Getting cooler is more than a flick of a thermostat dial

July 19, 2000
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WASHINGTON, DC — When the government ordered that refrigerated display case operating temperatures drop to 41°F, manufacturers knew there was more to that than just dialing back the thermostat a few degrees.

The government was responding to concern for food safety. Manufacturers faced the task of meeting the more stringent temperatures without increasing in-store energy costs. Part of the solution has involved, at times, rather extensive redesigns, said Joseph Humphrey, chairman of the Technology Committee of the Commercial Refrigeration Manufacturers Association.

He outlined the challenge to an audience of supermarket engineers and technicians during the annual Food Marketing Institute Energy & Technical Services Conference, held here recently.

Just dropping temperatures from the previously acceptable 45°F to 41°F adds approximately 4% energy increase for each 1°F lowered, said Humphrey. So, some of the solutions the industry has been looking at include changing the lighting within the cases so that it still displays products properly but gives off less heat, and exploring the use of secondary fluids as a way to improve evaporator temperatures and allow for faster defrost.

Objectives in the redesign included:

  • Improving efficiency by raising evaporator temperature.

  • Better temperature distribution within a refrigerated zone through tighter temperature spread and the elimination of shelf variation.

  • A more efficient product development process that incorporates more computer flow dynamics and thermal imaging.

Piggybacking onto this effort was research done by Southern California Edison. One of its engineers, Ramin Faramarzi, reported on some of its findings involving a comparison of an older case with fluorescent lamps and electronic ballast, and a newer case using high-efficiency coils and an electronically commutated motor.

He said old cases have greater heat gain from the lights, fans, radiation, and infiltration of outside air. In the situation of one of the newer cases tested, there was high conduction load due to less cabinet insulation. He added, though, that the new case “was less vulnerable to ambient changes than the old case, probably due to a more effective air curtain design which resulted in less infiltration of room air.”

Further, he said “the new case had a 31% lower cooling load and 34% lower compressor power requirement.”

He noted that in situations where there was cooler and drier store air, cooling load dropped.

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