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Ducted heat pump and air handler behaviour

retdinbc | Posted in Mechanicals on

We had a ducted heat pump and air handler installed last Spring to replace an existing FA gas furnace heating system. To date, the system appears to be working well at managing the cooling and heating of our home, however we noticed immediately that the air handler fan appears to run continuously (24/7) even when the room temperature shown on the thermostat matches the set temperature. Is this normal behaviour for ducted heat pump systems? This seems to use energy for the fan when it’s not required and could also result in long-term wear on the fan bearings, etc.

Our old FA furnace fan would come on and off with the burner to maintain the thermostat setting. An energy advisor firm provided a Canadian EnerGuide rating for our insulated 1929 Vancouver BC (Zone 4?) house at 56 GJ/year with 5.1 air changes / hour. The heat pump system installed is a Mitsubishi PUZ-HA24NHA1 outdoor unit, a Mitsubishi PVA-A24AA7 indoor unit, with a Mitsubishi PAR-40MAAU remote controller replacing the furnace thermostat at the same location in the house. Since I’m new to heat pumps I don’t know what the expected behaviour should be.  Any advice is appreciated.

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Replies

  1. retdinbc | | #1

    As I posted this question, a link to a related (identical) question with the answer was provided here:
    https://www.greenbuildingadvisor.com/question/mitsubishi-pva-air-handler
    So no replies required, thanks, will use a better search strategy next time!
    Gary

  2. walta100 | | #2

    Consider this heat pump has a variable speed compressor.

    The compressors speed is deduced when it gets close to the set point and increased when it gets away from the set point. The only time the unit should reach the set point is when the outdoor temp is close to the set point and the compressor’s minimum speed will overshoot the set point. Only then does it cycle on and off the way your old equipment worked. It will be normal for this equipment to be running 24-7 for months at a time.

    Yes the new fan will run more hours than the old fan did but the new fan uses less power and every startup is hard on the equipment and requires considerable energy.

    I think you will find the new equipment will use less energy and keep the room much closer to the set point than the old equipment did.

    Walta

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