Actions for Refrigeration Efficiency

• The most common maintenance/design related issues which result in higher energy bills and carbon emissions are shown below.

• Many of these issues do not become apparent until they impact on temperatures.

• By then thousands of pounds have been wasted on energy.

• Issues

• Dirty condensers

  • Reduces airflow through the coil 

  • Results in high discharge pressure - reduces efficiency. 

  • Simple visual inspections show whether the coils require cleaning.

  • If the condensers are a W arrangement check the entire heat exchanger.

  • Note that some areas may difficult to access and are often ignored.

  • Potential 5-10% reduction in efficiency.

• Incorrect condenser drain pipework 

  • If a liquid receiver is installed it should be piped in such a way that refrigerant can drain into it from the condenser by gravity (see diagrams below).

  • If it is piped incorrectly refrigerant can become trapped in the condenser.

  • The load on the compressors is increased which reduces efficiency.

  • Potential 10% reduction in efficiency.

• Low refrigerant level

  • Often goes undiscovered until the middle of the summer when the plant can no longer maintain temperatures. 

  • Watch the sight glass in the refrigerant liquid line to the evaporator.

  • If a constant stream of bubbles are visible refrigerant levels should be checked. 

  • If a low level is discovered the leak should be repaired and the correct refrigerant charge added.

  • Potential10-30% reduction in efficiency.

• Poor temperature control

  • Watch compressor operation. 

  • Compressors are controlled to maintain a constant evaporating temperature.

  • In a liquid chiller this is typically be 5°C lower than the liquid flow temperature, or 10°C lower than the space temperature in a coldstore.

  • For every 1°C lower than these temperatures you are typically losing 2-3% efficiency.

• Compressor sequencing

  • Constant cycling of compressors (more than 8-10 times per hour) results in drastically increased mechanical wear.

  • If compressors switch on and off very frequently re-commission your controls 

  • Consider fitting an inverter to control one compressor.

  • This will reduce cycling and ensure accurate temperature control.

• Evaporator frosting

  • Caused by:

    • poor door management (the ingress of warm moist air freezing on the evaporator), 

    • incorrect defrost settings or

    • a combination of both.

  • Potential 5% reduction in efficiency.