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Thread: VRV control

  1. #1
    Join Date
    Jan 2011
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    72

    VRV control

    We are tendering a small job with VRV. 7 in ceiling fan coil units, each one serves a single zone.

    Here is what the engineer specified:

    1.The zone supply air shall modulate to control the zone space temperature. The supply air temperature shall be constant.
    2. If the internal space temperature drops below the set point, reset the supply air temperature.

    Is that a common control method of DX systems? I am confused how to control it with the above specification.
    My understanding is, when the space temp reaches the setpoint, the compressor will unload, and there will be no refrigerant circulating the evaporator in this fan coil unit. Since the space temp will not drop below the setpoint, how to reset the supply air temperature? Also how to modulate the supply air? using volume control damper? They are all single speed fan without VFD.

  2. #2
    Join Date
    Apr 2010
    Location
    southern california
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    535
    What brand of VRV are you using. The system will modulate the refrigerant flow to the air handlers ramping up and down the capacity of each zone by changing the the speed of the inverter compressor in the outdoor unit. The engineer specs are worded a little differently but his first note A VRV will modulate to control the space temp by modulating the refrigerant flow. Note 2 I believe what he is trying to say is that after the zone has satified itself and as the space temp. has a demand for cooling or heating, the unit will ramp itself back up to meet the requirement of the space. VRV need special controls which are part of the package. If you have no experience with these systems , I would strongly recommend taking a training course by the mfg.before attempting to install a system. There are a lot of mistakes which can be made,and the equipment is expensive.

  3. #3
    Join Date
    Jan 2011
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    72
    VRV manufacturer is not specified.

    No matter what brand it is, all VRV controls shall be in the whole package, right?

  4. #4
    Join Date
    Apr 2010
    Location
    southern california
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    535
    Yes, the engineer should specify the control options. If you are bidding on this project be aware of the time to commission equipment.

  5. #5
    Join Date
    Jan 2003
    Location
    USA
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    1,685
    All the VRVs I have seen come with factory controls.

    The only things you have to worry about are miscellaneous parts and pieces that the factory controls may not be able to deal with.

    Such as:

    External OA / relief dampers
    External HW / Electric heat like fin tube, etc

    You will want to make sure the OEM controls meet the sequence that the ME has spelled out. If they come with controls you don’t have much flex in how they operate.
    Propagating the formula. http://www.noagendashow.com/

  6. #6
    Join Date
    Jan 2011
    Posts
    72
    According to the specification, modulating dampers are required to control the supply air volume for fan coil units, which I think is not necessary in VRV system.

    The VRV is cooling only. There will be gas furnaces taking care of heating. Seems like only OA dampers needs to be controlled.

  7. #7
    Join Date
    Jan 2003
    Location
    USA
    Posts
    1,685
    And something to prevent the VRVs from fighting the furnaces...
    Propagating the formula. http://www.noagendashow.com/

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