Air Flow Design: The Common Oversight in Food Plants | Part 1/4

Posted by Admin on Mar 16, 2017 7:08:53 PM

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In the process of developing a design for a food production facility, there are so many things for an owner/operator to consider: capital financing, access to raw materials, proximity to distribution points, layout of process equipment, future expansion capabilities, adequate staffing and employee welfare facilities among many others. It’s no wonder airflow, the movement and filtration of an invisible gas, within the facility can get overlooked. However, properly designed and installed airflow systems are essential to a clean and safe food production environment.

 

While 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
  • Filtration
  • Pressurization
  • Temperature/Humidity

In this blog series we will explore each of these four common considerations. Let's begin with air distribution.

 

Air Distribution

 

Good airflow design in any facility begins with proper distribution of the air. In order for the system to achieve the performance required for a safe food production environment, air distribution needs to be even throughout the production spaces to provide a platform for achieving proper filtration, pressurization, temperature and humidity conditions. The distribution ductwork will need to be accessed for cleaning and swab tests and also be located away from open product.

 

There are many cost effective solutions to achieving good air distribution, particularly when designing a new facility. A variety of air terminal devices (grilles, registers and diffusers) are available depending on the application. Fabric duct (sometimes referred to as duct socks) are a type of duct and terminal device in one that offers some real advantages in both first cost and performance.

 

Most manufacturers of air terminals publish air velocity and distribution charts for designers to use to assure even air distribution. Velocities down to 50 or 25 feet per minute are typically adequate for particulate, temperature and moisture control. Designers should perform analysis of the terminal devices to assure they can achieve some level of air movement in all areas of the production room. This can be done simply by drawing arcs around a dimensionally accurate plan showing the location of the terminal devices. The arcs represent the distance or ‘throw’ of each device. More sophisticated analysis may include the use of computational fluid dynamics (CFD) models. Air flow and velocity analysis can also be performed by most manufacturers of fabric duct systems aiding in the final layout and sizing.

 

Another equally important aspect of even air distribution occurs on the return air side. If all the air returns in one location, air is more likely to short circuit and not distribute to all areas of the room causing uneven temperatures, localized humidity issues and buildup of particulates. It is preferred to spread out the return air inlets and locate them in opposite elevations as supply air outlets (typically lower to the floor since most supply air is distributed up high). 

 

When this cannot be accomplished, selection of air devices should be done more carefully and include additional analysis on overall distribution of air. This can be done by reviewing vertical sections of the building to see if the air devices are able to deliver air to the lower part of the spaces. It may be appropriate to evaluate whether a CFD model is necessary to assure that airflow is being evenly distributed. Once considered for more specialized applications, the lower cost and greater usability of CFD software is making it more practical for use in evaluating heating, ventilating and air-conditioning (HVAC) systems.

 

Part 2 explores filtration and the removal of contaminants from the air stream

 

Would you like to discuss all of the airflow design considerations now? Contact our expert, Frank Mangin at frank.mangin@haskell.com

 

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Topics: Food Safety, Manufacturing