Evaporative Air Coolers :: Energy Technology List

1.1 Scope

Evaporative air coolers can be direct or indirect. With direct evaporative air cooling, outside air is blown through a water-saturated medium and cooled by evaporation. The cooled air is circulated by a fan. With indirect evaporative air cooling, a secondary air stream is cooled by water. The cooled secondary air stream passes through a heat exchanger, where it cools the primary air stream. The cooled primary air stream is circulated by a fan.

Evaporative air coolers are available with a wide variety of efficiencies. The Energy Technology List (ETL) Scheme aims to encourage the purchase of direct evaporative air coolers and higher efficiency indirect evaporative air coolers.

The ETL Scheme covers two categories of product:

Direct evaporative air coolers
Indirect evaporative air coolers

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

1.2 Definitions

An evaporative air cooler is a device that cools air through the evaporation of water.

1.3 Requirements

1.3.1 Eligibility requirements

Direct and Indirect evaporative air coolers shall conform to the following eligibility criteria:

Incorporate one or more electrically powered fans
Incorporate an electrically powered pump to circulate water to a water-saturated medium through which an air stream passes or to spray nozzles in an air stream.
Minimise scale build up with optimised water bleed rates
Maintains conditions compliant with ACoP L8 legionella code of practice and guidance.
Not use air to cool a water stream.
Where products can be programmed to communicate directly with a remote monitoring & control station, across a computer network or a fieldbus, or the internet, they shall demonstrate conformity with the general principles and requirements for cybersecurity set out in:
- The foundational requirements of the IEC 62443 series of standards and all relevant technical security requirements set out in IEC 62443-4-2, or:
- The security baseline requirements of ETSI EN 303 645 for IOT (Internet of Things) enabled products.
Have an appropriate Conformity Assessment mark.

1.3.2 Functionality criteria

Evaporative air coolers shall also conform to specific functional criteria for either direct or indirect evaporative air coolers.

Functional criteria for direct evaporative air coolers

In order for the product to be classified as a direct evaporative air cooler, all of the following criteria shall be met:

The product cools an air stream by moving air through a water-saturated medium which is cooled by evaporation. Moisture must be added to the air stream until it is close to the point of saturation (i.e., the wet bulb depression is close to zero).
The product dry bulb temperature should reduce while the wet bulb temperature remains constant.

Functional criteria for indirect evaporative air coolers

The product will be classified as an indirect evaporative air cooler should any one of the following criteria be met:

The product incorporates a secondary air stream that is cooled by means of evaporation of water. This secondary air stream may be an offshoot from the primary air stream, like in a sub-wet bulb temperature evaporative air cooler, provided that the offshoot secondary air stream is not later recombined to the primary air stream.
The product incorporates a secondary air stream that passes through a heat exchanger in order to provide further cooling to a primary air stream.
The product incorporates a primary airstream with no change in absolute moisture content.

If an indirect evaporative air cooler is specially designed to provide cooling to close control air conditioning equipment, then the product should be listed on the ETL under Close Control Air Conditioning Equipment, and not under Evaporative Air Coolers.

Close control air conditioning equipment covers products that are specifically designed to provide the cooling needed to maintain the air temperature, and optionally the relative humidity, in rooms that contain equipment or processes with high sensible heat loads [1]. These products either incorporate an electrically powered compressor (or compressors) and / or incorporate a chilled water cooling coil with fittings for connection to an external chilled water circuit.

1.3.3 Information requirements

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

1. Air flow (m³/hour)

2. Cooling capacity (kW), defined as:

q=1.21 * Q_p * (t_d1−t_d2)

t_d1 and t_d2 are the primary air inlet and outlet dry-bulb temperatures, respectively
Qp is the primary standard airflow rate (m^₃/s)
1.21 is the factor used by ASHRAE 143 to represent the air density and specific heat of the air

3. Electrical power input (kW), defined as the sum of pump, air-moving device, and any other electric power input due to appurtenances required to produce cooling.

