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Air Blast Coolers

1.1    Scope

Air blast coolers normally consist of a finned tube heat exchanger and a cooling fan(s). The cooling fan is used to force air over the heat exchanger and to cool water and other process liquids as they passed through the heat exchanger.  Some products also circulate water in the path of the forced air when the outside air temperature is high (known as adiabatic cooling).

Air Blast Coolers are referred to in industry using several different terms, such as ‘ambient air pre-coolers’, ‘dry adiabatic coolers’, ‘hybrid coolers’, ‘forced air pre-coolers’ and ‘free coolers’.

Within the Energy Technology List (ETL), two categories of Air Blast Cooler are defined:

  • Dry Coolers
  • Adiabatic Coolers

The two main applications for Air Blast Coolers are to (a) reduce the load on refrigeration systems by cooling water and other process liquids, prior to their transfer into the refrigeration system or (b) to provide cooling of water and other process liquids without a refrigeration system, where the required output temperature of the fluid is above the ambient air temperatures.

The ETL makes a distinction between General Air Blast Coolers, and Packaged Air Blast Coolers:

  • Packaged Air Blast Coolers include the valves and control systems required for use as a pre-cooler to a refrigeration chiller with full, partial or no free cooling depending on the ambient conditions. The Packaged Air Blast Cooler is bypassed when ambient conditions are not suitable for free cooling.
  • General air blast coolers (also known as dry coolers) are sold ready to connect to any suitable closed circuit cooling system.

Air blast coolers that are sold as an integrated part of a mechanical chiller are not included in the scope of these criteria, but are covered by the ‘Packaged Chillers’ sub-technology of the ETL.

1.2    Definitions

Air Blast Coolers are products that are specifically designed to cool water or process liquid by means of a heat exchanger, over which air is forced by a fan(s).

Dry Coolers are a self-contained system, that cools a single phase liquid by rejecting sensible heat via a heat exchanger to air that is mechanically circulated by integral fan(s)

Adiabatic Coolers are Dry Coolers, with the additional functionality of presenting liquid water into the path of the air in order to reduce the air temperature through evaporative cooling before it reaches the heat exchanger, allowing continued operation at times of higher ambient air temperatures. 

Packaged Air Blast Coolers include the valves and control systems required for use as a pre-cooler to a refrigeration chiller with full, partial or no free cooling depending on the ambient conditions. The Packaged Air Blast Cooler is bypassed when ambient conditions are not suitable for free cooling.

Energy Efficiency Ratio (EER) is the ratio between the net cooling duty of the Air Blast Cooler and the effective energy input to provide the cooling duty.

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

1.3    Requirements 

1.3.1    Eligibility requirements  

To be eligible, products shall:

  • Incorporate a heat exchanger designed to cool water or other process liquids.
  • Incorporate a fan(s) which forces air over the heat exchanger.
  • Incorporate one or both of the following:
    -    A series of control valves (or “by-pass mechanism”) that re-direct the water or other process liquid around the pre-cooler in response to a control signal, and a controller that operates the by-pass mechanism and turns off the cooling fan at times when the ambient air temperature is higher than the water/process liquid inlet temperature. 
    -    Use variable speed fan(s) with an appropriate controller which reduces the duty of the cooling fan as the cooling demand decreases, or as the ambient air temperature decreases.
  • Fans shall be compliant with Ecodesign Regulation (EU) No 327/2011
  • Conform with the requirements of The Pressure Equipment (Safety) Regulations 2016 in respect of its design, manufacture and testing procedures, or have an appropriate Conformity Assessment mark.

1.3.2    Performance requirements 

Dry Coolers & Adiabatic coolers that are not part of a package (i.e General Air Blast Coolers) shall have:

  • A minimum energy efficiency rating (EER) that, at a 5K liquid temperature difference (i.e., difference between inlet and outlet liquid temperatures) and a 15K approach temperature difference (i.e. difference between inlet air and outlet leaving water temperature) and when operating at maximum cooling capacity (as stated on the datasheet), is greater than or equal to (>=) 90.0.

Dry Coolers & Adiabatic Coolers that are part of a package (i.e. Packaged Air Blast Coolers) do not need to meet a minimum EER performance threshold.

1.3.3    Information Requirements

Suppliers shall report the following parameters for each model, which will be published on the ETL Product Search:

  • Air Blast Cooler Packaged or General (Packaged or General)
  • Air Blast Cooler Profile (Flat, Vertical, Vee or Other)

1.4    Measurement and Calculations

1.4.1    Performance metrics

Where EER = net cooling capacity (kW) / effective power input (kW).

