We love balance in our lives. Work-life balance, a balanced diet, a balanced budget, even a balanced building. Wait a minute? A balanced building? What impact does a balanced building have on our lives? A building that is not balanced contributes to uncomfortable spaces, elevated energy costs, odor issues, insect infestations and finally moldy buildings. While you can’t see it, you can see the symptoms of it – especially in kitchens. Since the kitchen is a relatively small space that has lots of air coming in and going out, it’s high risk, enemy-number-one, for a poor air balance.
Let’s simplify a commercial kitchen to a smaller scale, without all the stainless steel and heat. Imagine if you take a cardboard box (inside the box is the miniature kitchen) and close it up, as if you were shipping something in it. Cut a hole, just large enough to put the nozzle from your vacuum into, and turn on the vacuum. Aside from the noise, you’ll find the box sides are pulled inward and the vacuum is pulling air from the interior. Where did that air come from? It leaked in around the flaps in the box and the opening for the nozzle. This is analogous to having a kitchen with hood and exhaust fan running, no make-up air, no windows open and no doors open.
Now, what if we put another hole on the other side of the box and connect the other side of the vacuum (that blows air) to that opening, so that both are hooked up to the box? Well, with the air sucked out one side and blown in the other, the box is just windy inside, but the sides of the box won’t be sucked in or bow out. The inside of the box is no longer under a “vacuum” and is about the same pressure inside with the space around it. It is “balanced” because the same amount of air is coming in and leaving.
As a last step, what if we disconnect the originally installed vacuum suction hose? Cover that hole we made for it with tape. Now the box will bow out and be pressurized by the vacuum cleaner blowing air into it. This is like a building with air coming in and none leaving (make up air running and no exhaust).
In the commercial kitchen, we have air removed from the space (exhaust) through the hood and out of the building (this is what the suction hose on our vacuum represented). We bring air back inside through make-up air units (this is what we represented by the discharge hose of our vacuum). If the building has equal amounts of air coming into it as it does leaving it, we are balanced. However, it’s never that simple when there are multiple fans bringing air in and taking air out of the space (bathroom fans, air conditioning units/heaters, etc.) …
It hangs in the balance
In the original building design, a kitchen is supposed to have slightly less air being supplied to it compared to the other spaces. This keeps any air movement into the kitchen from other spaces and keeps odors contained in the food preparation area. If, however, there is a significant difference in the air being removed from the kitchen compared to the air coming back in, we can start to have significant issues. In an extreme case, we can create a back draft condition for gas appliances, like vented water heaters, where the gas is pulled out of the appliance and into the room (not through the burner or flue it is supposed to travel), which could be explosive.
In less extreme cases, the pressure differential pulls air in from the doors and windows and cracks in the building façade, anywhere it can get the replacement air. Air is a fluid and seeks the path of least resistance. Too much of that in the summer with humid outdoor air and cool air-conditioned surfaces creates moisture issues and can lead to mold. Every time a door is hard to open and sucks air in from outside, insects are pulled into the building with that outside air to the food prep areas. Of course, hot and uncomfortable or cool and clammy kitchens make for less productive workers, too.
The alternate condition
Having more air introduced into the kitchen than what is exhausted can create issues, too. There may not be enough exhaust air to remove the cooking heat and effluent. It’s akin to overfilling a bathtub, the drain can’t keep up with the amount of “water” being added back in, so it overflows. The smells in the kitchen migrate to other lower-pressure areas of the building. The hood may not capture and contain smoke as well in a positively pressurized environment.
To add to the mayhem, if there is ever a problem with the hood capturing the smoke, the first reaction is usually to increase the exhaust (remove more air). While this seems reasonable, this doesn’t help if the smoke isn’t making it into the hood to begin with. Have you ever sucked out your birthday candles? You can’t, although blowing them out isn’t too hard (if you don’t have that many!). When we increase the exhaust in a space that is already un-balanced with too much exhaust leaving, we exacerbate the problems from the un-balance.
All of this airflow balancing is carefully engineered when the building is originally built, and all the new equipment installed, this is all checked and verified. Even so, measurements in the field are acceptably accurate but not precise and it’s possible that air is being introduced or exhausted in ways we didn’t expect or measure. Further, after the building has been in operation for a year or more, the characteristics of these mechanical systems may have changed (stretched fan belts, clogged filters, etc.). Therefore, it’s important to periodically re-commission the building and have a test and balance performed. It’s also important to realize that neglecting the airflow differences that you can’t see can create expensive problems that are quite visible. It all hangs in the balance.
Regional Sales Manager, Halton
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