Air to Water Heat Pumps :: Energy Technology List

1.1 Scope

Air to water heat pumps are products that are specifically designed to transfer heat from ambient air outside a building to a water-based heating system, by means of a refrigeration cycle.

This specification covers reversible and irreversible models below 45kW. Products above 45kW may be considered within the Packaged Chillers sub-technology.

1.2 Definitions

An air to water heat pump uses an electrically driven refrigeration system to transfer heat from outside air into a water-based heating system. It is primarily used to provide space heating in a wide range of buildings. Additional functionality which may be available includes:

Provision of heat to domestic hot water
Space cooling using a water loop by reversing the product’s refrigeration cycle.

Air to water heat pumps are available with a wide range of efficiencies and the Energy Technology List (ETL) Scheme aims to encourage the purchase of higher efficiency products.

The ETL Scheme distinguishes between two categories of Air to Water Heat Pumps:

1. Low-temperature heat pumps - specifically designed for low-temperature applications, that cannot deliver heating water with an outlet temperature of 52 °C at an inlet dry (wet) bulb temperature of ‑7°C (‑8°C) in the reference conditions for average climate, with rated output not greater than 45kW.

2. Medium and high temperature heat pumps – that are capable of delivering water with an outlet temperature of 52°C or greater at an inlet dry (wet) bulb temperature of – 7°C (– 8°C) in the reference conditions for average climate, with rated output not greater than 45kW.

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:

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.
Be designed primarily to provide space heating and:
- space heating only, i.e. “space heater” as defined by Commission Regulation (EU) No 813/2013, or
- providing heat to deliver domestic hot water, i.e. “combination heater” as defined by Commission Regulation (EU) No 813/2013.

In addition, single split products shall consist of an ‘outdoor’ unit and an ‘indoor’ unit that are:

Factory–built sub-assemblies.
Supplied as a matched set of units.
Designed to be connected together during installation.

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 (η_s,h), as defined by Commission Regulation (EU) No 813/2013.
Seasonal Energy Efficiency Ratio (SEER) for average climate conditions, where the product is designed to provide cooling.

Table 1.1 Performance thresholds for air to water heat pumps

	Product Category	Heating mode (η_s,h)		Cooling mode (SEER)
		Water at 35 °C	Water at 55 °C
1.	Low temperature heat pumps	≥130%	N/A	≥4.20
2.	Medium and high temperature heat pumps	≥150%	≥130%	≥4.30

"≥" means "greater than or equal to"

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 for products with an efficiency performance presented in: η_s,h
The η_s,c for products with an efficiency performance presented in: SEER.

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) 813/2013 and the harmonised standard BS EN 14825:2018:

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.

Seasonal Energy Efficiency Ratio (SEER) – ratio of the total cooling capacity to the effective power input of the unit.

Seasonal Space Heating Energy Efficiency (η_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.

The equation for calculating η_s,h corresponds to section 8.2 of BS EN 14825:2018:

(1) η_s,h= SCOP/CC -F1

Seasonal Space Cooling Energy Efficiency (η_s,c) – ratio between the space cooling demand for reference cooling season supplied and annual primary energy consumption required to meet that demand, as defined BS EN 14825:2018.

The equation for calculating η_s,c corresponds to section 5.2 of BS EN 14825:2018:

(2) η_s,c= SEER/CC -F1

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) 813/2013.

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 14825:2018).

Reference heating season, also called climate – a 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

Performance data shall be determined and the η_s,h calculated, following the requirements of Commission Regulation (EU) No 813/2013 and harmonised standard BS EN 14825:2018 “Air conditioners, liquid chilling packages and heat pumps, with electrically driven compressors, for space heating and cooling - Testing and rating at part load conditions and calculation of seasonal performance.”, and the specific requirements of Table 1.2 below.

Table 1.2 Measurement conditions for air to water heat pumps

Product category

Heating mode

Cooling mode

Low temperature heat pumps

Commission Regulation (EU) No 813/2013, Annex III, Tables 4 and 5 and Table 3 for outdoor air and low-temperature heat pumps

Rated capacity (kW): Commission regulation (EU) No 813/2013, Annex III, Table 3.

BS EN 14825:2018
Table 4, At Average Climatic Conditions, cooling floor application

Rated capacity (kW): BS EN 14825:2018, Table 11, cooling floor application

Medium and high temperature heat pumps

Commission Regulation (EU) No 813/2013, Annex III Tables 4 and 5 and Table 3 for outdoor air and heat pump space heaters other than low-temperature heat pumps

Rated capacity (kW): Commission regulation (EU) No 813/2013, Annex III, Table 3.

BS EN 14825:2018
Table 4, At Average Climatic Conditions, cooling floor application

Rated capacity (kW): BS EN 14825:2018, Table 11, cooling floor application

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

The η_s,h shall be calculated in accordance with the requirements of Commission regulation (EU) No 813/2013 Annex III, by dividing the SCOP by the factor 2.5 (to allow for generation efficiency), corrected by contributions accounting for temperature controls.

Where results are determined by calculation then this should be on the basis of design and/or extrapolation. In this case, details of such calculations and/or extrapolations, and of tests to verify the accuracy of the calculations undertaken (including details of the mathematical model for calculating performance of such combinations, and of measurements taken to verify this model) shall be made available.

1.4.4 Rounding

For the avoidance of doubt test data should be presented to zero decimal places for percentage points in η_s,h values and to two decimal places for SEER indicators. As an example, a low temperature heat pump with a cooling mode SEER of 4.194 or a heating mode η_s,h of 129.4% 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 η_s,h and/or SEER,
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 air to water heat pumps.
The possibility of updating the product eligibility requirements to encompass embodied lifetime carbon of heat pumps. Introducing a maximum value (measured in tonnes/ CO₂) for the lifetime carbon of a heat pump.

Air to Water Heat Pumps