1.4.2    Measurement Standards and Test Requirements

The required minimum performance shall be demonstrated using Method A or B, as set out in 1.4.2.1 and 1.4.2.2 below.

For both methods A and B, the liquid for the test shall be water. Effective measured power input is the electricity required to run the fan(s) at full speed plus any control equipment. Water pump power shall not be included. The measurement of air flow will not be required as part of the test. Hybrid coolers shall be run dry i.e. without adiabatic cooling.  

1.4.2.1    Method A - Direct Measurement

Product performance shall be demonstrated by measuring the cooling capacity and power input in accordance with the test procedure in BS EN 1048:2014 at a 5K liquid temperature difference and at 3 test points corresponding to a 10K, 15K and 20K difference in approach temperature. The EER should be determined for each test point. The approach temperature is the difference in temperature between the outlet water leaving the product and the inlet air temperature onto the product (i.e. the ambient temperature condition of the inlet air).

1.4.2.2    Method B - Indirect Measurement

Product performance shall be demonstrated by two separate tests conducted on the same product model and in accordance with BS EN 1048:2014, using a different set of operating conditions for each test. The product performance and EER at a 5K liquid temperature difference and 15K inlet temperature difference shall then be determined by extrapolation from the test results.

1.4.3    Rounding  

For the avoidance of doubt test data should be presented to 1 decimal place. As an example, an EER of 89.9 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
  • Representative testing (see clause 1.5.1)

Further information regarding the first three routes can be found in the ETL Testing Framework.

1.5.1    Representative testing

Where applications are being made for two or more products that are variants of the same basic design, heat exchanger test data or predictions using a validated mathematical model may be submitted for a single representative model.

Data from proprietary Air Blast Cooler sizing software (e.g. of the type used by the manufacturer for sales purposes) may be submitted as evidence for the performance of other models based on the variant, provided the manufacturer submits supporting information regarding the sizing software, to allow the ETL administrator to determine its suitability and effectiveness, including which variants/models have data from testing.

Representative testing can be followed provided that all variants:

  • Use air to liquid heat exchangers of the same constructional design.
  • Have the same general arrangement of fans and heat exchangers.
  • Are constructed from materials with same heat transfer characteristics.
  • Have the same (+/- 5%) or better energy efficiency as the representative models.

Since model numbers are dependent on configuration, dimensions, number and type of fans, heat exchanger coil number and fin type, wild cards designated by ‘*’ symbol can be used for representative models as long as the criteria listed above are met. For example, LF-PA2**T2*-080N06D, where the wild card is applied to number of fans per row, and orientation (horizontal or vertical). 

Evidence supporting representative models, including a description of the fan and heat exchanger configuration, fan area to coil area ratios, dimensions and orientation shall be provided (e.g., technical brochure).

It should be noted that:

  • If a manufacturer voluntarily removes the representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL.
  • If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative model will be removed from the ETL.

1.5.2    Model Ranges

It is recognised that the number of variants for a single model of Air Blast Cooler is often very high, due to the modular nature of the product. The ETL therefore allows for ‘model range’ testing and verification, to reduce the burden on manufacturers.

The model range listing will state the model codes of the products that are covered by the listing, and the range of efficiencies that are covered by the listing – but the individual products themselves are not registered.

A model range may be registered by providing:

  • Evidence of the performance of products within the range. The representative testing approach presented in Section 1.5.1 may be used for this purpose, including the use of proprietary sizing software. In the case of model ranges, the requirement that all variants have the same or better efficiency does not apply.
  • A list of all model codes that are proposed to be covered by the listing, as well as a key describing how to interpret the code. This should be sufficient to confirm that the eligibility criteria of the products have been met.

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.

1.7    Review 

1.7.1    Indicative review date 

This specification is scheduled to be reviewed during the 2025/26 review cycle.

1.7.2    Illustrative future direction of the requirements  

The next technical review of these criteria will consider:

  • Having separate EER requirements for each of the two product-categories (Dry Coolers, Adiabatic Coolers).
  • Including the need to report sound performance of the Air Blast Cooler using the standards stated below, with fans at full speed, namely:
    • Sound Power, LW, measured in accordance with BS EN ISO 9614-1:2009
    • Sound Pressure at 10 metres, LP, measured in accordance with BS EN 13487:2019 standards.