Kentucky Is it normal that heat output has dropped at end of season?

Discussion in 'General Discussions' started by Jmac55, Feb 21, 2015.

  1. Jmac55

    Jmac55 Member

    A general question...

    Hopefully nearly coming to the end of a very cold week here in Ky and near the end of the heating season.

    I sometimes turn off the aux heat (electric) to see how the geo is performing on it's own.

    At the beginning of the season it would put out 92.f.

    Near the end of the season (and after days of below zero f temps) it's struggling to put out 82.f!

    I understand that the loop temps will drop over the season, but does this (should this) always produce lower heat output at this time of year?
  2. Bergy

    Bergy Member Industry Professional Forum Leader

    For the most part, a properly sized heat pump will require strip heat. By turning off the breaker, you may be forcing the geo to extract more BTU's from the loop than it was designed for.
    Palace GeoThermal likes this.
  3. dgbair

    dgbair Just a hobby Forum Leader

    Have a look at your performance charts for the unit to be sure... but say your loops temps started out at ~60F and now they are ~30F... a 10F drop in air temp would be normal for my unit.
    Palace GeoThermal and Jmac55 like this.
  4. Jmac55

    Jmac55 Member

    Thanks, will keep in mind.
  5. Jmac55

    Jmac55 Member

    OK, just what I needed to know.
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Units have higher capacity at warmer EWTs. What you describe is normal.
  7. TurboTom

    TurboTom New Member

    In very cold temperatures isn't the HP going to run 24/7 regardless of whether the auxiliary heat comes on or not? And shouldn't the loop, if properly designed, be able to keep up with the HP? How can the HP extract more BTUs from the loop than it was designed for?
  8. pfer10

    pfer10 Member

    I agree. I think I would always want to be able to run the geo 24/7 if needed. Jmac had to have some field length added on after the initial installation so he was pushing it from the start. I would think that if you had a device that was capable of pulling 24k from the loop you would want the loop be able to provide 24k for continuous operation. I guess it isn't always designed that way and as loop temp goes down so does the output. I think Jmac's strategy is he doesn't mind the temp of the house to fall a little if the house is loosing 28k and his geo is only putting 24k into the house.
  9. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    A better way to look at it is a geothermal system is based on equipment run time. How many expected hours a month is that equipment running.

    Loops are not designed to produce a set amount of btu/hr. There is no 5000 btu/borehole equation.
  10. Jmac55

    Jmac55 Member

    I have to say...that turning off the aux. temporarily is simply to asses whether the output temps for the geo. had dropped significantly.

    Just figuring out what the system can do.

    My thermostat doesn't tell me when Aux is running. But I think I've read on here that I can buy one that can let me know what percent it uses. Any recommendations?

    I may invest in the future in a monitoring device that will let me see real time how it's all running, although I guess that would be more expensive so may have to wait.

    Thanks all .
  11. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You got a point.
    If you design a system with aux heat you can make the unit and the loop field smaller. Most of the time this is the most efficiency design. But if you design without supplement heat for 100%, you heatpump must have a larger capacity, which then is able to pull more heat out of the ground, which then might require a larger loop field.

    In the real world, the supplement heat is usually 1-3% of the total annual BTU, which can be 25-30 % of the peak BTU needed. This is the whole point about supplement heat. You can make the system significantly smaller (and cheaper) if you cover 1-3% of the annual load by supplement heat. That usually does not change the loop field very much.
  12. moey

    moey Member

    How? Doesnt your house just get colder?
  13. jk96

    jk96 Member

    I'm wondering the same thing. If your calling for aux heat wouldn't your unit still be running 24/7 regardless? Aux just kicks on long enough to keep the temps from dropping.
  14. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    If you're aux. is shutoff you may never notice anything.

    If you are running your system continously and not reaching a setpoint because you've turned off additional staging, you are putting additional demands on the loopfield. Your EWT's will likely drop (quicker) and your outputs will decrease. And you end up spiraling down to some lockout conditions potentially.
  15. jk96

    jk96 Member

    I understand what your saying although my understanding is that as you reach design temp your unit would be running 24/7. As you drop below design point your aux heat would kick in to maintain temperature. The use of aux however would not alter the run time of the geo side would it? Wouldn't it continue to run 24/7 at or below design temp regardless of aux use? If so, I don't see how the use or non use of aux heat would affect loop temp or performance.
  16. moey

    moey Member

    Assuming its 0 degrees for a 48 hour period and you have a setpoint of 70 with no type of thermal gain. The system should run in stage 2 for all 48 hours with aux heat coming on periodically. Or it would run in stage 2 for 48 hours with no aux heat and the temp in the house will drop. How is this more demand? Read on.

    The other scenario which Im starting to see using the same example is after the 48 hours with aux heat off is the house is several degrees below a setpoint and the sun comes out. The system has to continue to run to bring the house back up to the setpoint. Had aux heat been on it would have shut off or went to a lower stage. Is this the scenario your alluding to?
  17. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Design temp is a certain amount of (bin) hours a year. In theory, your system is designed for a certain amount of EWT to satisfy your loads at design temp.

    By shutting off the aux. stage you will have the unit running continuously at that point without reaching the setpoint.

    Moey, to address your example. As a possibility, the unit would likely run for 2 hours and then trigger auxiliary. Reach setpoint after 1/2 hour and shutoff. Turn back on 30min later. And repeat.

    I'm of course stretching things to make a point. We're not necessarily talking a day or two. We're talking in weeks/months where this can become an issue.

    Another way of looking at it.

    I'll design a system to match your heat load at -24C with 0C entering water temperature.

    I'll want to only see that low EWT at the tail end of winter. If it shows up in December, then it may be a sign of issues to come.

    Now if you have oversized loops, equipment, whatever. Just leave the auxiliary breaker off if you want.
    moey likes this.
  18. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I am not sure that the assumption can be made that with supplement heat the geossystems reach their set point and shut off.
    Usually the thermostats work in a way that 0.5 degrees below set point activate 2nd stage, and then another degree down activates supplement heat. All our systems work in a way that the second stage run continuously, and the supplement heat adds extra BTUs in cold ambient temperatures, but when that is satisfied the set point to turn off the 2nd is not satisfied, so the heatpump continues to run. See above.
    So if you shut off the supplement heat, your house simply gets colder, and the only extra load on the loop I can see is at the end of the cold span, when the HP runs extra time to bring the house back up to set point temperature at the end of a cold span. Last week the cold span was about a week...

    I can't see the additional load to be of such significance that it will reduce EWT measurably or even produce lockout scenarios.
    moey likes this.
  19. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    Sure, if you let the house get colder. Then sure that's how it would work.
  20. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    May be I am just getting confused why the unit would shut off after the aux heat brought up the temperature to the point where the aux heat shuts off, but the set point where the compressor disengages is not reached yet.

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