How fast should EWT increase when geothermal heat pump system is in use?

Discussion in 'Maintenance and Troubleshooting' started by DannyB, Jul 24, 2010.

  1. DannyB

    DannyB New Member

    Hey guys, I was curious how fast EWT should increase when the system is in use .

    I have a closed ground loop system (8 x 85 ft wells that are piped in parallel), and a 4 ton Envision system.

    The EWT when we started (a few days ago) was 82 degrees.
    Today it has varied (it was 110 air temp outside today, so A/C has been on a bit) but at points was up over 105 degrees. It's now back down to 92.

    I'm curious how fast the EWT should be increasing when the system is in use, and decreasing when it isn't.

    (If it matters, a red herring to throw around: the system was installed 4 days ago)

    I haven't measured the pressure differential because my adapter for the pressure gauge won't be here for a few days, so i'm not positive of the flow rate yet.
    Last edited by a moderator: Aug 29, 2010
  2. newgeohp

    newgeohp New Member

    I'm sure this is like comparing apples to oranges, but I have 2 ton unit and 1 well at 265' that is 2 months old. Every morning my loop temperatures start at 65-70°F and on normal days with outside air temperature getting to 90-95°F my loop temps will climb to around 80°F. My loop temperatures will drop about 5°F when the unit is not in use for about 2 hours. Today in Virginia we got up to 102°F and my loop temperature is at 85°F. I'm not an expert and just thought I would share my data with you even though there are a lot of other factors that can effect loop temperatures (soil type, rock, grout type, and many other things). I think most units will work fine with EWT of 105°F with proper flow rates (check your specification sheet) just not as efficient, but you may just need to watch it for a while. Right now your sample size is pretty small and the weather is a little bit on the extreme side.

  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    As a general rule systems should be designed so the at EWT isn't much more than deep ground temp + 20 during summer and -20 during winter.

    EWT of 105 suggest the system is underlooped or has some other issue. Then again, an outdoor temp of 110 is quite extreme - where is this system?
  4. DannyB

    DannyB New Member

    Montgomery County, Maryland.
  5. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader


    It is allways about the design, degree days, and anticipated temps. This heat wave we are experiencing here in the mid atlantic region is unprecedented in recent history. It is doing a really good job of identifying systems that were designed to tight or were marginaly correct from the start. I looked at two more systems over the weekend with a ewt in the high 90's. Many of you know that it is allways the well drillers fault, so I allways get an invite to the party.
    The two I looked at over the weekend were the exception not the rule. When I questioned the installer about the cooling load numbers, number of degree days planned for, and at what temprature, they both went "deer in the headlights". Yesterday on my patio I recorded a max temp of 117F. Can you say extended run times?
    If you can get the data from your installer you will be able to determine the design parameters for your system. The bad news is the higher the ewt gets the lower your capacity to cool. Hope this helps.
  6. geome

    geome Member Forum Leader

    Guess that's why our system is making lots of hot water. :)
  7. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Some of that makes sense. If at design day loads a system might run 12 hours per day at a 20 deg rise in EWT above deep ground temp it is not unreasonable to expect that during this really ugly heat wave a system running 18+ hours per day might push EWT up quite a bit more.

    In the case of a Maryland system under extreme duress EWTs in the 90s or low 100s might not be unreasonable, though capacity and efficiency both fall.

    That said, air source heat pumps similarly suffer when the outside air temps exceed 100
  8. WF_Inc

    WF_Inc Member


    The entering water temperature will depend on variables, such as the design of the system, unit run time, outdoor weather conditions, etc. Temperatures have been unusually warm this summer. In order to satisfy the desired temperature in the home, the unit may have to run longer; which may result in increased entering water temperatures.
  9. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I've not researched it, but a 4 day old install could suffer slightly. Grout (like concrete) may discharge some heat when setting which could impact performance short term.
    This unit really hit the ground running.
    Thoughts anyone?
  10. newgeohp

    newgeohp New Member

  11. DannyB

    DannyB New Member

    Just to put an update on this thread:

    So they came by (just now) with a more powerful flush cart, and there was definitely some air left in the system (and by some i mean you could hear it throughout the house when the air came out)

    But there is still a bunch of air/something stuck in the system coming out, they think so they are going to dig up the manifold and try to isolate from there.

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