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Make up air

M

Marshal Chris

Silver Member
Joined
Oct 23, 2009
Messages
155
Location
Long Island, NY
NYS Version:

508.1.1 Makeup air temperature. The temperature differential between makeup air and the air in the conditioned space shall not exceed 10°F (6°C).

Exceptions:

1. Makeup air that is part of the air-conditioning system.

2. Makeup air that does not decrease the comfort conditions of the occupied space

*********************************************************************

So, do you require make up air to be tempered? Who determines "comfort conditions"?

Anyone with commentary from the mechanical code shed some light on what it says?
 
The intent is to prevent the makeup air from causing employee discomfort. The 2006 IMC Commentary says that makeup air being supplied through the air-conditioning system does not have to comply with the temperature limitation.
 
I am going to take a shot at your question being directed to a make up air unit for a commercial hood in a restaurant setting. Colder climate areas do need to have the make up air for the hoods to be tempered to the 70 degree range. The make up air in the dining area is done through the economizer using enthalpy controls to determine outside air and relative humidity to modulate the economizer open or closed to maintain thermostat setting.
 
I'm talking about dedicated makeup air not part of HVAC for the area. Dedicated unit with grills on the front of the hood providing make up air. Is that supposed to be temperature regulated? If the owner tries to state that it will not decrease comfort, how do we dispute that?
 
Marshal Chris said:
I'm talking about dedicated makeup air not part of HVAC for the area. Dedicated unit with grills on the front of the hood providing make up air. Is that supposed to be temperature regulated? If the owner tries to state that it will not decrease comfort, how do we dispute that?
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If the unit is self contained, part of the hood with grills on the front or inner rim are "compensating hoods and air tempering is not required. The air travels a short distance and is pulled back through the hood as exhaust.

If the makeup air was being supplied through through grills through the ceiling or wall registers it would need to be tempered to within 10 degrees of the design temperature of the space.

The reasoning behind the tempering is for the comfort and safety of the workers. If the make up air was entering the space at 40 degrees or lower the systems have been known to be shut down allowing for a negative pressure to be created and causing high levels of CO and smoke build up leading to major issues.
 
This picture is taken from http://www.kitchen-hoods.com. Only thing I could find that was close to the installation I am thinking of. The unit has an upblast fan and 10 feet away is the make up air unit that provides air to the space. The grills are not open into the hood, only the outside. ??

View attachment 520

View attachment 520

/monthly_2012_01/kitchen-hood-1-a.jpg.9cb5f15eeda177fe2f3e4294b57ab975.jpg
 
Yes.

No, the "mushroom exhaust" is an "up-blast fan". A down-draft fan looks like a mushroom. The down draft fan blows the grease onto the roof, increasing problems when the exhaust ssytem catches fire. Down draft fan are not allowed in new installs.

Yes. Make up air can be a swamp cooler or conditioned air

http://www.captiveaire.com/ http://www.greenheck.com/products/category/6

Both sites have lots of good info about Type I and Type II exhaust systems. Both companies also have seminars and want you to attend and get educated.
 
That is not a compensating hood. A compensating hood has the make up air outlets inside the hood enclosure, such that the make up air never enters the room, and therefore, the theory goes, it does not need to be tempered. Compensating hoods do not work very well or very reliable, especially with particularly greasy air, or wide swings in outside air temperature.

With the make up air grilles on the face of the hood, the air enters the room before it gets sucked up the hood, and therefore will affect the thermal comfort in the room. Under certain conditions, it can improve thermal condtions, providing a cooling effect to the cooks, but if the air is too cold, make up air unit gets turned off.

If the owner tries to state that it will not decrease comfort, how do we dispute that?
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Logic. How can blowing -5 degree air 1 foot over a persons head NOT decrease comfort. Perhaps withhold a CO until a test can be run on a design day.
 
providing a cooling effect to the cooks, but if the air is too cold, make up air unit gets turned off.
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Or the kitchen staff wind up coughing and sneezzing all over the food and prep areas because of the constant colds they have through the winter months.
 
Well, I'm in agreement it needs to be tempered. Unfortunately, I was looking for more concrete info. My supervisor is of the opinion that the statement "2. Makeup air that does not decrease the comfort conditions of the occupied space" is the "out" a business can use to not require tempered air. I've tried the logic approach you've suggested Dr. J, but the statement "why would they put that in there or not take it out if it's not applicable (I'm in ny, talking about ny enhancements).

I said that it's a national code and tempered air wouldn't be required in Cali, AZ and the like where the temperature won't cause a difference in temperature.

This is my dilemma.
 
We have had a great number of resturants built in the last 5 years or so (for a 50k town that is) - and I've researched this issue at length. A few thoughts to throw into the mix:

1. Dr J - all respect here - but I have to disagree. That is indeed a compensating hood. It is NOT a short circuit hood.

2. Any system that pumps the air into employee work areas in the kitchen, that does not go through the HVAC system, should be tempered. We have enough history around here with the make up air being closed off (cardboard and duct tape is pretty popular) that we have all the justification we need. The cooks really do not like sub-zero air droping in on their necks. In really warm climates - the make up air may need to be cooled!

3. Short circuit hoods (make up air dumped into the containment area of the hood) do not HAVE to be tempered, but should. As Dr. J mentioned, temperature swings cuase problems under the hood.

4. Short circuit hoods are becomming less and less popular (at least around these parts), as the testing has shown that to obtain proper contaiment, the system has to be blanced precisely. The latest report I read showed that a very slight change in the CFM of makeup resulted in spill over of effluent. The PEs I"ve talked to tell me they are very uncomfortable designing a short circuit system.

5.All that said (written) we allow non-tempered compensating hoods of two designs - short circuit, and back wall plenum. By far the most popular now is back wall plenum. The air comes in cold at times, but its at floor level, under the hot surfaces, and doesn't seem to be a problem.
 
I was going to claim regional differences in terminology between compensating and short circuit, but the IMC defines compensating to include short circuit as one type of compensating hood:


COMPENSATING HOODS.

Compensating hoods are thosehaving integral (built-in) makeup air supply. The makeup air

​
supply for such hoods is generally supplied from: short-circuitflow from inside the hood, air curtain flow from the bottom ofthe front face, and front face discharge from the outside frontwall of the hood. The compensating makeup airflow can alsobe supplied from the rear or side of the hood, or the rear, front orsides of the cooking equipment. The makeup airflowcan be one

​
or a combination of methods.



I stand corrected. Replace "compensating" with "short circuit" in my post above. I concur with all of Darren's comments. I have refered to the link he provided many times.
 
Marshal, look at IBC 1204 Chapter 12 "Interior Environment" section 1204 Temperature Control 1204.1

In your geographical location with ambient winter design heating days from -1 degree Fahrenheit to 15 degrees F the air should be tempered to within 10 degrees 68 degrees being the minimum for comfot level in space.
 
Gregg Harris said:
Marshal, look at IBC 1204 Chapter 12 "Interior Environment" section 1204 Temperature Control 1204.1 In your geographical location with ambient winter design heating days from -1 degree Fahrenheit to 15 degrees F the air should be tempered to within 10 degrees 68 degrees being the minimum for comfot level in space.
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I would only point out a few things from my experience. First, I would allow a 60 degree supply temperature, due to the fact that kitchens are almost always too hot. Second, allowing untempered air, even on a short circuit or back area supply, can cause the chef no end of head aches because he never knows how his cooking surfaces are going to react to the hot or cold air blowing across or below them.
 
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