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Department for Business, Energy and Industrial Strategy

Water to Air Heat Pumps, Multi-split VRF

1.1           Scope

Water to Air Heat Pumps, Multi-Split VRF, are products that are specifically designed to transfer heat from water (in a building’s internal water loop) into the air within the space to be heated by means of a refrigeration cycle.

‘Multi-Split’ type heat pumps have separate heat collection and rejection units for each space known as ‘outdoor’ and ‘indoor’ units. The ‘outdoor’ unit is connected to more than one ‘indoor’ units which are specifically designed to be connected together during installation by refrigerant pipework to form a single functional unit.

Variable refrigerant flow (VRF) heat pumps are specifically designed to automatically adjust the flow of refrigerant to each indoor unit so that the heat delivered is matched to the demand.

1.2           Definitions

Water to Air Heat Pumps, Multi-Split VRF, use an electrically operated refrigeration system to transfer heat from an internal water loop into the air within the space to be heated. They can be used to provide space heating in a wide range of buildings and some products also are able to provide cooling by reversing the refrigeration cycle within the product (these products are known as reversible ‘water cooled’ air conditioning units).

Water to Air Heat Pumps, Multi-Split VRF are available with a range of efficiencies. The Energy Technology List (ETL) Scheme aims to encourage the purchase of higher efficiency products.

The ETL Scheme covers one product category:

  1. Multi-split VRF heat pumps that consist of one ‘outdoor’ unit connected to one or more ‘indoor’ units using a common refrigerant circuit with the indoor units individually controlled.

Systems with cascade refrigerant/other-medium (e.g. water) heat distribution shall be tested using same methodology as other VRF systems, taking into account all additional energy used in supplementary medium loops, such as circulation pumps’ consumption. 

1.3           Requirements

1.3.1       Eligibility requirements

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

To be eligible, products shall:

  • Consist of an ‘outdoor’ unit and one or more ‘indoor’ units that are:
    • Factory–built sub-assemblies.
    • Supplied as a matched set of units.
    • Designed to be connected together during installation.
  • Incorporate an electrically driven refrigeration system that uses a refrigerant which has a Global Warming Potential (GWP) ≤ 750.
  • Be designed for, and include fittings for, permanent installation.
  • Have an appropriate Conformity Assessment mark.

1.3.2       Performance requirements

Eligible products shall meet the performance criteria set out in Table 1.1 below for:

  • Seasonal Space Heating Energy Efficiency for water heat source, as defined by Ecodesign Commission Regulation (EU) 2016/2281
  • Seasonal Space Cooling Energy Efficiency for ground coupled heat sink, as defined by Ecodesign Commission Regulation (EU) 2016/2281

Table 1.1  Performance thresholds for water to air heat pumps,  multi-split VRF


Product Category

Heating mode (ηs,h)

Cooling mode (ηs,c)


Multi-split VRF heat pumps



"≥" means "greater than"

1.3.3    Information requirements

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

  • Whether the model has ‘smart features’. Specifically, this includes the capability to provide information on whether the products are ‘smart ready’ without the replacement or addition of any hardware, which includes the following one or more options:
    1. Demand Side Response Ready
    2. Date Collection Ready, which includes:
      • Storing data on the heat pump or a remote device.
      • The ability to store data for each calendar year as a value per day, per month or per year.
      • The following real time value parameters: electricity energy consumption (kWh); heat delivered (kWh); energy efficiency performance; operating times (days, hrs); number of on/off cycles.
  • The SCOP and SEER for products with an efficiency performance presented in: ηs,h & ηs,c

1.4           Measurement and Calculations

1.4.1       Energy efficiency metrics

Seasonal energy efficiency metrics are used, and should be measured for the ‘Average’ heating season, as defined in Ecodesign Commission Regulation (EU) 2016/2281 and the harmonised standard BS EN 14825:2022:

Seasonal Coefficient Of Performance (SCOP) – overall coefficient of performance of a heat pump using electricity, representative of the heating season, calculated as the reference annual heating demand divided by annual energy consumption for heating (as defined by Ecodesign Commission Regulation (EU) 2016/2281).

Seasonal Energy Efficiency Ratio (SEER) – overall energy efficiency ratio of a heat pump working in reverse mode for a representative cooling season, calculated as the reference annual cooling demand divided by the annual energy consumption for cooling (as defined by Ecodesign Commission Regulation (EU) 2016/2281).

