DEFRA Cold Storage Sector
Case Study: Cold store energy use and optimisation
Investigations at three UK cold storage complexes demonstrated significant opportunities for energy savings of at least 30% in the 5 stores examined. A survey of ammonia plants illustrated how a plant that was originally designed for efficient operation has altered over the years and now consumed approximately 43% more energy than originally intended. A two-stage ammonia plant with flash intercooler, pumped recirculation and evaporative condensers should be very efficient.
However, poor part load isentropic efficiency of the compressors, a lack of balance between high and low stage compressor capacity and the need for maintenance has turned what was an efficient plant into an inefficient one.
In cold storage facilities with direct expansion refrigeration systems, substantial savings could be achieved if operation was optimised in terms of heat loads on the rooms and the operation of the refrigeration system. Many improvements were low cost (improved door protection, defrost optimisation and repairs).
The most efficient cold store in terms of heat removed by the refrigeration system used a low-pressure receiver system. However, the plant used more energy per m3 of storage and this was due to it being a small store and also to the way the store was operated with high transmission, infiltration and fixed heat loads.
Improvements to its operation could be made by fitting better door protection and reducing fixed loads. Substantial improvements could be made to all cold stores by fitting better door protection and pedestrian doors, installing liquid pressure amplification pumps and suction liquid heat exchangers and by optimising defrost settings.
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Food Refrigeration and Process Engineering Research Centre (FRPERC), Grimsby Institute (GIFHE), Nuns Corner Campus, Laceby Road, Grimsby, North East Lincolnshire. DN34 5BQ. UK.
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