Milk cooling: Refrigeration system maintenance

A look at the key components of the refrigeration system, how to look after them and the likely energy and cost savings that can be achieved by robust yet simple maintenance.

Refrigeration system efficiency is highly variable from one installation to the next and from one month to the next. These differences can be attributed to changes in ambient conditions although they are often caused by different levels of maintenance.

A refrigeration system has a number of major components all of which must be working at their best for the whole system to do its job in the most efficient way.  Key components and how to look after them are:

• Condenser coil – this is the ‘outside coil’ (the radiator?) which gets hot and is used to dissipate the heat from the cooling process.  It must be clean and in good condition and positioned in a cool and shaded place. Many coils end up being blocked with dust and some are in the sun or in hot lofts.  Badly maintained and positioned coils are a major cause of low efficiency. Ventilation is also highly important. The coils must be fed with the coolest fresh air available and positioned to ensure no recirculation of warm air. Baffling the coils and shading them from direct sunlight to ensure this happens can make big improvements in cooling speed and efficiency.
• Refrigerant – the gas/fluid which transfers the heat around the refrigeration system. It can leak and a depleted refrigeration charge will cause the system efficiency to drop. Have the system refrigeration charge checked once per year by a refrigeration engineer..
• Expansion valve – this controls the amount of refrigerant which flows to the cooler and it must be set correctly for best operation – again this needs checking once per year by a qualified engineer..
• Condenser fan – this passes air through the condenser coil. It’s operated by a pressure switch in the refrigeration line and this must be set accurately.  Too low a pressure and the fan will operate too long, too high and the refrigeration efficiency will drop.  Check this at maintenance time, which should be at least annually.
• Refrigerant pipes – these need to be insulated to prevent energy loss prior to the refrigerant doing its work. Pipe insulation does degrade so it needs to be checked periodically.

Generally new refrigeration systems are more efficient than older designs. The use of scroll compressors, condensers and expansion valves has improved efficiency in some cases by more than 30%.  So an overall upgrade of the refrigeration unit can be a good investment, especially when equipment is being replaced.

The difference between a well maintained and appropriately positioned and ventilated refrigeration system and one which has blocked coils, inappropriately set controls and is badly ventilated can be as much as 40%.  The relatively low cost of simple maintenance is therefore a particularly good investment.  For a system cooling 1.6 million litres of milk per year savings can be as high as £500 per year, moving from lowest to highest efficiency.