Commercial kitchen exhaust fan

[mkgrady]

In this golf course restaurant they have an exhaust fan over the stove tops and fryer. The fan runs real hard and loud yet it doesn't cool the room down much. At the same time they complain that the unit sucks the air conditioned (cooled) air from the dining room which they consider more of a problem than the hot kitchen.

I have asked if it is possible to put a speed control on the fan motor. I suspect the real problem here is that there is no makeup air duct to the kitchen. I will suggest they get the makeup air installed which should solve both problems but I still wonder is there any reason the fan speed can't be made adjustable?

 

[Smart $]

...but I still wonder is there any reason the fan speed can't be made adjustable?

Fire marshal approval?

 

[mgookin]

Get a mechanical engineer before you go messing with that system. You can have variable speed hood fans but there has to be sensors to make it happen automatically. The first thing to look at is an air inlet which it sounds like you're lacking. Once a mechanical engineer draws up a cure plan you can do the electrical install.

If they don't want to hire the mechanical engineer, somebody needs to dig into the mechanical code and ASHRAE documents.

 

[ActionDave]

I have asked if it is possible to put a speed control on the fan motor. I suspect the real problem here is that there is no makeup air duct to the kitchen. I will suggest they get the makeup air installed which should solve both problems but I still wonder is there any reason the fan speed can't be made adjustable?

Need makeup air for sure.

Does the fan have the original motor in it, or one that is the correct RPM? Some times a fan motor will get changed to one that has a higher RPM because someone thinks it will it draw better. It just ends up making it louder. Bad bearings, loose belt, bad pulley can cause some racket too.

Adjusting the speed on a basic restaurant exhaust fan is usually not a good idea. Likely it is a single phase motor with a starting switch and slowing it down will ruin the motor. If it happens to be a permanent split motor it may need a certain amount of air flow to stay cool enough to not trip the thermal.

 

[Wenty4]

commercial kitchen exhaust fan

commercial kitchen exhaust fan

If and when you install make up air it will have to be conditioned to within 10 degrees F of interior air temperature (IMC 508.1.1). Also the amount of make up air must equal the amount of exhaust air, so if you adjust one the other must be equally adjusted

 

[HoosierSparky]

In this golf course restaurant they have an exhaust fan over the stove tops and fryer. The fan runs real hard and loud yet it doesn't cool the room down much. At the same time they complain that the unit sucks the air conditioned (cooled) air from the dining room which they consider more of a problem than the hot kitchen.

I have asked if it is possible to put a speed control on the fan motor. I suspect the real problem here is that there is no makeup air duct to the kitchen. I will suggest they get the makeup air installed which should solve both problems but I still wonder is there any reason the fan speed can't be made adjustable?

Per the 2012 IMC:


507.13.1 Extra-heavy-duty cooking appliances.
The minimum net airflow for hoods, as determined by Section 507.2, used for extra-heavy-duty cooking appliances shall be determined as follows:

Type of Hood CFM per linear foot of hood
Backshelf/pass-over Not allowed
Double island canopy
(per side) 550
Eyebrow Not allowed
Single island canopy 700
Wall-mounted canopy 550

You, as the EC, do not want the responsibility of determining the exhaust rates. Usually this is a designed, reviewed, installed and inspected SYSTEM. You can change out motors, but have to maintain the rpm's.

Makeup air should have been supplied. I'd check to see if THAT fan is working. It is supposed to kick on when the exhaust fan starts, so look for a sticky relay. K.I.S.S!

 

[mkgrady]

Per the 2012 IMC:


507.13.1 Extra-heavy-duty cooking appliances.
The minimum net airflow for hoods, as determined by Section 507.2, used for extra-heavy-duty cooking appliances shall be determined as follows:

Type of Hood CFM per linear foot of hood
Backshelf/pass-over Not allowed
Double island canopy
(per side) 550
Eyebrow Not allowed
Single island canopy 700
Wall-mounted canopy 550

Thanks for this and all the other replies. Very helpful. I plan to have t
You, as the EC, do not want the responsibility of determining the exhaust rates. Usually this is a designed, reviewed, installed and inspected SYSTEM. You can change out motors, but have to maintain the rpm's.

Makeup air should have been supplied. I'd check to see if THAT fan is working. It is supposed to kick on when the exhaust fan starts, so look for a sticky relay. K.I.S.S!

Thanks for this and all the other replies. Very helpful. I plan to have them contact an HVAC contractor.

 

[PetrosA]

This thread reminds me of a job I did last year. Resi, with a 48" Wolf range, and a 1200 CFM exhaust. Luckily all I installed was power to the hood. Someone else is responsible for the fact that the exhaust duct is undersized, there's no make-up air (let alone conditioned...) and the hood fails its self calibration mode. In spite of those issues, it blew a potted tree over on the deck where it's vented out to.

It's another example of someone designing and selling a system who shouldn't be doing that.

 

[kwired]

Outside of following requirements... no make up air means it will try to pull air in through any opening it can, this can cause backdrafting of gas appliances, may make the front door difficult to open until the "seal is broke" then it will open easier, and if there is not enough "make up air" leakage the fan will not draw the amount of air it was maybe intended to draw either making the unit appear as though it maybe is undersized.