Energy Efficiency Ratio (EER)

The Energy Efficiency Ratio (EER) is a performance metric used to evaluate the energy efficiency of electrically powered cooling systems. It represents the ratio of the cooling output provided by a system to the electrical power required to produce it.

The higher the EER, the more efficiently the system operates at a given operating condition. For example, an EER of 4 indicates that a system delivers 4 kW of cooling output while consuming 1 kW of electrical power.

Calculating the EER

The EER is calculated by dividing the cooling capacity by the electrical power input:

EER = Cooling Capacity / Electrical Power Input

Because the EER is determined at a specific operating point, actual performance may vary depending on ambient conditions and system load.

EER vs. COP

While the Coefficient of Performance (COP) is commonly used to describe the efficiency of a heat pump in heating mode, the EER measures efficiency in cooling mode. Both metrics are based on the same principle: they compare useful thermal output to the electrical energy required to generate it. The difference lies in whether heating capacity or cooling capacity is being evaluated.

Relevance for industrial heat pumps

In addition to supplying process heat, industrial heat pumps can also provide process cooling in certain applications. The EER is therefore an important indicator of cooling efficiency and can support the design and evaluation of systems that utilize both heating and cooling. When heating and cooling are generated simultaneously, overall system efficiency is typically assessed using a combined COP, which relates the total useful heating and cooling output to the electrical energy input. This is particularly relevant in applications that simultaneously produce chilled water and hot water or steam at supply temperatures above 100°C (212°F).

Because the EER reflects performance at a single operating point, additional metrics may be used to assess efficiency under varying operating conditions. One example is the Seasonal Energy Efficiency Ratio (SEER), which accounts for fluctuations in load and ambient temperature over time.