The Cool Factor: What to Look For in Efficient Freezing and Chilling Equipment

Industrial refrigeration achieves efficiency without sacrificing performance thanks to advances in automation, safety, and sustainability.

raspberries in cryogenic tunnel freezer
Cryogenic refrigeration can reach substantially colder temperatures and chill products much faster than mechanical refrigeration.
Photo courtesy of Air Products.

Industrial refrigeration has long been an effective way to protect the quality and safety of perishable foods. Freezing and cooling equipment have been vital to helping manufacturers extend product shelf life while preserving flavor and texture. Over the last few years, food manufacturers have been able to further reap the benefits of industrial refrigeration thanks to advances in automation, safety, and sustainability, which have helped to improve the performance and efficiency of today’s freezing and cooling equipment.

“The demand in the marketplace for frozen and chilled foods has dramatically increased and so has the demand for refrigerated distribution systems,” says Andrew Pipkin, director of project development at Stellar, the Jacksonville, Fla.-based design-build firm. “As families trend toward spending more time—valuable time—with family members versus preparing meals, we’ve seen the marketplace trend heavily toward the frozen and chilled food sector and prepared food sector.”

Starting point

As frozen and chilled foods continue to increase in popularity, manufacturers are looking to meet those growing production demands with freezing and cooling equipment that can maximize efficiency and boost capacity and throughput. When selecting industrial refrigeration equipment, manufacturers should primarily consider lifecycle costs, which assess long-term reliability, efficiency, and performance of the equipment to deliver optimum return on investment, according to Pipkin. Processors should not only keep in mind the initial capital outlay, but also analyze the costs of operating the equipment over its lifespan, including energy consumption, maintenance costs, repairs, environmental impact, regulatory compliance, potential equipment downtime, and labor costs.

Pipkin recommends that manufacturers conduct a cooling load calculation. Industrial refrigeration works most efficiently when it operates at a full load, but that rarely occurs. A cooling load calculation evaluates if the freezing or cooling equipment can efficiently remove heat while maintaining temperature setpoint conditions. It prevents manufacturers from missing productivity benchmarks, as well as helps them avoid process inefficiency and wasting energy.

“It’s very important to have a proper load calculation done, taking into account all considerations for not only the peak performance, but the average performance as well as the lower-scale performance,” Pipkin explains. Refrigeration systems are typically designed for that one or two hottest days of the year in order to be able to reject the necessary amount of heat under the most strenuous conditions, he adds. “Every other day it’s running at something less than peak capacity just because it doesn’t have to work as hard to be able to reject the heat on those other days.…And that’s a lot of the challenge in refrigeration. You [must] have that turndown capability in order to not have the short-cycling issues and premature equipment failure. Looking at the big picture and designing for the low load scenario an owner might face is just as important as designing for peak load capacity. Low load conditions can be much more common and, therefore, have a higher impact on energy consumption than peak capacity for some systems.”

Drive for efficiency

To ensure freezing and cooling equipment operates efficiently, many industrial refrigeration experts suggest applying variable frequency drives (VFD) to the equipment. VFDs can slow down the speed of the equipment, helping to reduce energy costs and extend the service life of the equipment. But VFDs can also easily ramp up the freezer or cooling equipment if it is at full load. For example, VFDs on condenser fans can control the floating head pressure. Lowering the floating head pressure via the VFD reduces the energy consumption for the condenser fan motors and compressor motors. VFDs can also improve overall efficiency on other areas of a refrigeration system, including evaporator fan motors and pumps.

VFDs can also help manufacturers cool or freeze various products by modifying the airflow for each product. For example, if a processor freezes thick half-pound hamburger patties, it can’t use the same velocity of airflow to freeze thinner sausage patties because the airflow would blow the patties off the conveyor. With a VFD, an operator can easily adjust the speed of the fan to freeze the patties at the proper velocity, speeding up changeover. “The benefit of a VFD is that it can regulate the airflow, so it doesn’t blow product all over the place,” says Paul Osterstrom, senior vice president of marketing and sales for Advanced Equipment Inc., a supplier of freezers and chillers based in Richmond, British Columbia, Canada. “VFDs make the machinery more flexible for whatever product you’re running.”

