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  4. Air Blast Coolers

Air Blast Coolers

1.1    Scope

Air blast coolers (including ‘ambient air pre-coolers’ and ‘dry adiabatic coolers’, and commonly known as ‘free coolers’ and ‘hybrid coolers’, and previously referred to as ‘forced air pre-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 make use of adiabatic cooling for limited periods.

Air blast coolers can be used to reduce the load on refrigeration systems by cooling water and other process liquids, prior to their transfer into the refrigeration system.

Air blast coolers can be broadly categorised as packaged air blast free coolers and general air blast coolers. Packaged air blast free 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 free 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.

The Energy Technology List (ETL) Scheme encourages the purchase of free standing air blast coolers that either turn off the cooling fan when the ambient air temperature is high, and/or feature variable speed fan(s) with appropriate controller to modulate the cooling fan speed according to cooling demand.

Air blast coolers that are sold as an integrated part of a mechanical chiller are not included in this category, but are covered by the ‘Packaged Chillers’ sub-technology of the ETL.
To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

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), prior to transfer to a refrigeration system. 

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.
  • 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.

In addition air blast coolers shall incorporate:

Either:

  • 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.

And/Or:

  • a variable speed fan(s) with appropriate controller which reduces the duty of the cooling fan as the cooling demand decreases, or as the ambient air temperature decreases 

1.3.2    Performance requirements 

Eligible 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 (>=) 100.0.

All packaged air blast free coolers are eligible, and do not need to meet a minimum EER performance threshold.  

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 99.9 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 four routes can be found in Guidance Note 5 on the ETL product 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, 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 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.  

1.6    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.