HVAC Question for Paul

[_Markk]

Have you ever heard of a VFD on a single phase exhaust fan (for commercial kitchen hood)? I have a kitchen sub (owners sub) telling me it is possible but our electrician and HVAC sub say he is nuts, that it has to be a 3 phase motor. I have the question into the engineers.

The problem, in short, is the mechanical plans called for both single phase and 3 phase fans (which are installed), but the electrical plans called for single phase home runs to all disconnects, but the controls call for it going through a VFD system to all fans(installed by others and not on the plans), and no one said anything until we are done with the project.

The electrician, in good faith, trying to fix it ran a 3 phase home run to a three phase fan through the same existing conduit as the single phase home runs...but the hertz from the single phase lines are confusing the VFD of the 3 phase motor, and the motor shuts on and off instead of slowing up and down when it get hot or cool at the exhaust hood.

Also, I had the electrician, on his suggestion, by pass the VFDs (called for the single phase motors) and put on contacts, which worked, but voided the fans warranty according to the kitchen equipment manufacture, becasue they start too hard...it is a mess, and holding up last payment.

I don't know who to believe. The irony is that I told the architect we would hook up the controls "as a favor" and it is biting us in the rear and holding up around 500K in retention. It always seems being a nice guy never works in construction.

[_Jersey Girl]

Markkkkk I don't think he looks down here much. I think your messages are broken. I'll send him a little pm for you to heads up him about the OP.

[_Markk]

Markkkkk I don't think he looks down here much. I think your messages are broken. I'll send him a little pm for you to heads up him about the OP.

I have no idea why my messages won't work...I have asked Shades a couple of time to look at it...but o'well.

Thanks

[_Xenophon]

I have no idea why my messages won't work...I have asked Shades a couple of time to look at it...but o'well.

Thanks

You may have already done so, but there is an option you can check in your "User CP":

[_Jersey Girl]

No problem Markkkkk Jersey Boy is also HVAC but he's not here right now and Paul is your best bet for current advice/trouble shooting. I did send him a little message. I'm sure he'll pop in eventually. Really cool that we have resource folks for various topics on this board. Good luck!

[_Shulem]

Have you ever heard of a VFD on a single phase exhaust fan (for commercial kitchen hood)? I have a kitchen sub (owners sub) telling me it is possible but our electrician and HVAC sub say he is nuts, that it has to be a 3 phase motor. I have the question into the engineers.

The problem, in short, is the mechanical plans called for both single phase and 3 phase fans (which are installed), but the electrical plans called for single phase home runs to all disconnects, but the controls call for it going through a VFD system to all fans(installed by others and not on the plans), and no one said anything until we are done with the project.

The electrician, in good faith, trying to fix it ran a 3 phase home run to a three phase fan through the same existing conduit as the single phase home runs...but the hertz from the single phase lines are confusing the VFD of the 3 phase motor, and the motor shuts on and off instead of slowing up and down when it get hot or cool at the exhaust hood.

Also, I had the electrician, on his suggestion, by pass the VFDs (called for the single phase motors) and put on contacts, which worked, but voided the fans warranty according to the kitchen equipment manufacture, becasue they start too hard...it is a mess, and holding up last payment.

I don't know who to believe. The irony is that I told the architect we would hook up the controls "as a favor" and it is biting us in the rear and holding up around 500K in retention. It always seems being a nice guy never works in construction.

Any commercial application I've ever dealt with involving variable frequency drives always utilizes 3 phase dedicated power sources -- usually 480 VAC. I've never encountered or heard of any commercial kitchen equipment fans using VFD's because kitchen equipment vent hoods and screens need lots of air volume, hence a constant volume produced from a blower wheel designed to pull a rated amount of CFM. Starts and stops are quite minimal because you basically turn the fan on at the beginning of the day and off when you're over. No need for a soft start from the VFD because the belts are only hard started once per day. VFD's on commercial kitchen hoods is the most stupidest damned idea I've ever heard of. It's beyond retarded -- it's insane. Whoever came up with that idea and is selling those products should be shot. Good god, it doesn't require rocket science to vent out nasty dirty air. Turn the damned blower on and let it rip. “F” trying to find the right speed. A properly sized vent hood is going to do its job and more. Better to ventilate more than not enough!

I would think that in order to avoid possible electrical cross talk or interference in electrical frequency that any and all power sources for VFD motors should be run through dedicated conduit having a dedicated power source via the bus panel disconnect -- hence isolation is key.

Regarding those fan motors wherein the warranty mandates the use of VFD's rather than contactors or conventional motor starters that sounds like a load of crap. If the motor runs continuous with infrequent cycling there shouldn't be any problem with the motor and the belts (if used) can certainly handle it. It's a goddamn damned motor! They are meant to turn on and off and so long as you're not constantly cycling them the motor windings should remain relatively cool.

[_Shulem]

Are we allowed to say "“F”" down here in paradise land?

I'm used to saying "“F”", I say it all the time in real life.

[_Nomomo]

Single Phase VFD's are rare, but real.
https://www.google.com/search?q=single+phase+vfd

[_Markk]

I finally got the real story. The make up air and exhaust fan manufacture has two divisions, one for equipment and one for controls...they did not communicate with each other and the controller was designed for 3 phase VFD's while the MUA and 4 of 5 of the exhaust fans were designed for simple single phase operation with relay/contact control. The controller had three VFD's yet only one exhaust fan was three phase and compatible with the control panel. In the end it is their screw up and they have to redo the equipment to compliment the controls.

[_Shulem]

I finally got the real story. The make up air and exhaust fan manufacture has two divisions, one for equipment and one for controls...they did not communicate with each other and the controller was designed for 3 phase VFD's while the MUA and 4 of 5 of the exhaust fans were designed for simple single phase operation with relay/contact control. The controller had three VFD's yet only one exhaust fan was three phase and compatible with the control panel. In the end it is their screw up and they have to redo the equipment to compliment the controls.

Glad you got it taken care of.

Enjoy this temple flick while listening to the beat:

Mormon temple film

creepy