Air Quality Control in a large space

[itsmoked]

I have a bakery that has enough air flow to put a man on the moon. It's ridiculous! You can feel wind on your face and everyone has to talk VERY LOUDLY simply because the company that put in the air extractors and air injectors probably saw the opportunity to make a few more bucks putting in more than needed.

All the units that bring air in from outside thru filters and blow it into the building are VFD equipped. I'd like to add some connection/communication to the VFD and use them to moderate the hurricane.

Often there are only 4 or five people in the 65ksqft building and no baking and at other times there are 40 people and baking and sometimes 50 people and no baking with a big roll up door open.

My question is how would one typically close the loop on this? I need the systems to provide enough air but no more.

What's typically monitored to do this?
CO[sub]2[/sub]?
O[sub]2[/sub]?
PM2.5?
Humidity?
Actual mass flow?

Something else?


Keith Cress
kcress -

http://www.flaminsystems.com

 

[BronYrAur]

It is probably combustion air in addition to ventilation air. It may also include some attempt to remove the over heat rejection by sweeping air across it and out of the building.

With such a low occupancy, I'm sure O2 and CO2 will never change enough. These ovens are vented to the outdoors, correct? If not, that would probably explain it.

 

[itsmoked]

Hi BronYrAur. The thirteen walk-in ovens are all power draft induced to outside.

Then they have a dozen of the large grease trap type extractors that pull air out of the hoods over the ovens. (no grease smoke involved)

It seems to me that the extractors and powered flues alone are probably more than enough which is why we're trying to get a handle on the injectors.

NOTE: One of the powered flues stacks.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[GT-EGR]

Without knowing how many makeup air units you have vs exhaust fans vs hoods, you could use a combination of temperature switches in the hoods or current sensing relays in the baking equipment to tell you when an oven needs exhausting, and have that control your when exhaust fan enable/speed, and then have your makeup air units track your exhaust quantity somehow

On top of that you either need an MAU just for space general cooling/ventilation or have your hood exhaust fans have low speed settings so when not in operation they still keep the room conditioned and air circulating but at a much lower quantity.

 

[itsmoked]

GT; Sounds like sort of open-loop dead reckoning. Ugh.

I was going to use current switches on the oven draft inducers which are unrelated to the hood exhaust fans (EF). When the last draft inducer shuts off after oven turn-off I'd shut down the exhaust fan. The flue draft inducers run for 20 minutes after an oven is shut down.

At the moment I'm considering putting in a suite of sensors indoors and outdoors and watch how they change during daily operations over several weeks.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[chicopee]

Can you get the original copy of the calculations to determine the reason for such presumably high flow rate of air?

 

[BronYrAur]

It looks like there is no heating/cooling in the makeup air units (injectors), so they are just for ventilation. based on what you have said, the exhaust fans (extractors)are just removing heat from above the ovens. The powered flue stacks are removing the products of combustion.

The injector units need to provide enough air to makeup for what is being removed. So, it would seem to me that the exhaust fans should only run when the oven is in operation, or perhaps a little longer to remove residual heat. The powered stacks obviously only run when the oven is in operation. So the makeup air units should probably also only run when the oven is is operation.

Is it a 1-1-1 relationship? 1 makeup unit, 1 powered flue, and 1 exhaust fan per oven? If so, control all 3 units together only when the oven is operating. You said that the makeup air units have VFDs, but what about the exhaust fans? If they do as well, you should modulate them down and see if heat can be adequately removed at lower frequencies. Perhaps they are just oversized. If you don't have VFDs on the exhaust fans, you may go negative as you modulate the makeup air. You want to avoid that.

 

[itsmoked]

chicopee; I doubt it, especially if it was deliberately....stretched to sell more hardware.


BronYrAur; True, No heating or cooling or even any reheat. The powered flues remove the combustion products, yes.
The EFs remove air from the oven hoods but that misses a lot. Commissioning the ovens I filled the top 10 feet of the 40 foot high space with socked-in oven smoke that somehow doesn't make it into the hoods. This was because they hadn't turned on an EF that just pulls from the ceiling just like the MAUs inject. So I believe two of the EFs pull from the ceiling.

The injector units need to provide enough air to makeup for what is being removed. So, it would seem to me that the exhaust fans should only run when the oven is in operation, or perhaps a little longer to remove residual heat. The powered stacks obviously only run when the oven is in operation. So the makeup air units should probably also only run when the oven is is operation.

That makes sense.

In no way is it a 1-1-1 situation unfortunately. The EFs don't have VFDs.

avoid going negative

Check!
One differential pressure sensor added to the sensor suite. I'd need that to deal with having massive roll-up doors opened verses closed anyway.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[nuuvox000]

As far as meeting ventilatoin requirements from the IMC, do they have certain times or certain days that they have the 4 people vs the 40 people? You can have a weekly or hourly timer adjust the outside airflow rate for occupancy based on this. As far as doors being open and closed, if you're trying to maintain a certain positive pressure then you can install a space pressure sensor and hook it up to the makeup air units.

 

[RossABQ]

Is flour dust a consideration? I worked as an intern in a very large commercial bakery and it had high air flows to dissipate and collect flour dust in the mixing areas. They were mixing bread dough in dumpster-sized bins.

 

[itsmoked]

nuuvox000; Sorry about the delay I just saw your response.

do they have certain times or certain days that they have the 4 people vs the 40 people?

Yes! And, they're quite regular.

install a space pressure sensor

Have you got any suggestions; brands, types of these?


RossABQ;

Is flour dust a consideration?

It doesn't seem to be. They use some 5 foot wide torus shaped mixers, like giant Mixmasters at 45 degrees. They dump all the ingredients in followed by the water which all sits for a while then they start slowly and speed up a few minutes in. I only see some flour residue in the motor areas where it slowly builds up before an annual cleaning occurs.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[nuuvox000]

As far as a space pressure sensor, it's pretty simple so it doesn't really matter as far as brands. I would call up a controls contractor and ask them to quote you the sensor, installation, and startup. They will just calibrate it according to the space pressure you're trying to achieve and it will output 0-10 volts DC, typically, and the rooftop unit will ramp up and down based on the voltage that is incoming. Sometimes you'll need a VFD added to the equipment if it doesn't have one already.

 

[itsmoked]

Kay. Thanks.

Keith Cress
kcress -

http://www.flaminsystems.com