Exhaust Fan and Actuator

[Hamdog]

We just replaced an existing dishwasher exhaust fan (utility set) with an uplast 2500CFM at 3.5" ESP. We installed a motor operated damper in the curb adapter so when the fan starts up the damper opens up. This was an internal mounted fast acting actuator 120V. Since the owner wanted to use existing electrical and not run any new circuits (cost), we pulled 480/3/60 from the disconnect to a transformer (Nema 4) and then 120V from the transformer to actuator. The owner wants the actuator on the curb exterior, not a big deal find an actuator with nema 4 enclosure. Well I cannot find a Nema actuator that is fast acting, the quickest is a 75s run time. Now besides ordering the actuator with an auxillary switch and putting in a relay prior to the fan starter so when they turn on the fan it will not start till damper is open.

Anyways would it be fine if I use a 75s run time actuator? So when fan turns on the actuator starts opening the damper. Will this "hurt" the fan or motor? The factory initially sent it with a 25s fast acting actuator with no auxillary. Thanks!

 

[MintJulep]

Probably won't hurt anything.

Might be noisy as heck when the damper first cracks open.

 

[berkshire]

Why do you need a motorized damper in the first place?
Are you trying to avoid wind rattle from airblast/gravity operated dampers?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Hamdog]

We are trying to reduce the system static pressure. What happened the engineer who designed the system designed for half the CFM required. After the building was commissioned and the dishwasher had been running for a while they realized that the engineer sized the system for not enough CFM. So in order to get the CFM needed in the size duct that was installed the static pressure is around 3.5" so in order to use an upblast fan (owner request) we had to do everything we could to reduce the system static pressure without removing duct in the building. So we chose not to use a BDD. It would have been the easiest solution but would not been able to get the performance we needed out of the fan. The fan is running great and at the CFM needed. The damper is wired opened until we get a new actuator. Thanks!

 

[willard3]

Have you checked the pressure drop of a backdraft damper vs the motorized damper? I did a quick check and those I checked are about the same.

Backdraft damper has the advantage of not failing so often as a motorized damper, especially in a wet environment, nema 4 enclosure or not.

 

[Hamdog]

The size duct we have the damper in there is min pressure drop as opposed to the BDD. I do not recall what the difference was but significant enough. Normally we just install BDD that is what was on the existing fan, but for this case a MOD was used. Thanks!

 

[simsd]

I need your in/lbs for the actuator and I can help you. You may or may not like my solutions but I have a few as we ran into this problem this year with a highly corrosive application (water treatment plant beside the ocean).

I also took pictures of what we did so I can send them to you.

 

[KiwiMace]

Put in a goose neck instead.