Food safety and temperature go hand in hand. It takes only a few degrees difference in temperature to cause spoilage—whether it be from bacterial growth due to warm conditions or frost damage due to cold. Temperature also affects humidity, which can wreak havoc on both packaging and on food itself.
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Explore This IssueJune/July 2017
Maintaining proper food storage temperature and humidity can be challenging enough in a home, restaurant, or retail setting. However, in large manufacturing and warehousing facilities, the challenges are compounded by storage and access issues as well as the sheer volume of space involved.
Air Stratification and Distribution
One of the biggest issues in warehouse temperature control is caused simply by the nature of the buildings involved. Many of these facilities are thousands of square feet large with 20- to 30-foot high ceilings. Wherever you have a large, high-ceiling space, air tends to stratify. Warmer air rises and cooler air settles, resulting in horizontal layers of air with differing temperatures. This can pose a number of problems, including:
- Difficulty maintaining consistent storage temperatures;
- The formation of cold downdrafts and/or chimney effect, which can adversely affect workers; and
- Unhealthy air conditions due to stagnant, stratified air—which harbors bacteria, molds, and viruses, as well as fumes from forklifts and other equipment.
HVAC alone is not enough to relieve these problems. What is needed is an effective air distribution system. By circulating air from top to bottom throughout the space, the temperature differential can be reduced to a minimum—along with the problems it causes.
One of the most cost-effective ways to address this issue is through the use of fans. Large, industrial sized high-volume low-speed (HVLS) ceiling fans in particular are especially effective at mixing air in large spaces in an energy-efficient manner, without causing uncomfortable drafts or spots that are too hot or cold.
Shutting the Door on Temperature Loss
Another problem faced by most food storage facilities is temperature loss during access to the structure. Warehouse doors and loading docks are typically quite large and allow correspondingly large amounts of air in and out when they are opened. This can lead to frustration when trying to maintain a stable temperature within the building while transporting goods and materials in and out of the structure.
The challenge is to design doorways to enable easy access for both people and goods while minimizing air exchange. Door design plays a critical role in this endeavor. Ideal door design depends on many factors, including location in the building, the equipment to be used, desired temperatures and temperature differentials, and how often the door will be used throughout the day. Effective designs range from heavily insulated cooler doors to high-speed doors, or even vinyl curtains.
Another strategy that can be very effective, especially where a high degree of access and mobility is desired, is to divide two air spaces with air itself through the use of an air curtain. This consists of one or more blower fans positioned above the opening between two spaces, which directs a stream of air downward. The air current effectively separates the two spaces without impeding entry and exit. This works best when there is little pressure differential between the two spaces.
While specialized air curtains or air doors are commercially available for doorways, it is also possible to create an air curtain effect across a larger space by installing a line of small HVLS fans across the ceiling.
Temperature and humidity are closely related, and any attempts to control temperature in a warehouse situation are sure to affect humidity levels as well. While improper humidity levels can adversely affect any product, maintaining proper humidity levels is especially critical were food storage and handling take place. High humidity can encourage mold growth and degrade the quality of many food items. It can also compromise food packaging. Conversely, some food products, like fresh produce, require high-humidity levels to maintain optimal freshness.
Where two adjacent spaces must be kept at different humidity levels, the most common solution is to use an insulated barrier wall or fabric curtain wall, along with mechanical humidity control devices such as chillers, humidifiers, and/or dehumidifying units.
On the other hand, in a large space, it’s quite common for humidity levels simply to rise too high. Overly humid air is an especially common problem in food packaging facilities where hot water is used in cooling and sterilization procedures. In this case, it might be necessary to install a large-scale industrial dehumidifying unit or system.
There are numerous types of industrial scale dehumidifiers available on the market. Some use chemical desiccants to remove moisture from the air. Others, such as direct-expansion systems and heat pipes, work in conjunction with the air conditioning system. Each system has its pros and cons in terms of cost, energy efficiency, and capacity.
Another approach that can be used on its own or in conjunction with an air-conditioning system is evaporation. This approach uses fans to create air movement that moves humid air away from the area. It also creates an evaporative cooling effect that can reduce worker stress. This is especially true of HVLS fans, which operate without creating undue drafts.
Condensation is, of course, a humidity issue. However, it is also a temperature issue. Condensation happens when warmer air flows over a cooler surface. If the surface is cool enough, the air will hit the dew point and coalesce into droplets, which then collect on the surface. It’s possible to have condensation even without overly high humidity, where temperature differentials are great enough. That said, high humidity exacerbates the problem.
Condensation is a common problem in warehouses, especially at humid times of year. It can contribute to all sorts of safety issues, such as sweating slab syndrome and slippery handrails, as well as compromising product quality. Because of the huge temperature differentials involved when coolers and freezers come into contact with warmer air, condensation is also a very common and serious issue when it comes to food storage.
There are two ways to fight condensation: reduce humidity or decrease temperature differential. The latter isn’t always possible in a food handling situation, since coolers and freezers by their very nature require a temperature differential. However, in certain cases, it is an effective approach. For instance, correcting air stratification problems in a large warehouse space can relieve condensation issues by creating a more uniform interior air mass as well as through the evaporative effect of moving air.
One of the biggest temperature control challenges for large food handling facilities and food storage warehouses is maintaining safe temperatures cost effectively. Implementing energy-efficiency measures can significantly reduce costly energy loss, but care must be taken to allocate resources on high ROI improvements. Considerations include the following.
Energy-efficient lighting. LED bulbs are the most efficient available, and their long life reduces maintenance costs significantly. They emit very little heat and therefore reduce cooling costs, and are cold-tolerant for efficient lighting for freezers and coolers. However, high-efficiency fluorescents usually cost less upfront and may be more cost effective, so it’s a good idea to run the numbers before investing in lighting.
Shell measures. Limiting energy loss through the building’s walls with measures such as insulation, weatherization, energy-efficient doors and docks, and cool roofs will significantly reduce HVAC costs. It will also allow cooling equipment to run less, which saves electricity and extends equipment life.
Pipe insulation. Older cold storage facilities should be examined for uninsulated or poorly insulated piping. Insulating just 400 feet of pipe can save a facility $27,000 per year, according to the Global Cold Chain Alliance.
Automation. Smart building technology automatically adjusts controls for maximum energy efficiency and allows warehouse HVAC and food storage units to be controlled remotely, saving on labor costs as well. When purchasing fans and other equipment, look for units that can be tied into an automated control system.
Finally, it’s important to remember that high-tech solutions aren’t always the most cost effective. Sometimes a solution as simple as installing a ceiling fan can alleviate temperature and humidity problems just as well or better than fancy HVAC equipment.
Carlson is the CEO and owner of Go Fan Yourself. Reach him at firstname.lastname@example.org.