An Engineering Extension energy feature
An Engineering Extension energy feature
By Tom Logan
In Faison, N.C., a group of producers, utility, state and research agencies has developed a produce precooler that benefits from off-season electrical rates and gains other economic benefits for growers.
The produce precooler operates on the same principle as cool storage. It makes ice year-round and stores it for use later in the harvest season to precool produce.
Precooling allows produce to arrive at its destination much fresher, which extends its shelf life. Longer shelf life means growers receive a higher return for their produce.
In California, Texas, and Florida, where growing seasons are much longer, growers are using the precooling technology extensively.
In North Carolina, the harvest period lasts only eight to 10 weeks. Before the technology of thermal storage was introduced, precooling wasn't cost effective due to the short growing season occurring at the year's peak electrical demand and corresponding high rates. Thus, the cooling system would need to have a high capacity to handle the large, short duration load. Growers could not justify the high cost to construct and operate such a system.
The produce precooler consists of a 20,000-pound-a-day ice maker that uses water from melting ice and a 3/4-million gallon underground storage reservoir made of concrete.
After producing ice, the system augers it back to the tank. In seven months, the precooler makes nearly five million pounds of ice.
The produce precooler even uses its waste heat. The ice maker provides moist heat to cure the sweet potato harvest and warm the packing line.
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