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  1. #40
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338

    Re: Low delta-T

    Originally posted by perpetual_student
    Can anyone document the idea that geothermal equipment removes humidity as well as conventional AC equipment? The thing I suspect is that geo equipment in particular, will use a less-cold coil (i.e. "lower Delta-T") in AC mode than will for example, a Carrier Infinity system. Using a lower Delta-T is one way to get higher EER and SEER -- because those measurements pay no respect to humidity removal. Inferior humidity control is one of the things that I would always suspect of an extra-higher EER number.

    If indeed any system uses lower Delta-T to get that last point or two of EER, they have artificially scored a big advertising number at the expense of compromising humidity removal. In some climates that is OK, in a hot-humid climate that is a very bad trade-off.

    Regards -- P.Student


    [Edited by perpetual_student on 03-16-2005 at 06:38 PM]
    I don't have much experience with geothermal or ground loop heat pump systems, so I'm just offering my opinion. Which is if the geothermal heat pump is sized properly for the structure's heat gain and loss load, it'll do fine. Geothermal's main advantage is a more consistent heat exchange medium (the ground) than air, which varies with ambient temperature. Ground temperatures do swing but not nearly as wide or at the same rate as air, obviously.

    So, on a hot, humid day, when both sensible and latent heat loads are high, the ground source unit could, let's say, be set to maintain a steady condensing temperature of 110 degrees, whereas an air coold unit might be experiencing condensing temperatures on the same day somewhere closer to 130 degrees. Effectively, the geothermal unit will have more latent and sensible heat removal capacity under the same conditions than the air cooled unit.

    The main drawback, IMO, of geothermal loops is the added cost of the loops and the additional maintenance factor of the loop if water is used. Of course, air cooled units also must have their outdoor coils cleaned regularly to maintain performance, but this is likely an easier maintenance item than a drain, flush, and fill of a loop.

    If the geothermal OEM is trying to maintain a lower compression ratio by keeping the evap a tad warmer - hence a "lower Delta T" - (combined with reduced head pressure), then he's likely done the math to have the unit BTU rated at that evap temp to keep the building properly cooled and dehumidified.

    Even a builder model 10 SEER piston flowrater system will dehumidify adequately if it and the ductwork are sized and installed properly for the expected sensible and latent heat loads of the building. It just won't be as efficient or precise. The variable speed, TXV equipped, modulating systems do the same thing with more finesse and less energy.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  2. #41
    Join Date
    Dec 2003
    Posts
    165
    That was well worth reading! If the ground loop seems too expensive why not think about the "pump and Dump" method? If you already have a well and a good water table you are golden!

  3. #42

    Re: Re: Low delta-T

    Originally posted by shophound
    Originally posted by perpetual_student
    Can anyone document the idea that geothermal equipment removes humidity as well as conventional AC equipment? The thing I suspect is that geo equipment in particular, will use a less-cold coil (i.e. "lower Delta-T") in AC mode than will for example, a Carrier Infinity system. Using a lower Delta-T is one way to get higher EER and SEER -- because those measurements pay no respect to humidity removal. Inferior humidity control is one of the things that I would always suspect of an extra-higher EER number.

    If indeed any system uses lower Delta-T to get that last point or two of EER, they have artificially scored a big advertising number at the expense of compromising humidity removal. In some climates that is OK, in a hot-humid climate that is a very bad trade-off.

    Regards -- P.Student


    [Edited by perpetual_student on 03-16-2005 at 06:38 PM]
    I don't have much experience with geothermal or ground loop heat pump systems, so I'm just offering my opinion. Which is if the geothermal heat pump is sized properly for the structure's heat gain and loss load, it'll do fine. Geothermal's main advantage is a more consistent heat exchange medium (the ground) than air, which varies with ambient temperature. Ground temperatures do swing but not nearly as wide or at the same rate as air, obviously.

    So, on a hot, humid day, when both sensible and latent heat loads are high, the ground source unit could, let's say, be set to maintain a steady condensing temperature of 110 degrees, whereas an air coold unit might be experiencing condensing temperatures on the same day somewhere closer to 130 degrees. Effectively, the geothermal unit will have more latent and sensible heat removal capacity under the same conditions than the air cooled unit.

    The main drawback, IMO, of geothermal loops is the added cost of the loops and the additional maintenance factor of the loop if water is used. Of course, air cooled units also must have their outdoor coils cleaned regularly to maintain performance, but this is likely an easier maintenance item than a drain, flush, and fill of a loop.

    If the geothermal OEM is trying to maintain a lower compression ratio by keeping the evap a tad warmer - hence a "lower Delta T" - (combined with reduced head pressure), then he's likely done the math to have the unit BTU rated at that evap temp to keep the building properly cooled and dehumidified.

    Even a builder model 10 SEER piston flowrater system will dehumidify adequately if it and the ductwork are sized and installed properly for the expected sensible and latent heat loads of the building. It just won't be as efficient or precise. The variable speed, TXV equipped, modulating systems do the same thing with more finesse and less energy.
    Shop, I do have about 35 years of experience with water and geoexchange heat pumps. The loops have, I consider no up keep and the open systems if the flow is right and the water clean almost the same. I know of one unit that has had two service calls since it was installed in 1979. One because the water pump failed in 1993. The other because the the telephone man left the manhole cover of to the crawlspace and a dog worked on some of the duct. The only thing that has been done to this unit is changing the air filter. I wouldn,t call this additional maintenance.

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