When it comes to progress, refrigeration and freezing systems have a certain inertia. They’re big and expensive, and they run according to long-established principles of mechanics, chemistry and physics. All of that works against sweeping innovation.
But improvements are gradually taking hold – snowballing, if you will. Some of these are unique to chilling; others are general trends in all kinds of processing equipment.
Among the latter is increasing interest by end users in sanitary design. For a long time, efficiency, in both capital costs and operation, was the top priority. But now, material choice and design increasingly are being dictated by food safety considerations, especially sanitation.
“I’d say definitely the food safety side has taken precedence over anything else in the past two years,” says Mike Anderson, sales manager for Air Management Technology (www.airmanagement.com), a design-build firm for thermal process supporting solutions.
Sanitation is linked to both food safety and efficiency, says Torbjörn Persson, director of sales for spiral freezers at JBT Corp. (www.jbtc.com/foodtech), whose brands include Frigoscandia and Northfield.
“Food safety becomes visible through higher demands on hygienic design and on more efficient and safe cleaning systems,” Persson says. “When it comes to efficiency, we see that increased demand on longer continuous operating times and in shorter turnaround times, which usually is about making the cleaning cycle as efficient as possible.”
The drive for sanitation is partly a matter of designing equipment for easy cleaning, according to principles that have been established for all kinds of food plant machinery: no sharp corners or creases, no protrusions like bolt heads – basically, no places where dirt, product residue or other contamination could accumulate.
Another aspect is a little more problematic: choice of materials. For blast freezers, especially large boxes like spiral freezers, galvanized steel and aluminum was the most common material for the refrigeration equipment, along with insulated metal panel wall construction, because it delivered the required performance for relatively low cost. But Anderson says with strict food safety requirements, users are increasing requests for all-stainless components, which can better withstand harsher sanitation chemicals.
“The challenge is trying to fit the return on investment with all these enhancements, because [customer] still want to pay the same amount as they did when it was made of galvanized materials,” Anderson says. “Food processors understand the greatly extended equipment lifespan and food safety enhancements stainless offers. The challenge is to minimize additional capital investment.”
The extra expense comes in two ways: most all-stainless refrigeration equipment is custom-made compared to “off the shelf” galvanized components, and stainless steel is just more expensive than galvanized.
One of the biggest challenges in freezer sanitation is getting the inside completely dry before bringing the temperature back down. Because freezers are almost totally enclosed boxes, drying them out is difficult, even with powerful fans.
“Drying has typically been done by running fans at high speed, much like a dishwasher,” Persson says. “But then, the problem is – much like a dishwasher – if you don’t open the door, it never really gets dry because it’s hard to get rid of all the moisture. And what happens is you end up with a very warm freezer that takes a long time to chill down, and you still have a lot of moisture in there.”
To alleviate this, JBT has developed the LVS QuickDry. It attacks the central part of the problem: moisture freezing on the evaporator coils, the coldest component in the freezer.
“The LVS QuickDry condensates the moisture to the evaporator before heating it again quickly using hot gas, so the moisture that has frozen to the evaporator drips down to the floor,” Persson says. “This gets most of the moisture out of the freezer as quickly as possible.”
Another potential safety issue has to do with choice of refrigerant. For a long time, ammonia was king, and it still is. Ammonia is cheap, reliable and doesn’t harm the ozone layer or otherwise contribute to global warming – unlike a major alternative, R22, which is being phased out. After Jan. 1, 2020, it will be illegal to produce or import R22 in the U.S.
The problem with ammonia is that, while it doesn’t cause global warming, it can be dangerous. It's highly toxic, so leaks in a refrigeration system potentially can be lethal. This is why it’s allowed only in industrial systems, which, at least in theory, have the necessary monitors and alarms. Nine incidents of industrial workers coming into contact with ammonia were reported to the Occupational Health and Safety Administration in 2017, with results ranging from no injuries to second-degree burns.
One way to lower the chance of ammonia exposure is to limit it by using ammonia in conjunction with a more benign refrigerant, like carbon dioxide. This is done in what’s called a cascade system, which is basically a two-part refrigeration setup. The ammonia cools the carbon dioxide during the condensation phase of its refrigeration cycle; the CO2 then enters the evaporator coils, which it chills to generate cold air from adjacent fans. This setup confines the ammonia to the inner works of the refrigeration system, away from people and products. It also can handle lower temperatures than an ammonia-only system.