Heated Make Up Air Fan required for Hood Exhaust?

[RareBugTX]

Hi all:

I was wondering if someone can provide some thoughts on this topic.
We are designing a roof opening for a new hood roof exhaust fan (2000 cfm, medium to light duty) The question lies in the fact that Code requires us to make up air that is been exhausted, but for a very small sushi kitchen is it justified to provide with heated make up air?.

Are there any options to synchronize the existing RTU to supply more heated air when the hood exhaust fan is on? We are in the midwest and it gets cold in the winter.

I appreciate beforehand your input.

Rarebug

 

[KiwiMace]

Generally speaking, yes. Imagine putting 2000cfm of 20degF air into your small kitchen. You might have a hood ducted makeup or whatever, but it's still a lot of cold or hot/humid air to be putting in a space.

Have a look online at the variable speed melink intellihood controller - although might not payback for your installation.

 

[cry22]

Some jurisdictions allow make-up without heat.
If you put the hood against the wall, captive-aire designs a hood with a supply fan with no heat for the make-up air. count on 20% negative pressure for it to work. that 20% will come from adjacent system, meaning upsizing the adjacent system. I think this is in line with what you want to hear.
Understand that you need to check with your local code official because for most jurisdictions, the IMC requires make-up air to be within 10F of room air temperature.
If your hood does not handle grease, try looking into a heat recovery ventilator.

Now, besides roof openings and Sushi, what's a structural engineer got to do with make-air for a hood?

 

[lemonmugua]

you have to bring 1600 cfm (80% of exhuast air) make up air indoor. Therefore, u need a make up air unit and up blast exhaust fan which are all on the roof. you need an A/C unit. in total, you need 3 openings for the roof.

if your unit is over 5 tons, you need an economizer for energy efficiency.

 

[paultg]

This is a good resource for kitchen exhaust/make-up design considerations by Reznor:

https://www.rezspec.com/cms_download.php?mod_files[fileid]=000000000589

Greenheck has one as well:

http://gfcportal.com/products/kitchen/application_guide.php

To answer your questions:
1. I suggest you temper the make-up air.
2. Depending on the existing RTU coil selection (or heating/cooling capacity) and fan selections, outside air intake size, etc. you could try to interlock its operation with the kitchen fan. When the exhaust fan runs the RTU OA damper would need to open, and if applicable the supply fan would need to increase in speed to deliver more air (at a higher OA percentage) to the occupant space and kitchen area. If it has a return fan some some control for it is also needed. This is done alot when large dinning areas are directly adjacent to the kitchen (or open to it) such as in a cafeteria. Keep in mind air velocities across the coils and fresh air intake, as well as ductwork sizes and fan capabilities would need to be reviewed in detail.

It really depends on the layout of the spaces and how they relate to each other. It might be cheaper to just buy a dedicated MUA unit with heating (and maybe some cooling) for the kitchen. Keep in mind if you decide not to cool the MUA you are adding a space load to the kitchen (raw outdoor air that is not dehumidified).

Paul G.

 

[RareBugTX]

Hi all:

I really appreciate your feedback and your responses have helped me a lot to understand some of the basics of these systems.

Cry 22: Answering to your question, well, this sort of problems have kept coming to my office for six years now, where architects have just delegated them to me when they are not able to provide with solutions that make sense and I have taken on the task of resolving them, and to be honest, I like it. Initially I was asked only for the structural part, but that is way too easy to resolve because these types of systems do not typically pose a structural feat hard to resolve within 5 minutes. So I decided to figure out some of these straightforward systems and I am willing to continue to do research and understand them.

Kiwimace, lemonmugua and Paul TG thanks for the links

Best regards,

Rarebug

 

[mauricestoker]

Fishnick.com gives very good guidance. The integration of the MUAU with building system is pretty good.

A good first step might be looking at what climate zone you are in, then chapter 6 of the ASHRAE 90.1 manual.

The owner might be elgible for energy rebate for demand control ventilation.