Consider closed-cycle air refrigeration (CCAR). A few years ago, CCAR was viewed as sufficiently promising for flash freezing in food processing to warrant a $2.1 million development grant from the U.S. Department of Commerce's Advanced Technology Program. Dry air pressurized to 1,200 psi serves as the refrigerant. The technology has the ability to chill products cost effectively at temperatures ranging from -60°F to -150°F. Cooling costs are pegged at half that of cryogenic flash-freezing systems with which CCAR competes.
Based on a successful pilot application, a 62-ton, skid-mounted CCAR unit with a 12-ft. by 40-ft. footprint was fabricated by Air Products Inc. and Toromont Process Systems Inc. "The system works very well, though it takes a fairly expensive product to justify getting down to that temperature range," notes James Shepherd, a manager in Toromont's Houston office. "It's small, runs very smoothly and relatively quietly because the expander/compressor is the only moving part, and the closed cycle is very dependable, unlike the open-cycle systems that were tried." Unfortunately, no CCAR systems have been installed in the four years since the commercial technology was proven.
The concept of air as a refrigerant is valid, nonetheless, and consistent with the intent of the Montreal Protocol and other initiatives to address greenhouse gases and other environmental issues. "The future is going to be in natural refrigerants-carbon dioxide, ammonia, even air and water," believes engineer Ronald P. Vallort, chairman of the International Institute of Ammonia Refrigeration and principal of Ron Vallort and Associates in Oak Brook, Ill. "The use of those refrigerants has the potential to lower power consumption, even in a 1,000-ton system."
While domestic energy costs discourage application of high-efficiency innovations in refrigeration, U.S. food companies are applying those principles in new plants being built in Asia, South America and elsewhere, he says. And energy-conscious Europeans are bringing their efficiency penchant to the new plants they're building on U.S. soil. The world's largest food company provides an example.
The Arkansas cascade"Our energy costs aren't high enough to encourage processors to apply concepts like absorption chillers, but they will be," says Vallort. "There are some exceptions: Nestle is a company that is looking long term and applying these technologies. They're not looking at the cost of energy today. When costs increase, they'll be prepared."
The most notable Nestle refrigeration initiative involves the recently completed Jonesboro, Ark., facility, a 525,000-sq.-ft. production and refrigerated warehouse complex for the company's Stouffer's frozen goods line. A cascade system that combines ammonia refrigeration with a secondary loop using carbon dioxide as the refrigerant in production areas was deployed. The system was installed by The Stellar Group, which believes it is the largest CO2/ammonia cascade system in the world.
Cascade systems take advantage of CO2's higher saturation pressure than ammonia, which helps it maintain positive pressure at temperatures in the -25° to -65° F range. Pressure loss of 5 psi or more occurs between the evaporator and machine room in a large plant, and CO2 exhibits much less temperature loss when pressure drops than ammonia. It also requires much smaller piping and evaporators and operates at pressures three or more times higher than ammonia.
Europe boasts the greatest concentration of cascade systems, and food companies there now are waiting to see how the technology performs for the early adopters before taking the plunge themselves, according to Ingmar Pahlsson, product line manager with Helsingborg, Sweden's Frigoscandia Equipment. "In most cases, ammonia is the best refrigerant," he believes, though CO2 may be 10 to 15 percent more energy efficient for low-temperature applications, helping offset the system's higher capital costs. The primary driver in deploying them, however, is a desire to get ammonia out of production areas. In the event of a leak, human hysteria remains a significant danger, despite ammonia's low lethality risk.
"Nestle wants to use natural refrigerants whenever they can, and that includes CO2," says Pahlsson. With that sentiment growing, Frigoscandia is rolling out a CO2 version of its low volume system (LVS) for ammonia. LVS uses a two-phase flow that lowers system pressure and circulates more refrigerant than conventional systems, allowing compressors to run at lower temperatures. LVS is particularly well suited for installations in existing buildings: the dry return and absence of a pump allow refrigerant to move upward toward compressors, rather than in a constant downward slope.
"Unless there is a spill, ammonia systems are the most environmentally friendly refrigeration option," believes Rob Reifsnyder, national engineering manager-facilities for Nestle Waters North America. The division operates 22 plants, with two more coming on line early next year. The new units, as well as an Ice Mountain plant in Mecosta Township, Mich., built last year, adhere to the United States Green Building Council's Leadership in Energy and Environmental Design principles.
"Economic payback is not immediate on ammonia because of the capital costs," allows Joe Labrie, Nestle Waters' senior design manager of process and utility systems, "but we're doing it because it's the right thing to do." Michigan's chilled water for process cooling and HVAC load comes from outdoor units, an approach that "takes our chilled water electrical costs down to zero during the winter," he adds.
