return air in commerc ial kitchen

[BSSTG]

Greetings all,

While looking at a kitchen hood on a remodel job I noticed 2 branc new AHU's in a closet just off of the kitchen in a closet. Red flag went up as I was unaware of any permit or new ac system going in. What looks problematic is the return air for these units is drawn from the kitchen. The heaters are electric so at least there is no gas involved. I'm trying to find in the IMC a restriction for return air in the kitchen. It may not be an issue if the units are for the kitchen only but I have my doubts on that.

Thoughts?

thanks

BS

 

[Dr. J]

What code?

If 2006: Since this has a heater in it, it can be classified as a "Forced-Air Warm-Air Furnace", and 918.6 applies: "918.6 Prohibited sources.

Outdoor or return air for a forced-air heating system shall not be taken from the following locations:...5. A closet, bathroom, toilet room, kitchen, garage, mechanical room, boiler room or furnace room.

Note however, this prohibits all return air, not just recirculating air to other spaces. Thus one can't even recirculate air back to the kitchen.

If the unit were cooling only, it would obviously not be a "Forced-Air Warm-Air Furnace" and thus there is no restrictions on return air from a kitchen.

If 2009: Table 403.3, category "Food and Beverage Service" - Kitchens (Cooking) has footnote b which states "Mechanical exhaust required and the recirculation of air from such spaces is prohibited (see Section 403.2.1, Item 3). 403.2.1, item 3 states: "3. Where mechanical exhaust is required by Note b in Table 403.3, recirculation of air from such spaces shall be prohibited. All air supplied to such spaces shall be exhausted, including any air in excess of that required by Table 403.3. " So in this case, code is explicit in stating that you can't recirculate from the kitchen. Someone may point out that the RA restriction of 918.6 has added an exception: "Exception: Where return air intakes are located not less than 10 feet (3048 mm) from cooking appliances, and serve the kitchen area only, taking return air from a kitchen shall not be prohibited." However, footnote b pretty much negates this. While 918.6 says you COULD take return air from the kitchen if it is more than 10 feet from a cooking appliance, 403.3 says you can't recirculate it.

 

[Dr. J]

OK, so that is what the code says.

From an engineering standpoint, in many kitchens, the cooling load is greater than what can be served by a make-up air unit sized for the hood, and there is a need to condition the space when the hood is off. A perfectly valid (but illegal) system would have a dedicated unit for the kitchen to take care of the cooling load in excess of the MAU capacity and to provide conditioning without wasting energy on 100% outside air when the hood is off.

 

[RJJ]

Good points Dr.J!