4. Energy Efficiency Ratio (EER), also referred to as the Evaporative System Coefficient of performance (EvaCOP). The EER is the ratio of cooling capacity (kW) to electrical power input (kW).

$$ EER=\frac{Cooling\ capacity\ (kW)}{electrical\ power\ input\ (kW)}$$

5. The evaporative efficiency (or saturation efficiency), (%)

$$Ɛ=\frac{(t_i-t_0)}{(t_i-t_{wi})} x100\%$$

t_i = air inlet dry bulb [°C]
t₀ = air outlet dry bulb [°C]
t_wi = air inlet wet bulb [°C]

6. Water consumption resulting from the water evaporation process (m³/hour).

7. Whether the product can be programmed to communicate directly with a remote monitoring & control station, across a computer network or fieldbus, or the internet, and whether it is IOT (Internet of Things) enabled product.

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

1. Air flow (m³/hour)

2. Cooling capacity (kW), defined as:

q=1.21 * Q_p * (t_d1−t_d2)

t_d1 and t_d2 are the primary air inlet and outlet dry-bulb temperatures, respectively
Q_p is the primary standard airflow rate (m³/s)
1.21 is the factor used by ASHRAE 143 to represent the air density and specific heat of the air

3. Electrical power input (kW), defined as the sum of pump, air-moving device, and any other electric power input due to appurtenances required to produce cooling.

4. Energy Efficiency Ratio (EER), also referred to as the Evaporative System Coefficient of performance (EvaCOP). The EER is the ratio of cooling capacity (kW) to electrical power input (kW).

$$ EER=\frac{Cooling\ capacity\ (kW)}{electrical\ power\ input\ (kW)}$$

5. Cooling Effectiveness (ε), which is the primary air inlet dry-bulb temperature (t_d1) less the primary air outlet dry bulb temperature (t_d2) divided by the primary air entering dry-bulb temperature (t_d1) less the entering secondary air inlet wet-bulb temperature (t_w3).

$$Ɛ=\frac{(t_{d1}-t_{d2})}{(t_{d1}-t_{w3})}$$

6. Water consumption resulting from the water evaporation process (m³/hour).

1.4 Measurement and Calculations

1.4.1 Measurement standards

Values to be tested and reported under the information requirements for Direct Evaporative Air Coolers shall be performed according to:

AS 2913-2000 Evaporative air conditioning equipment; or
ASHRAE 133-2015 ‘Method of testing direct evaporative air coolers’.

All indirect evaporative air coolers shall be tested in accordance with the procedures and test conditions laid down in:

ANSI/ASHRAE Standard 143-2015: Method of Test for Rating Indirect Evaporative Coolers.

Water consumption values for Indirect Evaporative Air Coolers shall be reported as per ASHRAE 133-2015 (section 6.5).

1.4.2 Calculation Requirements

The EER and cooling effectiveness of the evaporative air cooler shall be calculated when operated at an inlet psychometric condition of 35°C dry bulb temperature, and a 24°C wet bulb temperature. Furthermore, the following external resistance (system static pressure) will be applied:

Units up to 4 m³/s = 80 Pa resistance
Units greater than 4 m³/s = 120 Pa resistance

1.4.3 Rounding

For the avoidance of doubt test data should be presented to 1 decimal place.

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-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 a range of two or more products that are variants of the same basic design, test data may be submitted for a representative selection of models, provided that it can be demonstrated that all variants:

Utilise the same core technology as the tested model;
Utilise the same key components as the tested model.

The representative models must be selected by dividing the range of products into groups of models with similar design characteristics, and testing a model in the lowest quartile of predicted performance in each group. The performance of each model in the group must be predicted using a validated mathematical model. As a minimum, at least one model must be tested in each range of products.

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.

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 will consider:

How the 2023 changes to the criteria have encouraged registrations onto the ETL
How the standardisation of performance testing for the technology develops
How the market deployment of the technology unfolds
How evaporative technologies are integrated with other HVAC technologies
Explore the inclusion of direct indirect evaporative air coolers (IDEC).
The reintroduction of a minimum performance requirement for EER or cooling effectiveness.
The adequacy of the cybersecurity criterion for evaporative air coolers.

[1] The close control air conditioning equipment criteria include further details of the eligibility requirements: https://etl.energysecurity.gov.uk/products/heating-ventilation-air-conditioning-hvac/close-control-air-conditioning-equipment

Evaporative Air Coolers