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Add VFD to 20 ton AHU


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Add VFD to 20 ton AHU

Hey guys - It's me again... [:-bigeyes

I am working on a portfolio of commercial buildings (various ages and sizes) where they are adding VFDs to many AHU's as part of a Johnson Controls retrofit and then adding Logic controllers to control the pneumatics of the field VAVs and Powered Induction Units.

I have heard a lot of discussion about if this is advantageous or not because of pressures and flooding of coils, etc...

I know they are doing it. I am thinking it may be a good idea for me to start recommending it where they have not done it yet.

Is this a good idea or not?

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  • 2 weeks later...

I am a quick learner. What I am looking for is information. Having a hard time finding it. Most places have field VAV's and PIUs with pneumatic controls. Johnson Controls handles most people in the area and in most cases (for these clients), they use JCI for most buildings and are adding VFD's to the supply and return fans over 25 hp.

I was trying to find out where people see problems with this. Most clients think it is great and are doing it and pretty sold on it - more-so than I.

I guess the crux is - what are the primary control (and other) issues that are overlooked in this situation?

Thank you again for all of your help.

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I've heard of significant savings by adding VFDs to pumps for pipelines. I'm supposing that the advantage is to maintain torque while being capable of varying the speed. Within a facility the situation is different; the addition of VFDs might require isolation transformers & K-rated transformers to prevent harmonics from coming back into the power system. These could add to the installation cost, and their energy losses could partially offset the savings of the VFDs. I suggest consulting a qualified power quality engineer.

Douglas Hansen

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