“This is something we encounter more and more because our customers are running many different products in one freezer. It’s sometimes 10 to 20 different products, and they don’t need the same airflow,” says Mathieu Nouhin, product manager at Dusseldorf, Germany-based GEA. “We add frequency inverters on the fan motor so we can optimize the airflow for product, selecting the right speed for the fans and then saving energy, too.”

On the safe side

recirculating CIPMany types of cooling and freezing equipment use recirculating clean-in-place (CIP) systems, which clean the equipment multiple times and recycle the cleaning solution during the CIP process. It ensures thorough cleaning and saves on water consumption.Photo courtesy of Advanced Equipment Inc.Manufacturers are also requesting more food safety features from their industrial refrigeration equipment. For example, suppliers are designing their equipment with nonhollow structures and welded construction. Unlike equipment that uses bolted construction or caulked joints, welded construction does not have harborage points for bacteria to grow. In addition, some manufacturers are elevating their industrial refrigeration equipment off the floor with fully-welded pins rather than plates, which can trap dirt and bacteria. And freezing and cooling equipment today often has open profiles to allow workers to easily access and clean it.

According to Osterstrom, the design and materials of the freezing and cooling equipment are key to ensuring food safety: “If you don’t have a freezer designed to be cleaned properly, it really doesn’t matter how good of a CIP (clean in place) system you have. If you don’t design a way that prevents food from being trapped and reduce the number of welds, reduce any of porous structure, or reduce bolts and those types of things, then it really still doesn’t get clean. So it is a combination of a CIP system and a freezer that is designed for cleaning.”

Suppliers are augmenting the CIP features of their freezing and cooling equipment. For example, GEA and Advanced Equipment offer recirculating CIP systems, which clean the equipment multiple times and recycle the cleaning solution during the CIP process. The solution is filtered before it is reinjected back into the equipment for further cleaning. This CIP system ensures the equipment is cleaned thoroughly without using inordinate amounts of water, resulting in significant water savings.

Some manufacturers like meat processors require an extremely high level of hygiene, so they use heat treatment or pasteurization systems in conjunction with CIP. After the CIP process is completed, the heat system raises the temperature inside the cooler or freezer to about 170°F to kill any remaining pathogens that the CIP system may have missed. However, the heat treatment is only effective for freezing and cooling equipment that use welded construction.

“This is only possible with fully welded enclosures,” Nouhin says. Some freezer providers use insulated panels, which are assembled with caulked joints, he states. “These caulked joints can resist a maximum temperature of 140°F, which means you cannot reach the pasteurization temperature. But with the fully welded enclosures, there are no caulked joints or silicone joints. So we can increase the temperature and reach the pasteurization temperature of 170°F to make sure all the bacteria are killed.”

Manufacturers are also turning to automation to strengthen their food safety protocols and comply with food safety regulations. Sensors, programmable logic controllers, and other similar Internet of Things devices allow operators to ensure consistent temperature control and continuous temperature monitoring. In addition, automation incorporated into freezing and cooling equipment records and stores data that manufacturers need to verify to regulatory agencies they are meeting food safety guidelines.

“As food safety becomes more and more stringent, the requirements for the refrigeration systems to operate properly and maintain proper temperatures are also becoming more and more stringent,” Pipkin says. “So computer control programs and data logging have become very important not only for processing, but for the refrigeration system as well.” Manufacturers have an obligation to maintain that data for long periods of time to prove that they’re following procedures, regulatory requirements, and good manufacturing practices, he adds.

