United States. West Liberty Foods, a meat processor, uses four cold storage facilities located in West Liberty and Mount Pleasant, Iowa, Tremonton, Utah, and, since 2014, Bolinbrook, Illinois.
The Bolinbrook cold storage facility, managed by Liberty Cold Storage, uses much less ammonia than in older plants. It only uses 3.4 tons of ammonia to refrigerate West Liberty meats and a variety of third-party products, desserts, and other foods.
This facility has recently been expanded. It underwent an expansion of 11,427 m2 at the beginning of 2018. It now covers 23 537m2 and its ammonia load supports a capacity of about 3263 kW, with a ratio of only 1.04 kg ammonia / kW.
This amount of ammonia is below the threshold (4.54 tons) above which cold storage plants must comply with strict regulations set by the Environmental Protection Agency.
Liberty Cold Storage was able to maintain a low ammonia load by employing a direct expansion (DX) evaporator for medium and low temperature applications.
DX evaporators, which require much less ammonia than a supercharging system, have been used for medium temperature applications but not for low temperatures. However, Washington state-based Colmac Coil devised a design to make them work at low temperatures.
This system, called the "Advanced DX System" or "ADX System," could have used about 362 kilograms less ammonia if it didn't incorporate thermosiphonic oil cooling, but according to an ADX designer, this alternative would have been expensive.
The ADX system mainly reduces the ammonia load thanks to the patented design of the evaporator. According to Bruce Nelson, president of Colmac Coil, the inner surface of the evaporator tubes has a "wick structure," which produces "enough capillary pressure to make liquid ammonia completely cover the inside of the tubes," he said. "Otherwise, the liquid falls to the bottom of the pipe, with incomplete wetting."
The ADX designer compared the grooves inside the tubes to that of a rifle barrel, allowing ammonia to rotate 360 degrees along a tube like a rotating bullet, improving heat transfer.
The other part of the evaporator system that reduces the load is a distributor that optimizes the flow of ammonia through the tubes (circuits).
The technology behind this evaporator isn't really new, but Colmac Coil found a way to leverage it differently in the ADX unit to reduce the amount of ammonia needed, Watters said. According to Nelson, the ADX evaporator reduces the ammonia load in a supercharging system by 30-50 times.
According to Tim Cox, vice president of Liberty Cold Storage, by reducing the load of ammonia, the ADX system is easier to manage than a traditional system.
To improve system safety, most of the 32 evaporators used at Liberty Cold Storage are housed in penthouse enclosures on the roof of the building, blowing cold air through ducts in the cooling area (the exception is the dock area and a small cooler, using hanging evaporators). In this way, they resemble low-load packaged units, except that the latter contain all the cooling equipment, not just the evaporators.
In terms of cost, Tim Cow saw "a price advantage" with the ADX system being slightly less expensive (in equipment plus installation) than a liquid supercharging system. According to Nelson, what is helping to drive adoption of the ADX system is its lower cost, 2% to 5% less than that of a traditional supercharging system.
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