Question about Air Balance

Hey guys, long time browser, first time poster. This site is absolutely great.

This will be the first summer with a new make up air unit and when it was balanced it was quite cold out. Now that its getting warmer, the make up air is blowing warm air into our kitchen and the a/c cant keep up. I’ve also noticed when it started getting warmer, the doors are being sucked shut and making it more difficult than usual to open. It also sucks in massive amounts of air when its cracked open.

Any ideas?

Thanks guys!

i Pizza head:

You are the perfect example of why we do not use make up air units when we equip pizza shops.

Make up air units warm winter air but do not cool the summer air. You are going to roast in the summer. Your A/C will struggle but will not be able to keep up.

You indicate your building has a low interior air pressure causing you doors to be difficult to open and outside air rushes in when you do get them open.

Its apparent your hood is takeing more air out of your building that your A/C and make up air can supply.

Simply stated your ventilation system is not properly designed. You will have problems until you make some dramatic changes in your system.

If you will answer a few questions I will try to help you.

What is the size of your building? Any many.
What is the size of your hood? How many CFM is being exhausted?
What is the size of your make up air unit How many CFM is being brought in?
What is the size of your A/C. Does your A/C bring in fresh air or does it just circulate inside air through the unit?

You may want to look a bit further down on this forum I have some ventilation information there. Not enough to solve you problem but you may find it interesting

Is this a heated makeup air unit? i get the impression that the unit is not running at all when its warm outside, therefore, the arrival of the negative pressure in the building when its warm.

Ive seen instances where the A/C units will put a positive pressure on the building through the use of an economizer, but it wouldnt put a negative pressure on the building.

Thanks for the post guys! This site never ceases to amaze me.

But to answer some questions!

The village we are in had made us install the make up air unit b/c of the kitchen equipment.
1150 sq feet; 850 kitchen, 300 carry out (no seating)
Not sure the cfm, but the hood is 8 feet with ansul system and make up air.
I have 2 3-ton a/c units. One for the front and one for the kitchen. I believe its fresh air and they both are economizers.\

Thanks again guys!

Ouch! I had a 7.5 ton unit that mostly (98%) served the kitchen of approximately 450 square feet, and it couldn’t keep up. granted we didnt have a makeup air fan, just whatever cfm was sucked out by the exhaust was also sucked in through an 18" vent in the center of the hood (no fan), but still…

Hi Pizza head:

Your hood could be removing up to 3200 cubic feet of air per minute. Your make up air unit is probably designed to bring in an equal amount of outside air and it no doubt heats that air during the colder months. Most make up air units do not cool incoming hot air during the warmer months and when running your unit can be bringing a lot of hot air off your roof.

As you apparently had no pressure problems during the colder season it appears that your make up air unit may not be running at all or is not running fast enough to bring in enough air to compensate for the air being exhausted.

As to your A/C you need to add a substantial amount. About the first Five ton of A/C in a pizza shop just balances against the heat of the equipment and does not cool the area, With 5 ton for the equipment and probably another 4 or five ton to cool the building then enough A/C to off set the in coming make up air, you will need a lot more A/C. If you can find out the CFM of you make up air unit I think you will need a ton of ac to cool each 400 CFM of make up air.

We never use a make up air unit in a carry out pizza shop. We use patented certified hoods that require only about 1/2 the air to be exhausted. We them bring most of the required make up air directly into the hood itself. We drop that air down a hollow panel extending across the rear of the hood and then deflect that air up and around the ovens and out the hood. That air stays in and is exhausted from the hood with out entering the room. With that system we need take only about 800 CFM of air from the building. That air is supplied by as little as 5 ton of the A/C which you are going to have any way so there is little or no additional cost to cool it.

With the above system there is no cost of operating a make up air unit (that cost is about $1.50 per year per CFM or about $4500.00 per year for a 3000 CFM MUA unit). also there is no cost of cooling the summer make up air.

The system we use costs about the same as a non certified hood and make up air system.

Ventilation in a dine in with more than a few seats and additional cooking equipment is a different ball game but a properly designed system using certified hoods can usually save a lot on operating costs there also.

George Mills

Thanks George, always great to hear your expertise.

But in English… I have a bad setup and to fix it would cost lots of $$?

I think one of the main reasons we didn’t go with a bigger a/c is because our building is only a 1 phase. I believe they said that anything over 3 ton has to be 3 phase, but I could be wrong about that.

I should also mention that it is isn’t that hot in the kitchen. Even on really hot days, it doesn’t get any warmer than 89. Most days its about 78 in here.

Thanks again guys!

I think one of the main reasons we didn’t go with a bigger a/c is because our building is only a 1 phase. I believe they said that anything over 3 ton has to be 3 phase, but I could be wrong about that.

I should also mention that it is isn’t that hot in the kitchen. Even on really hot days, it doesn’t get any warmer than 89. Most days its about 78 in here.quote]

Hi Pizza head:
You mentioned your pressure problem and I indicated that your make up air unut probably was bringing in to little or no air causing that problem.

Your statement that it is not getting extremely hot in the kitchen is possibly because the make up air is not working, therefore it is not dumping hot air into your kitchen.

You may be in a catch 22. You will have to get your make up air unit delivering the proper amount of air and that will probably result in raising the inside temperature of your building.

George Mills

I’m wondering, are you stating this to solve the door pressure problem? B/c I think I’d rather have the door pressure problem over a hot kitchen any day.

Thanks again George.

Hi Pizza head:

You should not have to put up with those 2 problems.

Because of your negative building pressure you are not only pulling in outside air when the doors are opened but some air is filtering in from every crack and crevice and your A/C is being wasted trying to counter that heat.

When the weather turns cold you will have chilling drafts constantly and very cold breezes when doors are opened.

Because you are connected to a make up air unit that does not cool the incoming outside air you will always be warmer than you should be in the summer.

The only solutions are to redesign and install a proper ventilation system or add a lot of A/C.You can bite the bullet now and buy a proper ventilation system or continue to pay the high operating cost of make up air and waisted A?C

How much A/C do you have now?

George Mills

pizzahed, you can definitely have single phase A/C units larger than three tons. I only have single phase at my house but a four ton unit. I’m pretty certain that both 5 ton units I have at work are single phase.

Comment on the above: In almost all pizza shops the first five tons of A/C does nothing to cool the workers. It takes at least 5 tons of A/C to break even with the heat
created by the equipment.

George Mills