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VFD controller for multi stage rooftop units

There was a company that made a vfd and controller that can be retrofitted into a constant volume multi stage rooftop unit in order to reduce the speed of the fan when only one compressor is running. Does anyone know the name of the company? I think these would be best used in belt driven applications so there is better humidity removal, and comfort to have the fan slow down, as the heat load in the space is reduced. If anyone knows the name of this company, please post. We used one about eight years ago, and their controller was easily interfaced with the rooftop unit's circuit board. I just can't remember where we purchased it. thanks to all


  • ratio
    ratio Member Posts: 3,654
    That doesn't sound too hard to do, without any kind of controller. Every VFD I've seen has several inputs that can be configured for different speeds. Just use a few relays to shift into high when Y2 or any of the W's are energized.

    If you wanted to be clever (I do!), I'd drop a thermistor in the supply & let the VFD manage speed to reach a target DAT, too.