California Institute for Energy and Environment (CIEE)

The project objective was to implement evaporator fan speed modulation through the use of variable frequency drives and a new computerized control algorithm specifically designed for blast freezer control. An expected 55% to 65% reduction in blast freezer fan horsepower was expected resulting in an overall savings of approximately 35% to 45% in blast freezer combined fan and compressor electrical savings. The report discusses project approach to identify, select and install the variable frequency drive equipment, computer hardware and instrumentation, control software, and the development of a test apparatus to accurately measure product temperatures at various locations within the pallet of a blast freezer. The baseline and comparative blast freezing trials evaluated the relative product cooling performance of various fan speeds during different phases of product freezing in a blast freezing process. Cooling efficacy during the tests was measured by recording core product temperature at 12 different locations in a pallet layer of ground beef. Different combinations of fan speeds were compared to the baseline cooling performance. The fan constant speed set point used for the baseline was 100%. Tests were conducted based on 40 hour total blast cycle run times. The fan speed modulation tests were conducted by reducing the fan speeds at predetermined time intervals. The fan speed modifications achieve 71% fan energy savings and a combined fan and compressor energy savings of 39% for a 40 hour blast test. Shortening the blast cycle time to achieve a -10° F final product core temperature would result in fan energy savings of 77% and an overall refrigeration energy savings of 48%. The immediate benefit to California as a result of the project has been an average reduction of 1,621 kWh per blast freezing test trial or the equivalent energy to power 1,600 homes in California. The study results will strengthen efforts to promote the continued development of variable speed modulation technology to increase energy efficiency standards of batch style blast freezing cells typically found in the public refrigerated warehousing industry.