    The objective of using a geothermal machine in a system is that with $4.00 of heat for every $1.00's worth of electricity the geo gives you your best value, think cheapest fuel, for heating. Therefore you want a design that lets the heat pump run all the time when there is a call for heat.

    There should be a table in the heat pump I/O manual that will show what the output of the unit is under various conditions. Comparing those numbers to the numbers for the air handlers we then can learn what is possible. Then we can look to the heat loss for the home and determine how much additional heat would be required on the design day for your location.

    The above is all heat pump 101.

    The first chore is to do the heat loss. Then we can determine how what you own can do the best, (cheapest) job.

    Mark
     
  9. thundermustard

    thundermustard New Member

    We are getting back to the basics as opposed to my initial question.
    Why with two wells would my electric bill have gone up over last year?
    Heat loss, load, etc are all the same as last year.
    The only variable is outside temperature which was pretty close to the same.
    It does a great job keeping the house cool and warm, it just hasn't been cheaper with double the loop size.
     
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    A few degrees more or less in the loop does not affect efficiency that much, but very warm load temps (output temps to the air handlers) do. The difference between the source (outside loop) temp and the load (the temp going to your air handlers is called the lift, which is the key factor for efficiency. So if your source temps are in the mid 30s, and your load temps are at 120F, that means you have 85F lift. Every degree in reduction in lift gives you about 1.5% higher efficiency, you bumping up your load water temp from 110F to 120F did cost you about 15% efficiency, about the same what you have gained with the increase in source temperature but doubling your loopfield.

    You have a very inefficient design, going from water-water to air handlers, you loose 10% efficiency in the heat exchanges. You also must have an outdoor reset control in order to lower the load temperatures on warmer days.

    You are in the beginning of a long journey here, since your contractor seems to lack an understanding about geothermal heat exchange and efficiency.

    The best way to start here is to draw up a design schematic of your system, with as many details as possible (pipe size, pump model number etc).
     

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