DEFRA Manufacturing Sector
Information on other operations linked to refrigeration energy use in the Manufacturing / Production sector are available on this page.
Immediately loading a hot cooked food into a chiller or freezer imposes a very high heat load on the refrigeration system. Using ambient air to cool the food for a short time before loading can substantially reduce the energy consumption of the chiller or freezer without a significant increase in overall cooling time. The microbial safety is not compromised by a controlled ambient cooling stage.
Immediately, after cooling the rate of water evaporation from unwrapped foods is very high. A short period of ambient cooling will reduce the amount of moisture condensing on the evaporator coil when the food is put in the refrigeration system. This will reduce the need for defrosts and the extra energy consumed in the process. In addition condensation on the surface of any cold food in the chiller or freezer will be substantially reduced.
The biggest energy savings can be achieved with small cooked individual products such as chips, pies, sausage rolls, quiches and chicken pieces or shallow trays of fillings, gravies and sauces. In general additional space will be required for an ambient cooling stage since the overall cooling process will be longer than in a totally refrigerated process.
This may limit the use of ambient cooling in existing food factories if space is limited. However, if height is available a spiral ambient cooler can often be utilised. When designing a new factory, space for ambient cooling can be built into the production line and the benefits of ambient cooling fully utilised.
Substantial energy saving can be achieved with ambient cooling. In the example shown, heat loads reduced by 49% with an ambient cooling stage of 1 hour at 20°C while the total cooling process was extended by less than 0.5 hours.
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Tips for Energy Saving in Meat Chilling
A detailed study of electrical energy consumption of all the refrigeration processes in a red meat abattoir and cutting plant has been carried out over a three month period. The primary chilling of meat immediately post-slaughter was the process that used the majority of the electrical energy in the plant. It used more energy than the sum of all the other refrigeration systems. Simple measures to reduce energy in primary chilling included closing chill room doors, maintaining door seals, switching off fans when not required, general optimisation of existing refrigeration plant and repair of faulty components.
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Food Chilling and Freezing
Correct refrigeration system choice is a vital part of selecting an efficient freezing or chilling system for long-term use. A 30-year operational life is not unusual. The size of the refrigeration system will vary according to the amount of heat that needs to be removed and ideally the heat load should be minimized. In cooling or freezing heat will be removed from the product and heat will also be introduced via transmission across structures, infiltration through doors and openings and from lighting, defrosts and people and machinery. In batch chilling and freezing systems the peak cooling duty will only be required for 10 to 15% of the process. The refrigeration therefore has to be designed to operate efficiently at part load. In existing systems the majority of short term energy savings are likely to be achieved through process optimization, replacement of key components and improved control i.e. speed control on fans. However a few new technologies and some older ‘niche’ technologies may save substantial amounts of energy. These include ambient cooling, perfusion, hot boning, immersion, evaporative cooling, impingement and heat pipes.
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Case study: Pie cooling
The cooling of hot products utilising air blast chillers is one of the most common refrigeration processes in the food-manufacturing sector. A specific study has been carried out on the cooling of pie fillings however the findings are equally relevant to the manufacture of ready meals and any hot solid/liquid food products. The study showed that to extract 75 kWh of heat energy from a tonne of hot pie filling the chilling system used between 147 and 208 kWh. The inefficiency was due to a combination of poor system design, poor control and operational practice. The energy saving potential of alternative cooling methods was then considered. In many cases there are alternative cooling methods, which are practical and are likely to be more energy efficient.
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Case study: Pie filling cooling
A study has been carried out of the pie filling air blast chilling operation at a pie manufacturing plant in the UK. The aim of the case study was to provide data on energy consumption in the air blast chilling of hot solid/liquid food mixtures (specifically pie fillings) post cooking under real use conditions in a manufacturing environment. The detailed data was also required for verification of the LSBU/FRPERC refrigeration model, which required trials under more controlled conditions (not seen during normal production).
The mean energy coefficient (EC) of the air blast chilling process was 0.44, which is poor compared to values up to 1.5 for forced air coolers as published in 2001. The predicted rate of temperature fall, using the refrigeration model, closely followed the measured data. The maximum difference between the predicted and measured mean centre tray temperature at any time is 5.9°C, the average difference is 2.3°C.
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Case study: Liquid pressure amplification of refrigerant in milk cooling application
The dairy sector is one of the major refrigeration energy users in the food industry. Significant energy and financial savings can be achieved by adopting new refrigeration technologies and practices. One such technology which has been available on the market for direct expansion evaporator vapour compression systems for a number of years but has not as yet found wide application is Liquid Pressure Amplification (LPA). This case study considers the application of a LPA and liquid injection to a cold store at a dairy plant in Northern Ireland. Before the application of the technology the cold store had difficulty maintaining temperature during periods of high ambient temperatures, with a drift of 5°C from design. The main aim of the case study is to investigate the performance of the LPA technology as installed at the plant and estimate the energy savings and environmental performance of the system.
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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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