CALLIFREEZE with French friesCALLIFREEZE from GEA uses sensors to monitor the condition of products exiting the freezer and then automatically calibrates the freezer’s parameters to ensure products in the freezer are frozen based on optimum requirements, including air temperature and retention time.Photo courtesy of GEA.GEA uses CALLIFREEZE sensors in its freezer line to monitor the condition of products exiting the freezers and then automatically calibrates the freezers' parameters to ensure products are frozen based on optimum requirements. The control system continuously monitors the level of crystallized water in the food and then automatically adjusts product retention time in the freezer, air temperature, and fan speed to achieve the precise level of freezing required with minimum energy consumption.

With traditional freezers, operators typically pull a random batch of product off the line to measure the temperature. Because the products are usually frozen completely, operators are not able to insert temperature probes into them. So they measure the freezing temperature between the products.

GEA uses a sensor that automatically and continuously measures through the product and gauges its level of frozenness and temperature, Nouhin says. “We now have an inline measurement that provides accurate information and trust about the product’s frozen quality at the exit of the freezer. And we can also use this sensor to control our freezer to make sure that the freezer parameters are adjusted to match the target requirements.”

With CALLIFREEZE, processors can monitor product continuously, says Nouhin. “This improves food safety because they can make sure the product delivered from the freezer meets the [temperature] targets that they set up for that process.”

Green concerns

Beyond enhancing food safety, many manufacturers want their freezing and cooling equipment to help them reduce their environmental impact, prompting them to consider the best refrigerants. Cost-effective synthetic refrigerants, such as chlorofluorocarbons and hydrochlorofluorocarbons, have fallen out of favor because of their high global warming potential (GWP). Many safety and environmental agencies encourage manufacturers to use natural refrigerants, such as carbon dioxide, anhydrous ammonia, and propane, because they don’t harm the environment and have little to no GWP and ozone depleting potential.

“We typically suggest keeping natural refrigerants as viable options because of the longevity that we’ve seen with natural refrigerants,” Pipkin says. “We’ve gone through three decades now of bans on manmade refrigerants, and it seems the list of available uses are getting smaller and smaller, whereas natural refrigerants, especially CO2, ammonia and propane, are still commonly in use today.”

Ammonia remains the most popular natural refrigerant choice among manufacturers. It is an abundant, low-cost natural resource that offers superior thermodynamic properties. Because it can absorb large amounts of heat as it evaporates, manufacturers can use less ammonia to achieve the same level of performance as other refrigerants as well as use smaller, thinner pipes and components. However, ammonia is also highly toxic and flammable, which is why it is subjected to numerous regulations by government agencies, including the Occupational Safety and Health Administration and Environmental Protection Agency.

To mitigate the risk of ammonia exposure to workers and reduce the amount of ammonia used in freezing and chilling equipment, some manufacturers are using ammonia-carbon dioxide cascade systems. A cascade system circulates ammonia and carbon dioxide through their own independent compressors, circulating the refrigerants around separated circuits. The two circuits are connected by a heat exchanger called a cascade condenser. The ammonia runs through the high-temperature circuit, while carbon dioxide flows through the low-temperature circuit. This configuration allows for the ammonia charge to be limited to the machine room, while carbon dioxide is present in the processing and storage areas and can be piped to other parts of the plant.

low-charge ammonia systemFRICK’s Low Charge Central System uses remote distributed condensing units to minimize liquid ammonia. It distributes only vapor ammonia throughout the plant. The ammonia vapor is only condensed to liquid at the point of use.Photo courtesy of FRICK.Another safe and environmentally-friendly alternative to a traditional two-stage ammonia-only system is a low-charge ammonia system, which uses ammonia in very low volumes. For example, FRICK’s Low Charge Central System (LCCS) helped Congebec, the largest refrigerated service provider in the province of Quebec, Canada, minimize its ammonia charge by 80%. LCCS minimizes liquid ammonia by distributing only vapor ammonia throughout the plant. The ammonia vapor is only condensed to liquid at the point of use. There is no liquid ammonia in the engine room, and it only exists in the plant in close proximity to where it is needed. The system drastically reduces the amount of ammonia in the refrigerated space, which reduces potential product damage and ammonia leaks that can harm workers.

