While we understand there are many nuances to airflow design and unique considerations based on the type of facility, layout of the facility and what is being produced in it, some of the common considerations that apply to most facilities include:
- Air Distribution
Pressurization is important in the control of contamination within a food production facility. Many operators want to keep the exposed, cooked foods positively pressurized relative to the raw ingredient or finished goods storage areas but are unable to do it cost-effectively. This can be due to a variety of reasons such as too many openings between spaces, not enough outside air, or inadequate air handling equipment and controls.
The first step to ensuring proper pressurization of a facility is to determine the pressure relationships desired. Some plants have a variety of environments from clean to dirty (e.g., raw product, cooking, packaging and finished/packaged product). These areas will typically have varying levels of cleanliness requirements resulting in varying degrees of filtration and pressurization relative to each other. The cleanest area is typically where the food product is going into its primary packaging. For example, starting with an outside air pressure that is defined as neutral or “0”, the various areas of a processing plant may have the following pressures relative to each other:
The building construction and layout are important to maintaining proper pressurization. The quality of the exterior and interior wall construction between spaces of different environmental conditions determines how easy or hard it will be to maintain pressure. Even though there will be openings in the walls for movement of product and personnel, that doesn’t mean that the rest of the wall can have leaks as well. Every crack and opening results in a transfer of air and unnecessary openings result in more air transfer and potential contamination.
Plant layout can have a significant impact on the ability to maintain proper pressurization. A straight-line plant layout has a lot of advantages for air flow design but is rarely practical from an overall space planning and operations standpoint. The advantage is that it avoids spaces that are of varying pressurization being next to each other (e.g., a +1 next to a +3 and a +2). Given that it is often not practical, air flow designs often have to accommodate multiple pressure zones adjacent to each other (more on that below).
One overlooked key to successful pressurization control is the sensor that monitors the pressure between spaces. Some facilities do not have sensors at all and rely instead on the initial air balancing of the facility to maintain pressure relationships. Unfortunately, those relationships will drift significantly over a short period due to belts varying in tension, filters loading up with particulates, and general wear of the equipment. Rebalancing the air handling equipment to maintain the pressure relationships is impractical. Even if the equipment was rebalanced frequently, the outside air pressure varies as weather changes occur. As a result, many of these facilities are not meeting their pressurization needs.
Because of the differential pressure relationships, air will flow from one space to another. Eventually, the air flowing from room to room will flow out of the facility to the outdoors. Since what goes out, must come in, outdoor air will have to be treated and introduced into the facility. The goal is to maintain the pressure relationships with the least amount of outdoor air as possible to reduce initial and operating costs, as outdoor air can be expensive to provide.
Some facilities install pressure sensors and control fans and dampers to maintain pressure relationships. This can be an effective method, as long as the right sensors are being used. Too often poor sensors subject to high levels of inaccuracy and reliability are installed. This results in the need for excessive outdoor air and maintenance on the sensors to keep them calibrated and can often be the same as when relying on initial air balancing.
The best results come from utilizing a highly accurate and reliable pressure sensor, similar to those used in labs. For example, a high-quality sensor may cost $1,000 more than a typical sensor, but can potentially save $10,000 in the initial cost of the air conditioning system, and $1,000’s per year in energy savings. The correct sensor can reduce the need for outside air to 1/10th of the cheaper sensors. These savings continue throughout the life of the facility saving energy costs every year. More importantly, proper pressurization is more reliably achieved throughout the life of the building without as much need for rebalancing and recalibration.
Did you miss Part 2? Read it now. Stay tuned for Part 4 as we explore temperature and humidity.
Would you like to discuss all of the airflow design considerations now? Contact our expert, Frank Mangin at firstname.lastname@example.org.