Why not oversize?

Discussion in 'Geothermal Heat Pump Applications' started by NathanB, Jun 6, 2015.

  1. NathanB

    NathanB New Member

    Given comparable COP values why not oversize my system? I have 5 ton water to air open loop system running on an efficient VFD driven well pump. Combined COP values of 4 (heating) to 6.7 (cooling). I love never having to run emergency backup, and being able to turn house temps down at night and bring them back up quickly in morning. Also with proper duct isolation and soundproofing in utility room it is silent.

    So other than slightly higher initial costs (I designed and installed system myself), what benefits would I gain from a smaller, more appropriate size system? Is there an initial waste of electricity getting the pump started and up to pressure, how significant?
  2. NathanB

    NathanB New Member

    I guess a couple issues would be short cycling - 10 min runtime would be best for near optimum COP numbers, and dehumidification in summer A/C if heat pump doesn't run enough it won't be able to remove latent heat (humidity). Can anyone confirm or deny above? Any other drawbacks?

  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Not so much of an issue if you use the newer variable speed equipment. Short cycling is more stress on the equipment, as well as comfort (dehumidification). Both not an issue with variable speed technology. We tend to put larger equipment in there with variable speed technology. Efficiency actually goes up, since part load run time is longer. Single or dual stage will run better and more efficient if sized smaller.
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    At what pressure do you operate your system? Most vfd's are grossly overpowered in relation to gallons per minute and pressure, as well as up front costs of the box.

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