"Auto" or "On" fan with ERV/HRV ?
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  1. #1
    Join Date
    May 2004
    Posts
    58
    The heat pump's ductwork is in the attic - taped, and insulated (no large leaks). The HRV/ERV setup is one of dedicated return in common area (this 6" rigid return is run in conditioned space only) , and HRV/ERV fresh supply tied to the Fan Coils (Bryant FE4) main supply trunk.

    1)With this type of set up would the fancoil blower need to
    be running ?

    2)What is the major problem with running a fan coil blower
    continous low ?,
    3)I read on the "Puretech" thread that running the blower
    on continous causes mold ? how ?

    Thanks,
    Nick

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,231
    Originally posted by nicholasa
    The heat pump's ductwork is in the attic - taped, and insulated (no large leaks). The HRV/ERV setup is one of dedicated return in common area (this 6" rigid return is run in conditioned space only) , and HRV/ERV fresh supply tied to the Fan Coils (Bryant FE4) main supply trunk.

    1)With this type of set up would the fancoil blower need to
    be running ?

    2)What is the major problem with running a fan coil blower
    continous low ?,
    3)I read on the "Puretech" thread that running the blower
    on continous causes mold ? how ?

    Thanks,
    Nick
    No problem operating the fan continously during the non-cooling season. Operating the fan during the a/c operation re-evaporates any moisture on the a/c coil at the end of the cooling cycle. This is 4-7 lbs. of moisture per off cycle. The evaporation elevates the indoor humidity as it dries the coil and ducts. As the indoor humidity levels rises, the a/c removes more moisture. The net effect is a a more humid house with drier coil/ducts. All things considered, do not operate the fan continously if the indoor humidity is +50%RH.

  3. #3
    Join Date
    Jul 2001
    Location
    Central MN and the Twin Cities
    Posts
    1,530
    Her we have to interlock our HRV's with the blower motors so that the HRV turns on the blower when it runs. If the air exchanger is tied into the main ductwork then you want the furnace/airhandler blower running with the HRV. If you do not want it to run all the time then get them to "interlock" them. They make kits for this.
    Warning: Just because I am over the head injury doesn't mean I'm normal!

    The day I stop learning.... I'm dead!

  4. #4
    Join Date
    May 2004
    Posts
    58
    Grasshopper,
    how are You ducting the your HRV's ?
    If both the fresh air and stale air is plumbed into the main trunk (of the Air handler), then yes the air handler's fan must run for the HRV to work.

    In this case there is a dedicated return for the HRV, and the fresh air supply will be tied to the Air handler's supply trunk. Without interlocking the air handler's fan, would the fresh air cycle out the supply closest to the HRV return ?

    Nick

  5. #5
    Join Date
    Jul 2001
    Location
    Central MN and the Twin Cities
    Posts
    1,530
    Nick- here in our state they require that anytime the HRV and the furnace share ductwork that the two be interlocked. I would suspect that it is in part to that the fan on the HRV only moves a fraction of the air that the furnace does and will not apply the proper preasure on the ductwork to deliver it. We duct our HRV's depending on the job. In new construction we often have seperate duct system just for the HRV. In retro fit we go into the existing ductwork.
    Warning: Just because I am over the head injury doesn't mean I'm normal!

    The day I stop learning.... I'm dead!

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