Cooling Efficiency Ratio

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Cooling Efficiency Ratio

Is the new indicator a valid KPI for the air conditioning market?

The Cooling Efficiency Ratio (CER for short) has increasingly been discussed as a key performance indicator in the refrigeration and air conditioning industry for several weeks. Where does this new indicator come from and what does it reveal?

The CER has been defined as part of the development of DIN EN 50600 (standard for the equipment and infrastructure of data centers) and documented in EN 50600-4-7. It is intended as an indicator for classifying and reviewing the effectiveness of data center cooling systems.

In this process, the variables
Q(removed) = the total amount of heat removed from the data center (annually) in kWh
and
E(cooling) = the energy consumption (annually) of the cooling systems in kWh are used as follows to calculate the CER:


It is essential that both Q(removed) and E(cooling) are measured in kWh for the same period of time (T).

The formula now shows us relatively clear that the effectiveness of cooling can only be specified in relation to a defined data center. The industry must not make the same mistake it made some time ago with the PUE (Power Usage Effectiveness) and use the CER to evaluate insulated air conditioning systems or individual refrigeration units.

Similarly to the PUE, the CER is only suitable for measuring the efficiency of a cooling system in a real data center environment or installation. It cannot be applied to a component or infrastructure. To illustrate this once again – the CER only relates to the efficiency of the cooling system in a defined data center; the PUE relates to the efficiency of an entire data center. Even if the CER is not a suitable indicator for evaluating individual air conditioning units/systems, another key performance indicator has been introduced that further emphasizes the importance of the issue of energy efficiency in data center cooling – and this may contribute to increased market awareness.

To illustrate this once again – the CER only relates to the efficiency of the cooling system in a defined data center; the PUE relates to the efficiency of an entire data center.

Even if the CER is not a suitable indicator for evaluating individual air conditioning units/systems, another key performance indicator has been introduced that further emphasizes the importance of the issue of energy efficiency in data center cooling – and this may contribute to increased market awareness.

About the author

Benjamin Petschke was born in 1969 in Germany. After studying physics he joined STULZ in 1996 and worked since then in the R&D, Export and Marketing department on different positions. With 19+ years’ experience in the Data Center cooling industry, Mr Petschke is specialised in Data Center cooling design, energy saving and acoustic issues.

He works closely with the Joint Research Centre of the European Commission for the Code of Conduct on Data Centres on the Best Practice section and recently with the German DKE in development of the DIN EN 50600, Information technology – Data Centre facilities and infrastructures.

Mr Petschke authored White Papers on subjects like Best Practice for Data Centre Cooling and Indirect Free Cooling with Dynamic Control Logic.

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