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Department for Business, Energy and Industrial Strategy

Refrigerated Air Dryers with Energy Saving Controls

1.1           Scope

Refrigerated air dryers are commonly fitted to compressed air systems to prevent moisture from condensing within pipe work and equipment. They work by cooling the air to a desired dew point temperature, thus forcing moisture to condense out of the air. This resulting condensate is then drained from the compressed air system.

A refrigerated air dryer typically increases the energy used in compressed air generation by between 2% and 5% depending on the type of product selected and how it is controlled. The pressure drop across the refrigerated air dryer is also a key factor in the amount of additional energy consumed as a result of the use of refrigerated air dryers. The aim of the Energy Technology List (ETL) Scheme is to encourage the purchase of higher efficiency models, which have low pressure drops across them.

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.2           Definitions

Refrigerated air dryers are products that are specifically designed to extract water vapour from industrial compressed air systems by means of cooling with a refrigeration cycle.

1.3           Requirements

1.3.1       Eligibility requirements 

To be eligible, products must:

  • Incorporate energy saving controls that automatically reduce the cooling output of the refrigerated air dryer as the average flow rate and temperature of the inlet air decreases in a manner that reduces the energy consumption of the product.
  • Automatically control their output between 20% and 100% in response to changes in the flow rate and/or temperature of the inlet air and/or outlet air.
  • Not exceed the limits set out in the performance criteria below for pressure drop corrected composite specific energy consumption (SEC) at 50%, 75% and 100% load (i.e. rated air flow).
  • Conform with the requirements of The Pressure Equipment (Safety) Regulations 2016 in respect of their design, manufacture and testing procedures, or have an appropriate Conformity Assessment mark.

1.3.2       Performance requirements

Products must not exceed the values for pressure drop corrected composite specific energy consumption (SEC) set out in the Table 1.1 below at the specified percentage of full load.

Table 1.1    Maximum Allowable Composite SEC in kW/m3/min ​​​​​

Percentage of full load (i.e. rated air flow) Maximum allowable Composite SEC (kW/m3/min)
50% <=0.30
75% <=0.40
100% <=0.50

The pressure drop-corrected composite SEC should be calculated as follows:

$$SEC = \frac{P + (1.67 \times \Delta p \times Q)}{Q}$$


P = Total electrical power consumed by air dryer, kW

Δp = Pressure drop across air dryer, bar

Q = Flow rate of air, m3/min

1.4           Measurement and Calculations

1.4.1       Measurement Standards and Test Requirements

All products must be tested in accordance with the procedures and test conditions laid down in BS ISO 7183:2007, which specifies how to measure the electrical power consumed by the product at full load, the pressure drop across the dryer and the flow rate of air through the product. The test results should be presented in the format laid down in Annex B of BS ISO 7183-2:2007.

Products must also meet the Class 4 specifications for moisture removal in BS ISO 8573-1:2010, “Table 2 Compressed air purity classes for humidity and liquid water”

In addition, manufacturers should use the above procedures to evaluate the pressure drop corrected composite SEC of their products at two part load conditions (50% and 75%).

Please note that performance data obtained in accordance with the procedures in ISO 7183: 1986 will be accepted as an alternative to testing in accordance with ISO 7183:2007 until further notice.

1.4.2       Rounding 

For the avoidance of doubt composite SEC data must be presented to 2 decimal places. As an example, a product with a composite SEC of 0.49 at 75% of full load) would be deemed to be a fail.

1.5           Verification for ETL Listing

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-certified
  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing
  • Independent testing

Further information regarding the routes can be found in Guidance Note 5 on the ETL product testing framework[1].

1.6           Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.

[1] ​​​​