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  1. #1

    Heat Pump Comparison Outlet temps

    We have two Trane systems in a two story home. The upstairs unit in about six years old 3 ton that runs at one indoor blower speed summer and winter. The new unit downstairs is a Trane TAM8 with a XL20i outdoor unit two compressor 2 and 4 ton that is variable speed. This is a fairly new system for the Trane with the Comfort Link stat.

    My question has to do with indoor vent outlet temperatures. On any specific winter day, the upstairs unit is discharging warmer air at the fixed higher speed than the downstairs high efficiency unit at the variable speeds (the downstairs varilable speed blower is producing less air movement at vent than the upstairs unit). The upstairs thermostat is not showing auxillary heat being applied.

    I would have thought the higher efficiency unit would put out much warmer air especially when the air is moving slower. Can anyone explain why the high efficiency unit is not as warm.

  2. #2
    Join Date
    Sep 2003
    Location
    Portland.OR
    Posts
    313
    Heat pumps move BTU, the temp is affected by many factors, If not properly charged
    duct configuration and insulation of them. Air speed.. Each system has a totally different
    duct setup Im sure.. Its just not a simple: Its "more efficient so it should be warmer...
    Thats the simple overview. Usually lower blower speed will raise the temp.. Variable speed
    is looking for volume [CMF] Get your installer to lower the volume some to raise the temp.
    Heat pump range temp can be 91 [18 year old trane] to 120 degrees [8 year old Rheem]
    I've seen and worked on these....91 can seem very cool blowing over your bare hand too. But it heated the house just fine....

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,916
    On the old one, you are likely running less than 400 CFM/ton if the duct static pressure is high.

    The VS should, within reason, keep the airflow up to the setpoint, even if static is above normal.

    We only service a couple of twin compressor pumps but neither one of them seems to give much of a temp rise.

    I wonder if your upstairs unit has a scroll, I find they tend to do better than the big orange recips too.

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