Dual Capacity Residential Copeland Scrolls

Discussion in 'Geothermal Heat Pump Applications' started by HVAC Technician, Jul 23, 2011.

  1. Most of us know that these compressors allow us to operate more efficiently through out the year by varying capacity according to need, normally determined by a high quality thermostat.

    Here is my queston for the engineers: I have experimented with running on 67% capacity in the summer by using the 170 # 2 option in the Honeywell Pro Vision 8000 with the following results: very good dehumidification (@ 50%), good comfort levels, and of course the sensible heat floats up and can remain 2 - 5 degrees higher than set point depending on the temperature outside, which right now is @ 100 degrees.

    Generally, with the exception of 101 - 102 days and 94 degree nights, the temp would slowly work its way back toward setpoint after the sun goes down.

    One nice thing about about this is that the compressor just chugs along with little on and off.

    Those of you with the scientific calculators; thermostat settings not changing, would there being any difference in total KW usage between 67% loading and 100% loading (which really is a call that goes back and forth between Y1 and Y2 as determined by the thermostat?

    We would of course reach setpoint quicker on 100% loading, but in fact we never stop running or dehumidifying on 66% capacity which is drawing 1 1/2 amps less than full capacity.
  2. Designer_Mike

    Designer_Mike Member

    From my limited understanding:
    The full capacity setting is less efficient (comparing BTU/W) and the exact numbers are reflected in the EER numbers for your unit. It IS a significant difference (somewhere around 30% less efficient from a quick look)

    You are also probably seeing better (overall) dehumidification having a longer run time. As long as you are comfortable with it running strictly on stage one, I believe you are using less energy than cycling to stage 2 and occasionally shutting down.
    I'm not familiar with that exact thermostat, but I believe you should be able to adjust the gap before stage 2 is activated. That might help with those really hot days.

    The trouble is, once the stat changes to stage 2, it might stay there until your temperature setting is reached and then it will shut down completely. Another possible programable setting maybe?
  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    As noted, units are significantly more efficient on low stage. Finding ways to limit high stage operation to only when it is really needed will pay off.

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