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Department for Business, Energy and Industrial Strategy

Active Chilled Beams

1.1   Scope

Active chilled beams incorporate an integral (primary) air supply and cooling coil(s) to provide cooled air into occupied spaces without the use of an integral fan, in order to achieve comfortable working conditions. The primary air supply enhances and controls the induction of air from the occupied space through the cooling coil.

Active chilled beams may provide space cooling only or both space heating and cooling. Where beams provide space heating, they will also incorporate a heating coil to provide warm air to occupied spaces.

1.2   Definitions

Active chilled beams are terminal units attached to heating, ventilation and air conditioning (HVAC) systems that are specifically designed to provide chilled air (and warm air for heating and cooling products) into a treated environment.

Cooling only active chilled beams are convectors with an integrated (primary) air supply and cooling coil(s) through which chilled water passes to provide the cooling effect. Heating and cooling active chilled beams also have an integrated heating coil to provide space heating. Primary ventilation air produces an inductive effect to increase the convection of room air. The induced air flow passes through the cooling or heating coil, and then mixes with the primary air before being discharged into the space through integral air distributors.

Active chilled beams do not incorporate fans for air distribution. They are designed to use dry (sensible) cooling to prevent condensation thus negating the need for condensate collection and disposal. Dehumidification of the primary supply air is important to prevent the risk of condensation as well as any internal latent gains.

Active chilled beams can be linear or modular in format:

  • Linear active chilled beams are produced in various widths and lengths with either one or two directional air throw patterns (1 or 2-way throws). One or more linear active chilled beams can be installed as a continuous linear beam to make up desired length.
  • Modular or cassette format active chilled beams are characterized by modular sized units, typically 0.6m x 0.6m and 0.6m x 1.2m with 4 directional outlets (4-way throws).
  • Multi-service chilled beams (MSCBs) combine chilled beams with additional building services such as lighting, controls & control sensors, sprinklers, cables or public-address speakers.

The Energy Technology List (ETL) scheme aims to encourage the purchase of active chilled beams which are energy efficient due to their use of relatively high chilled water temperatures and the use of outdoor ventilation air, resulting in increased efficiency of chiller operation and the opportunity to maximise free-cooling.

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:

  • Be an active chilled beam designed to introduce primary ventilation air into the treated space through the beam.
  • Be designed to operate above the dew point. Any condensate tray fitted should be included as a precautionary measure only, and should have no facility to connect to drainage.
  • Not include any electrical heating elements.
  • Not include an integral fan

Multi-service chilled beams that contain lighting equipment are eligible as long as the lighting equipment also meets the relevant ETL criteria for high efficiency lighting units, white light emitting diode lighting units, or lighting controls, as appropriate.

1.3.2      Performance requirements

Products shall have a “Specific Waterside Cooling Capacity” that is greater than or equal to the values set out in Table 1.1 for “Linear Active Chilled Beams” and Table 1.2 for “Modular Active Chilled Beams” and Table 1.3 for “Bulkhead Active Chilled Beams” at the operating conditions specified below.

Table 1.1    Linear active chilled beam performance requirements

Nominal Active  Chilled Beam Width ≤ 300mm > 300mm and ≤ 600mm
Air Throw 1-Way 2-Way 1-Way 2-Way
Induction (nozzle) pressure (PA) ≤ 100 Pa ≤ 100 Pa ≤ 100 Pa ≤ 100 Pa
Cooling coil pressure drop (PW) ≤ 20 kPa ≤ 20 kPa ≤ 20 kPa ≤ 20 kPa
Specific waterside cooling capacity ≥ 15.0 W/mK ≥ 25.0 W/mK ≥ 20.0 W/mK ≥ 45.0 W/mK

Table 1.2    Modular active chilled beam performance requirements

Nominal Active Chilled Beam Size
(Active width x Active length)
600mm x 600mm 600mm x 1200mm
Air Throw 4-Way 4-Way
Induction (nozzle) pressure (PA) ≤ 100 Pa ≤ 100 Pa  
Cooling coil pressure drop (PW) ≤ 20 kPa ≤ 20 kPa  
Specific waterside cooling capacity ≥ 45.0 W/mK ≥ 40.0 W/mK  

Table 1.3    Bulkhead active chilled beam performance requirements

Nominal Active Chilled Beam Size
(Active length)
Bulkhead unit up to 1500mm
Induction (nozzle) pressure (PA) ≤ 100 Pa
Cooling coil pressure drop (PW) ≤ 20 kPa
Specific waterside cooling capacity ≥ 40.0 W/mK


  • Specific waterside cooling capacity in W/mK is the waterside cooling capacity per unit length of beam and per unit temperature difference between the reference room air temperature and the mean chilled water temperature. For modular active chilled beams, the specific waterside cooling capacity is measured for the modular unit in W/K.
  • Nominal active chilled beam width/dimensions is the size of the active cooling element excluding architectural components that do not affect product cooling performance
  • All other terms are as defined in BS EN 15116:2008
  • “≤” means “less than or equal to”, “≥” means “greater than or equal to”

1.4   Measurement and Calculations

1.4.1      Measurement standards

Product performance specified in Table 1.1, Table 1.2 and Table 1.3 (above) shall be determined in accordance with the procedures and test conditions laid out in the following standard:

  • BS EN 15116:2008 “Ventilation in buildings. Chilled beams. Testing and rating of active chilled beams”

1.4.2      Performance metric

The specific waterside cooling capacity for the product shall be calculated using the equation below:

$$ Specific\ Waterside\ Cooling\ Capacity=\frac{P_W}{LΔθ}$$


  • Pw =            Waterside cooling capacity [Watts]
  • L   =            Cooling length [metres], the active length of cooling section
  • Δθ  =          Temperature difference between reference air temperature (θr) and mean cooling water temperature (θw) i.e. Δθ = (θr – θw) [Kelvin]

For modular active chilled beams, where the product is a fixed size, the specific waterside cooling capacity is simply the ratio between the waterside cooling capacity in Watts to the temperature difference between reference air temperature and mean cooling water temperature in Kelvin, as described above.

1.4.3      Test Requirements

All products shall be tested in accordance with the procedure set out in BS EN 15116:2008. A test report shall be submitted in accordance with the format specified in Section 6 of BS EN 15116:2008.

1.4.4      Rounding 

For the avoidance of doubt test data should be presented to one decimal place. As an example, a Specific Waterside Cooling Capacity of 14.9 Watts/mK for a 1 Way throw linear active chilled beam with Nominal Active Width of ≤ 300 mm would be deemed to not meet the performance requirements. 

1.4.5      Uncertainties of measurement

The total calculated uncertainty when calculating the specific waterside cooling capacity of a product shall be less than ±6% at nominal flow and Δθ = 8K, in accordance with Section 5 of BS EN 15116:2008.

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 have:

  • the same cooling coil width
  • the same cooling coil height
  • fins that are made from the same material, with the same surface and spacing between adjacent fins
  • pipes that are the same shape (e.g. internally smooth or rifled), and of the same material and pattern.
  • the same plenum and diffuser geometry
  • the same discharge (e.g. are all one way, two ways, three ways or four ways)

As a minimum, at least one representative model shall be tested in each range of products. The performance of each model in the representative group shall be predicted using a validated mathematical model.

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 for review during the 2022/23 ETL review cycle.

1.7.2      Illustrative future direction of the requirements 

In future, the ETL technology specification for active chilled beams sub-categories will be reviewed for a potential scope expansion to include other product types not currently covered under the scope of this specification.