Seasonal Space Heating Efficiency s,h) – ratio between the space heating demand for reference heating season, supplied by a space heater and the annual primary energy consumption required to meet this demand (as defined by Ecodesign Commission Regulation (EU) 2016/2281).

Seasonal Space Cooling Energy Efficiency s,c) – ratio between the space cooling demand for reference cooling season supplied and annual primary energy consumption required to meet that demand.

In case of any changes regarding the value of CC in relevant regulations or test reporting procedures, performance indicators will be calculated using the following equations:

(1)   ηs,h= SCOP/CC -F1

(2)   ηs,c= SEER/CC -F1

The equations for calculating the ηs,h and ηs,c correspond to section 7.2 and section 5.2 of BS EN 14825:2022 respectively.

Primary energy consumption for electricity usage is obtained using Conversion Coefficient (CC), known also as Primary Energy Factor, equal to 2.5, as defined by Ecodesign Commission Regulation (EU) 2016/2281.

Correction factor (F1) is a correction that accounts for a negative contribution to the seasonal space heating energy efficiency of heaters due to adjusted contributions of temperature controls, equal to 3% (BS EN 14825:2022)

Reference heating season, also called climate - set of operating conditions describing per bin the combination of outdoor temperatures and the number of hours these temperatures occur for heating for which the unit is declared fit for purpose There are three reference heating seasons: “A” average, “C” colder and “W” warmer. UK is located in two reference zones: A and W, but for the ETL purposes “A” for average is to be used.

1.4.2       Test Requirements

No additional testing requirements beyond the measurement standard below

1.4.3       Measurement standards

All products shall be tested in accordance with the procedures in Commission Regulation (EU) No 2016/2281 , consistent with BS EN 14825:2022. The conditions for assessing performance are set out in the Table 1.2 below.

Table 1.2    Measurement conditions for water to air heat pumps, multi-split VRF


Product Category

Heating mode (ηs,h)

Cooling mode (ηs,c)


Multi-split VRF heat pumps


Commission Regulation (EU) No 2016/2281 Annex III, tables 21, 26, water rating conditions

Rated capacity (kW): Commission Regulation (EU) No 2016/2281 Annex III, Table 19, water rating conditions 

Commission Regulation (EU) No 2016/2281 Annex III, table 27, ground coupled rating conditions,

Rated capacity (kW): Commission Regulation (EU) No 2016/2281 Annex III, Table 19, ground coupled rating conditions

Please note that performance data obtained in accordance with the procedures and conditions laid down in BS EN 14825:2016 and BS EN 14825:2018 will be accepted as an alternative to testing in accordance with BS EN 14825:2022 until further notice. 

1.4.4       Rounding 

For the avoidance of doubt test data should be presented two decimal places ηs,h and ηs,c values . As an example, a multi-split VRF heat pump with a heating mode ηs,h of 209.4% and cooling mode ηs,c of 224.4% would be deemed to be a fail.

1.5           Verification for ETL Listing

There are five main ways that applicants can demonstrate their product’s performance:

  • 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 a range of products that are variants of the same basic design, test data may be submitted for a representative model, provided that all variants, i.e. models, share following characteristic features:

  • Use the same refrigerant
  • Have the same compressor type (i.e. manufacturer, line of models), which should imply:
    • same method of compression (e.g. reciprocating or scroll) and
    • same type of enclosure (e.g. hermetic or semi-hermetic)
  • Use the same defrosting method (e.g. hot gas defrost)
  • Fit within the same product category (i.e. are all low-temperature air to water heat pumps, or are all non-low-temperature air to water heat pumps.
  • The representative models may be selected by dividing the range of products into groups of models with similar design characteristics. The performance of each model shall be predicted using a validated mathematical model. At least one model in each group shall be tested for validation purposes. A report documenting performed model calculations, showing all significant calculation steps, shall be submitted with the application.

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

The next technical review is scheduled for 2025-26.

1.7.2       Illustrative future direction of the requirements 

Future changes to the Specification may include:

  • Increasing performance thresholds for ηs,h and ηs,c
  • Updating the product eligibility and functionality requirements as per market demand and any UK or EU regulatory changes. 
  • The possibility of ‘smart features’ becoming an eligibility requirement for listed water to air heat pumps, multi-split VRF. 
  • The possibility of updating the product eligibility requirements to encompass the embodied and lifetime carbon of heat pumps. Introducing a maximum value (measured in tonnes/CO2) for the lifetime carbon of a heat pump.