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Department for Business, Energy and Industrial Strategy

Desiccant Air Dryers with Energy Saving Controls

1.1           Scope

Desiccant air dryers are commonly fitted to compressed air systems to prevent moisture from condensing within pipe work and equipment. They are typically utilised where compressed air is needed at higher quality or with a lower dew point than can be achieved by a refrigerated air dryer.

They contain a desiccant material which absorbs the moisture and is then regenerated, for example, by blowing air through the dryer.

The direct energy usage of a desiccant air dryer typically increases the energy used in compressed air generation by between 10% and 25% depending on the product design and how it is controlled. Indirect energy usage, in the form of the pressure drop across the dryer and the compressed air used for purging can increase the overall energy usage in compressed air generation by between 20% and 50%. 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. The aim of the ETL Scheme is to encourage the purchase of models which use energy efficient methods of desiccant regeneration, have low pressure drops across them and include energy savings controls.

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

1.2           Definitions

Desiccant air dryers are products that are specifically designed to extract water vapour from industrial compressed air systems by absorbing moisture using a desiccant material which is then, for example, regenerated by blowing air through the dryer.

1.3           Requirements

1.3.1       Eligibility requirements 

To be eligible, products must:

  • Have a dew point rating of -40ºC i.e. Class 2 specifications for moisture removal in BS ISO 8573-1:2010.
  • Utilise a regeneration method which is either heatless or internally/externally electrically heated or utilises a blower or vacuum system. Desiccant dryers that utilise steam, heat of compression or are heated in any way other than electrically are not eligible.
  • Incorporate dew point sensing controls that automatically control the regeneration cycle to optimise the time between regenerations depending on the dew point of the exit air in a manner that reduces the energy consumption of the product.
  • Not exceed the limits set out in the performance criteria below for the composite specific energy consumption (SEC) at 100% load (i.e. rated air flow), corrected for the pressure drop across the dryer and any compressed air used by the dryer for regeneration, purging and/or cooling.
  • 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 composite specific energy consumption (SEC), corrected for the pressure drop across the dryer and any compressed air used by the dryer, set out in the Table 1.1 below at 100% load (i.e. rated air flow).

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)

100%

<= 1.07

The composite SEC should be calculated as follows:

$$SEC = \frac{P + (1.67 \times \Delta p \times Q) + (5 \times C)}{Q - C}$$

Where:

P =   Total electrical power consumed by air dryer, inclusive of any

         external heaters, blowers, vacuum pumps or other associated

              equipment, kW

Δp = Pressure drop across air dryer, bar

Q =   Flow rate of air, m3/min

C =   Total compressed air loss of air dryer for regeneration, purging, cooling

         or any other purpose, 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, compressed air loss 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 2 specifications for moisture removal in BS ISO 8573-1:2010, “Table 2 Compressed air purity classes for humidity and liquid water”

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 1.08 at 100% 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] https://www.gov.uk/government/publications/energy-technology-list-etl-product-testing-framework