Energy benchmarking in process refrigeration, although a complex process, has proved to be an essential tool for the enhancement of operational efficiency, according to Dr. Andy Pearson, the longtime Managing Director of U.K. OEM Star Refrigeration.
Pearson addressed this topic in a keynote speech on “Energy Performance of Process Cooling Equipment” at the 10th International Institute of Refrigeration (IIR) conference, held in Ohrid, North Macedonia, April 27–29.
“There are many excuses for not benchmarking but no reason to ignore the benefits,” said Pearson.
These findings, he said, underscore the potential of energy benchmarking as a key tool for identifying energy savings and driving efficiency improvements in process refrigeration systems.
To explain benchmarking, he explored various process loads and highlighted the unique difficulties faced when benchmarking energy performance. Several systems – including a liquid chiller, a batch chiller, freezers such as blast and spiral freezers and a flow chiller – were evaluated. Despite the diversity of these systems, they share common characteristics that can be harnessed to extract meaningful performance data.
Thanks to modern computing methods, a more comprehensive analysis is now possible compared to what was achievable in the past. Yet interpreting results requires caution, particularly when multiple process lines are linked to a central refrigeration plant or when this central plant also serves a traditional cold storage warehouse.
In one case study cited by Pearson, a spiral freezer is used for freezing pizza with a product flow rate of 800kg (1,764lbs)/h, operating for 12 hours per week. This amounts to a total throughput of 9.6 metric tons per week.
The spiral freezer is a part of the central ammonia (R717) plant, which also serves a 42,000m3(1,483,216 ft³) cold storage facility.
The specific energy consumption (SEC) of the cold storage facility is given as 19kWh/m3 (0.54kWh/ft3) per year or 15,346kWh per week. Over a four-week period, the total energy consumption of the spiral freezer and cold-storage facility is 127,333kWh or an average of 31,808kWh per week.
Based on this, the spiral freezer’s Product Energy Consumption (PEC) is calculated to be 171.5kWh per metric ton of processed pizza. However, the PEC for a freezer with high fan power and low COP is 148.1kWh per metric ton, indicating that there are potential areas for improving energy efficiency in this system.
Another case study mentioned by Pearson involved a blast freezer for meat products. The blast freezer and a 57,110m3 (2,016,820ft³) cold storage facility are served by a central ammonia plant. The SEC for this cold storage facility stands at 15.6kWh/m3 (0.44kWh/ft3) per year, translating to an annual total SEC of 890,916kWh.
The facility’s total annual energy consumption amounted to 2,940,060kWh. To identify the energy consumption specific to the blast freezer, the energy consumption of the cold storage facility was subtracted from the total, resulting in the blast freezer consuming 2,049,144kWh per year.
However, the blast freezer’s PEC was calculated to be 1,924.1kWh per metric ton of processed meat, noticeably more than the PEC best-practice figure of 222.2kWh per metric ton (representative of high fan power and low plant COP).