Air balancing in food preparation plants
Air balancing in food preparation plants
(OP)
I work for a refrigeration company. We design and install industrial refrigeration systems for packing houses, refrigerated warehouses, and processing plants.
It has become a increasing concern in these plants that air-borne particles drift from ”clean” areas of the plant to the “dirty” areas – ( cooked area of food preparation plants to raw, or cut areas toward kill areas of slaughterhouses ). E-Coli and other health emergencies have made air drift in plants a public safety issue that is taken very seriously by our customers.
Our company installs air handling equipment for refrigeration, so we have become involved by default. I am with the electrical department, my primary job functions involve PLC control and instrumentation equipment. We are having difficulties getting accurate measurements of static room pressures. Our problems, I believe are due to the miniscule pressure differentials we are trying to achieve and air movement in the areas we are trying to control. It is hard to get a sample in a room where there is no breeze.
Air is constantly moving and doors opening and closing. We have the same problem with outside air.
Another problem we have encountered seems to be differential transmitter response drift due to ambient temperature of the transmitter.
I am looking for stable instruments and technical advice in these areas.
We have been using air make-up units and exhaust fans – both with and without damper and VFD controls. Our problems are not control of the equipment, but reliable indication of the room pressures.
It has become a increasing concern in these plants that air-borne particles drift from ”clean” areas of the plant to the “dirty” areas – ( cooked area of food preparation plants to raw, or cut areas toward kill areas of slaughterhouses ). E-Coli and other health emergencies have made air drift in plants a public safety issue that is taken very seriously by our customers.
Our company installs air handling equipment for refrigeration, so we have become involved by default. I am with the electrical department, my primary job functions involve PLC control and instrumentation equipment. We are having difficulties getting accurate measurements of static room pressures. Our problems, I believe are due to the miniscule pressure differentials we are trying to achieve and air movement in the areas we are trying to control. It is hard to get a sample in a room where there is no breeze.
Air is constantly moving and doors opening and closing. We have the same problem with outside air.
Another problem we have encountered seems to be differential transmitter response drift due to ambient temperature of the transmitter.
I am looking for stable instruments and technical advice in these areas.
We have been using air make-up units and exhaust fans – both with and without damper and VFD controls. Our problems are not control of the equipment, but reliable indication of the room pressures.





RE: Air balancing in food preparation plants
The operating range is 0°C to 50°C.
You will get space fluctuations if you are not able to maintain the necessary airflow offsets to maintain the appropriate pressure differentials. If you are expecting the doors to open and close frequently you may consider putting a vestibule in (ante room essentially) to mitigate sudden changes in pressure difference.
RE: Air balancing in food preparation plants
RE: Air balancing in food preparation plants
In order to get stable pressure readings ,the reference point locations should be carefully chosen.
RE: Air balancing in food preparation plants
Sometimes plastic vertical sheet doors are used to separate one area from another. It is unusual to get involved in room preesure control to the same extent as in for instance a clean room or theatre.
The same principles are often used, i.e. supply clean air to clean areas and extract dirty air from dirty areas. Encourage airflow in the right direction.
Experienced food factory designers may use the 'protected door' principle whereby you may protect a clean food space from a dirty food space by ensuring that the airflow across the free opening of the dividing doors is maintained at a certain 'control velocity'. (i.e. 0.25m/sec)
This can give high interrelational airflow rates and can be quite difficult to achieve.
For a single door opening you might need for example 0.50 m3/sec airflow through it to maintain a 'clean/dirty' relationship.
Often food factories have huge air handling units with F7 filtration or better.
Do I take it from your question that the regulations in your country require room pressure diffential control with monitoring. If so..good luck...it is very difficult to achieve in large fully operational work spaces.
Any monitoring should have a time delay alarm built in otherwise your panel alarms will be going off all the time
Friar Tuck of Sherwood
RE: Air balancing in food preparation plants
Generally the pressure diferentials of 15Pa are adequate with closed doors. The open door velocity requirement should also be applied to ensure no back flow into the clean area. as stated the basic facility layout is key to controlling airborne contaminants. If you have an existing facility to bring up to speck good luck!
Mark Hutton
hutton4eng@picknowl.com.au
RE: Air balancing in food preparation plants
since you probably have rather large rooms it is very easy to have draft even if you don't open door ferquently - temperature differnces in room, obstacles to air flowing in and out of air distibution equipment are sufficiant to cause this.
The only area where I saw pressure measurement practicable is operation and intensive care rooms in hospitals, but only if you have installed equipment that should assure almost laminar flow of air (pereorated walls/ceilings, radiation panels with minimal convection and similar).
This equipment can have cost justification just in such areas and in pharmaceutical industry.
So I beleive that you need different way to control air transmission from room to room.
One solution is to provide little larger difference between make-up and exhaust air. You can even install directional transmission grilles between such rooms, and add adequate filter to the frame if you are still afraid of non-wanted air flow. You can also make oppostite difference in dirtier room (more exhaust than supply).
That is very similar to ordinary toilet venting design, but it is still the most efficient. Pressure sensor in one position in room will give you just indication of pressure on that location, and is not something you can rely on for critical matters.
...and it is not something which fights e-coli. If such thing apperar, you have several weeks shutdown of the whole plant, no matter how good and reliable systems you generally have.
RE: Air balancing in food preparation plants
RE: Air balancing in food preparation plants
Mark Hutton
hutton4eng@picknowl.com.au