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Thread: make-up and exhaust help
11-29-2006, 07:42 PM #1
This morning I had a call at a new restaurant that we installed the RTU's on. The call was the restaurant was filling up with smoke the previous day when they were test running the grill. So I arrive this morning and check the exhaust hood only pulling 3.2A motor rated at something like 5.4-6.0A FLA. I spun the drive pulley all the way closed and then backed it out one turn and got the motor to pull 4.6A. Checked the make-up air unit pulling close to FLA. Made sure they were both spinning in the right direction--they were. Then I noticed 2 of the RTU,s our company installed did not have fresh air on them. Thought maybe they were inside the 10' perimeter of the exhaust--nope. Go get fresh air vents (manual) and install them. I set all three fresh air vents at 50% dont remember the exact dimensions. Go back down in the kitchen and they were starting to cook chicken--perfect--now I can see if the exhaust is doing a better job--pulling smoke out great. Later that day get a call-back kitchen was full of smoke again--Service Manager took the call. Asked him what the problem was and he said when he got there the smoke had already cleared out but he went ahead and spun the pulley down that last turn and got the motor to pull 5A. I still don't think this will help--guess we'll find out tomorrow. I am an ac tech and don't have really any experience with this. The building seemed to be slightly positive when I left. Any input would be greatly appreciated on this. The RTU's are Lennox--2-4 ton units and one 5 ton. M/N-CHA16-060-1P and the 4 tons are both M/N-CHA16-048-1P. The make up air is supplying 1400 cfm and the exhaust is rated at 1750 cfm.
11-29-2006, 09:52 PM #2
call melink ... they balance alot of buildings .. only thing i can say
11-30-2006, 09:10 AM #3Regular Guest
- Join Date
- Jun 2006
i kinda had the same problem, but mine had to do with the make air not on, see the desighn was that the make air came in at the rear of the stoves ,grills, and the cooks would end up getting hit with all that heat,so thay would turned the make-air off, well that made the exhust fan work extra hard pulling at a higher amp thus over amping the motor, look at the disghn, good luck.
11-30-2006, 12:06 PM #4
1700 Cfm is NOT much exhaust air at all. Must be a very small hood. If it is not a pre-engineered system that is about right for a 4' exh hood. Where does the MUA supply to??? If it an internally compensated hood, the air is diluted and you don't get the full benefit of exhaust. How large is the hood and what is under it. Maybe a bad engineering job from the get go.If you really know how it works, you have an execellent chance of fixin' er up!
Tomorrow is promised to no one...
11-30-2006, 01:02 PM #5Professional Member
- Join Date
- May 2000
Most air balance mistakes in restaurants are made by someone setting the exhaust to FLA. That's not the way it works. If you will bear with me.
MOAD's on the AC units should be set near 20 - 30% depending on the fan operation. Constant fan on will give you constant air balance requirements. Fans set to cycle will give you in a headache when working on building balance. Lock the fans on constant on if you are allowed.
Next, check all duct work for leaks above the drop ceiling, fix any leaks and set all dampers to 100% open. Yes, you can adjust for comfort areas that may blow on customers.
Next, set the make up air fan and exhaust to 50% and check for positive or negative pressure in the building. If there is a drive thru window, try to keep it closed.
When standing at the front door, open it. If there is air that pulls you in, you are negative and the hoods will not pull smoke. If it pushes you out or hits you in the face when entering the building, you are in a positive pressure.
Positive pressure is what you are looking for but just slight positive. If too positive, adjust your MOAD first by closing just a bit. If that does it and you still have a slight positive air effect you're done.
If you have too much of a positive effect still then increase the exhaust fan to compensate but do not run the exhaust fan more than 80%. After that you must use the make up air fan to adjust your flow. You must compensate by putting air in, not pulling air out.
I hope this makes sense.
[Edited by david on 11-30-2006 at 01:12 PM]
11-30-2006, 05:59 PM #6
Thanks Guys For All The Input !!!
I really appreciate all the help. The Boss went and looked at it this morning and found a problem with the duct going up to the exhaust fan--I think he said the duct was only under half of the exhaust?.?. So they are going back tomorrow to correct the problem. I will keep you updated on this issue. Thank-you again for all of the help and input.
12-17-2006, 09:32 PM #7
Just got called back to the franchise--kitchen filling up with smoke again. I watched them put 4 burgers on the grill and smoke was just rolling out of the sides of the hood. I go up on the roof and it looks like a forest fire-smoke was coming out of the exhaust pretty good. My question is do you think a Captiveaire 4530 ND is to small for what they are trying to do? This franchise is the Steak Out and all of their food is prepared on the grill. Any input would be greatly appreciated. I don't really know anything about Comm. Food service equipment.
12-18-2006, 12:01 AM #8Professional Member
- Join Date
- Aug 2002
- manitowoc wisconsin
Internally compensated hood?open the makeups on the rtu's & slow the mua in the hood down but keep that positive pressure.13 tons is not alot of heating & cooling it must be a small place.Bring as much air as you can in externally from the hood.Take your time & do it right!
12-18-2006, 11:09 AM #9
I took a tour of Greenheck's manufacturing facilities back in 2002, a first class operation. They have a demonstration kitchen with a disco smoke manifold along the cookline which allows you to see the capture of fumes as well as what happens when various problems cause the hood to spill. Interesting watching the smoke. Anyways some basic information on kitchen ventilation is available at http://www.greenheck.com/products/ki...tion_guide.phpThe way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.