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Using a standard two stage ammonia refrigeration system to model the impact of evaporative temperature on system efficiency, a study conducted for the British Frozen Food Federation identified energy saving opportunities of 4,800 tonnes CO2 per year in total from 13 food manufacturers and logistic service providers.

The “Improving The Energy Efficiency of The Cold Chain” study, managed by the British Frozen Food Federation with support and funding from the Carbon Trust Networks programme, considered the potential to reduce energy usage and CO2 emissions by managing operating temperatures more effectively.

Eight food manufacturers and five logistic service providers that represented large, medium and small companies manufacturing a wide range of frozen food products were provided with data loggers to monitor the temperature in pallets of food held in manufacturer cold stores, being transported and then being held in cold stores belonging to logistic service providers.

Modelling the refrigeration system

A standard two stage refrigeration system of the type used by the project participants has been modeled to identify the impact of evaporating temperature (TE) on system efficiency. The refrigeration cycle was modeled based on a set of standard parameters. These include:

• Two stage cycle, with optimum interstage pressure
• Refrigerant: ammonia
• Compressors: 75% isentropic efficiency
• No superheat or sub cooling
• Average condensing temperature (TC) of ammonia TC = 22oC
• 1000kW cooling duty

Using these assumptions, calculations showed how sensitive the efficiency of a refrigeration plant is to falls in TE and the even more significant extra compressor volume required as TE falls because of the decreasing density of ammonia.

Key areas of opportunity to improve cold chain efficiency

Eight key areas of opportunity to improve cold chain efficiency equivalent to 4,800 tonnes CO2 per year were identified at the host sites. These opportunities, which can easily be replicated at many sites in the UK, including frozen / chilled food manufacturer sites and cold storage sites, include:

• Raising cold store air temperature
• Reducing temperature difference between store and surge drum
• Adjustment of suction pressure to suit conditions
• Avoiding cold store air temperature fluctuations
• Separating blast freezers and cold stores
• Avoiding over-cooling in blast freezers
• Using variable speed evaporator fan control
• Using a flexible and effective defrost system

In addition, the study noted that the lack of electricity sub-metering on refrigeration systems is a key barrier to the identification of good energy saving practices.

About the British Frozen Food Federation

The British Frozen Food Federation is the leading Trade Association that promotes and protects the interests of the Frozen Food Industry.