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  1. #1
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    Non-Balancer question for a Controls Guy

    Dumb question about Balancing a Change Over-Bypass (COB) system. The system has a constant speed fan for cooling and a somewhat reduced speed for heating, i think.

    Can I get the Readers Digest explanation (Thumbnail) of how a COB gets balanced ?

    My understanding is that the motorized Zone Dampers have to be fully open and then the registers/Diffusers need to be measured and set (cut at the takeoff's) to Max design Flow. Then the total Flow of the RTU has to be adjusted, maybe, to match the total flow requirement, right ?????

    I believe then, and only then, can the Flow bypass get setup to open based on Total Static pressure.

    Please correct my ignorance on this.

    Thanks in advance.
    If sense were so common everyone would have it !
    Stupid should Hurt !
    If people took care of their cars like they do their HVAC Systems you'd see a lot more people walking
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  2. #2
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    Are you going to bring in a balance contractor? If not do you have the test equipment to balance the system? These systems are a pain to balance. The bypass should be controlled by supply duct static not total static. It has to be balanced in the max cooling mode in order to know the required static pressure set point and that depends on where the sensor is located. I've seen a lot of sensors located at the fan discharge.

  3. #3
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    Thread Starter
    WAYNE3298,
    Odd situation. The Balance contractor has done his stuff, correctly I believe. Now we have an equipment guy telling us that the balance is not correct and changing stuff (D'oh !).

    I have talked to 2 of my local Balancing experts and I am leaning towards the equipment guy not quite understanding how a COB system actually has to work.

    I am just going to step back and wait to see how this all turns out.

    Thanks for your reply, though.
    If sense were so common everyone would have it !
    Stupid should Hurt !
    If people took care of their cars like they do their HVAC Systems you'd see a lot more people walking
    !

  4. #4
    Join Date
    Feb 2016
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    If you work for the owner demand a meeting with all parties and make the equipment guy explain what is wrong and what needs done. If the balancer did his job the equipment guy will look stupid. What is wrong that he is screwing with it?
    The purpose of the bypass is to maintain the manufacturer's required minimum airflow across the coil and that is done by adjusting the maximum static pressure required to deliver design airflow to all the units served.

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