“We’re not moving liquid all over the facility. We’re only moving vapor. So we’re interconnecting everything with vapor lines instead of liquid lines,” explains Nevin Forry, senior product manager for FRICK. “We condense close to the point of use, we store only a very minimum amount of liquid at those points, and then we use low-charge technology for evaporators. We’re using direct expansion evaporators, which means that we’re not having a lot of liquid in the operating evaporators.

“And then we’re just moving vapor from point A to point B, back to the compression room,” he adds. “So the compression room is what we consider to be a central system, and then we’re keeping our liquid to a minimum out of those remote locations.”

The big chill

While most manufacturers use mechanical refrigeration, like low-charge ammonia systems, cryogenic refrigeration is another eco-friendly option that doesn’t use any ammonia. Mechanical refrigeration uses refrigerants to cool coils to lower the air temperature. That chilled air passes over the food products to remove heat from them. With cryogenic refrigeration, on the other hand, food is sprayed with or immersed directly into liquid nitrogen or carbon dioxide. The food is frozen or chilled almost instantly.

Cryogenic refrigeration has many benefits over mechanical refrigeration. As refrigerants, nitrogen or carbon dioxide have negligible environmental impact. In addition, cryogenic refrigeration can reach substantially colder temperatures and chill products much faster than mechanical refrigeration. For example, mechanical freezing can get to as low as -40°F. Cryogenic freezing can go as low as -160°F with liquid nitrogen and -80°F with liquid carbon dioxide. That type of rapid freezing significantly reduces dehydration or freezer burn, thus protecting the texture and flavor of the product.

“If I can freeze something faster, it means I’m going to get smaller ice crystals, which means a higher quality of product,” says Scott Robertson, North America food industry manager at Air Products, an industrial gases company based in Allentown, Penn.

Cryogenic refrigeration also has lower upfront costs. The purchase and installation of equipment is inexpensive and takes up less floor space compared to mechanical refrigeration equipment. But cryogenic refrigeration requires large volumes of refrigerant, an ongoing, costly expense.

Wolverine Packing Co., a meat processor in Detroit, has already seen return on investment since it installed two cryogenic bottom injection (BI) chilling systems from Messer, a Bridgewater, N.J.-based company that supplies industrial gases and freezing and chilling equipment for the food industry. The processor uses the system to mix its ground beef product prior to grinding and forming patties. The system injects liquid nitrogen from multiple points at the bottom of Wolverine’s twin mixers, leveraging the thermodynamic properties of the nitrogen. The nitrogen starts chilling the product the moment it is injected and continues to chill it as it disperses and blends with the food product. According to Riley Cronk, production planner at Wolverine, the BI system chills the temperature of the meat between 29°F and 31°F, the ideal temperature range for forming patties, about 30 seconds faster per batch than the company’s previous chilling system.

Wolverine previously used a carbon dioxide cryogenic chilling system that worked fine until the company had to increase production. When the liquid carbon dioxide was injected into the meat, Wolverine had to give the cryogen enough time to sublimate. But as production demands grew, the company didn’t have the time to wait for complete sublimation. So the fine carbon dioxide particles turned into moisture rather than gas, trapping moisture in the meat. That created a red liquid and air leaking from the meat in the package.

When Wolverine switched to the BI system, it didn’t have to wait long for sublimation to occur with the nitrogen after blending. As a result, the new BI system is helping the company gain 50 minutes more of production time daily, or three to five batches more per day. That equates to an extra 30,000 lb of ground beef patties a day.

“We don’t have quality packaging issues any more,” Cronk says. “We don’t have to worry about CO2 snow getting trapped in the meat and causing quality issues, and it just speeds up our entire process. That’s a huge benefit. Gaining that extra 30 seconds per batch was very helpful.”

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