Absorption chillers were incorporated into the design of a new California plant, with waste heat from reciprocating compressors and exhaust stacks helping cool the facility. "You need an electricity price of perhaps 10 cents a KW hour to create a system that is economically justifiable," Reifsnyder points out, and California's high energy costs provide one of the few opportunities to deploy such a system.
Up on the roofBecause of the intense scrutiny of the sanitary aspects of food plants, penthouse refrigeration units are growing in popularity. "For ready-to-eat meat processors, the norm is becoming the roof-top unit," says The Stellar Group's Chuck Taylor. Hinged fan panels and drain pans are being incorporated to facilitate washdown. Desiccant systems are being married to refrigeration units to lower the humidity that bacteria and mold need, adds Taylor.
Sanitation also is improving thanks to reductions in the price of stainless steel, points out Orlando Negrin, head of St. Onge, Ruff & Associates' refrigeration engineering department. Stainless steel coils are replacing coils made of hot-tipped galvanized steel. Stainless steel tubing is thinner, corrosion resistant and transfers heat faster, which means less work for compressors.
Control technology is enabling processors to improve efficiency and reliability. "The electronics side is moving faster because the payback has fallen to two or three years, compared to seven or eight years a few years ago," Negrin says. "With the data that controllers give them, companies are finding that they can increase the temperature in their freezers 15 degrees and not have a negative impact on product quality."
"We're seeing a lot more sophisticated controls to maximize freezer efficiency," agrees Taylor. If manual collection of data was required, trend reports that help plants minimize defrost cycles and manipulate loads to take advantage of off-peak electricity costs would be difficult to generate.
Sophisticated, affordable controls are not limited to ammonia systems. Small and mid-sized processors using hydro-chlorofluorocarbon refrigerants are taking advantage of microelectronics, as well. An example is the Beacon II Smart Controller, which has much of the functionality of customized control systems. "Others have caught up, but it was the only advanced remote monitoring system available for smaller freezers when we installed it," recalls Jim Johns, owner of J&S Dairy, a Traverse City, Mich., distributor. J&S built a 4,000-sq.-ft. freezer with six 22-horsepower refrigeration units in April 2001. Besides dairy products, the company handles Ben & Jerry's and other premium ice creams. Johns can monitor freezer temperatures and performance from his office or home.
"Some supermarkets have comparable microprocessor controllers that cost thousands of dollars; this is in the hundreds of dollars," says Ray Clarke of Heatcraft Refrigeration Products, a Lennox International unit that designed J&S's condenser/evaporator/controller package. Each controller can manage up to four refrigeration units. It logs seven operating parameters in a seven-day cycle, with a download port to a dedicated PC.
"Conventional refrigeration systems of this size usually are set at four defrosts a day," Clarke says. "We're seeing a reduction to one a day, with none on the weekend."
Another trend in smaller plants is adoption of glycol systems, often as a replacement for CFC. The shift is most pronounced in bakeries, where glycol is becoming the preferred refrigerant in dough mixers, according to Rolf Tseng, a mechanical project engineer in Lockwood Greene's Atlanta office. The expansion valve in Freon-based direct-expansion systems can be a chronic problem, requiring periodic adjustment and frequent servicing, he says. "Glycol is relatively expensive, but there is very little replenishment needed, there's less maintenance, and it is very accurate in holding dough temperature to the recipe," says Tseng.
Nontoxic alternatives to ethylene glycol and propylene glycol are coming into the market. An example is Thermera, a betaine/water solution developed by Finland's Fortum Oil and Gas. Betaine is a byproduct of sugar beet processing. Cold flow characteristics are superior to propylene glycol, resulting in reduced pump demand, and technical performance that meets or exceeds industry standards.
Thermera is one of numerous renewable refrigerants that will emerge in the coming years, refrigeration engineers predict. Those innovations and the particular needs of the food industry keep refrigeration science fresh. As Tseng observes, "Refrigeration is old technology, but there is some art to system design because there are many different ways to accomplish a single purpose." That dynamism and the influx of technological refinements help warm the hearts of refrigeration experts.
For more information:
Dietmar Gamm, Air Products and Chemicals Inc., 610-481-3449, firstname.lastname@example.org
Janne Jokinen Lic, Fortum Oil and Gas, 011-358-10-4511, email@example.com
Ray Clarke, Heatcraft Refrigeration Products, 770-465-5712
Rolf Tseng, Lockwood Greene, 404-818-8679
Orlando Negrin, St. Onge, Ruff & Associates, 717-854-3861
Chuck Taylor, The Stellar Group, 904-923-0091, firstname.lastname@example.org
Jim Shepherd, Toromont Process Systems Inc., 281-345-9300
Ronald Vallort, Ron Vallort and Associates, 630-784-3821
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