case study: Energy Efficiency in Cold Storage

Mr. Soon Jin Chew is a technical director at NRS Process Systems, one of our members. His work focuses on customers in cold chain logistics centers and investigates how optimum energy efficiency can be achieved in medium to large cold storage facilities in Southeast Asia. This provide NRS Process Systems with baseline data that makes it possible to benchmark efficiency improvements on other projects.

Differences in property size affect facility layout and so each cold storage facility is designed differently. This makes it difficult to carry out comparisons, but energy performance is assessed using the following parameters: load calculations, refrigeration plant design and operation.

Load calculations are the first step in determining the overall cooling load for the refrigerated warehouse and selecting the appropriate equipment. The load calculations include four parameters: insulation, air infiltration, product load and miscellaneous load. Generally, insulation and miscellaneous loads constitute a stable or constant load that may be accurately determined. However, air infiltration rates due to door opening frequency/duration and product throughput are usually “guesstimates”, so these load estimates tend to be conservative unless the client provides better input.

Once the total cooling load for the rooms is computed, the overall system design can be determined. Many options are available to the design engineer, who often seeks a balance between achieving energy efficiency and cost. The facilities layout will often have an effect on the refrigeration plant design. The chosen design may have an impact on the facilities operations and often requires a compromise, since available space and customer needs are the deciding factors. Finally, the operation of the refrigerated facility is another key element in achieving low power consumption. 

Mr. Chew has identified the following measures for improving overall efficiency:

1. Review the design cooling load calculations, especially in terms of daily product throughput, to ensure that they match the actual conditions and minimize the overall cooling load.

2. If the room temperature is stable, it is possible to increase the room temperature from -20°C to -18°C to improve the efficiency of the compressors (about 5 to 8% more efficiency).

3. Optimize product racks or storage systems to achieve a better kWh to stored pallet ratio.

4. Analyze traffic flows and door design/arrangement for different space types to reduce warm, moist air infiltration into the cool or cold space and minimize wet floors, walls or ceilings.

5. Use high-efficiency compressors, oil separators, and motors.

6. Ensure good air distribution within the room geometry in relation to storage racks.

7. Use electronics to collect data, trend key parameters and analyze to improve efficiency.

8. Assign experienced or trained personnel to operate, maintain and service the facility, including safety; this will help keep efficiency levels high.

Coordinating and maintaining the key areas will help provide the right equipment and optimize the efficiency of the facility.