Heat Pump Association HRSC0056
Heat Pump Association response to the inquiry: Heat resilience and sustainable cooling
The HPA is the UK’s leading authority on the use and benefits of heat pump technology and includes the country’s leading manufacturers of heat pumps, components, and associated equipment as well as energy companies, certification bodies, installers and training providers. Proposals put forward by the HPA are developed closely with a membership base that represents around 96% of the heat pump market manufacturing share, including all of the large multinational companies providing products to the UK market, ensuring that the proposals are workable and credible.
The Association works to support policymakers in the development of effective heat decarbonisation policy and other matters that affect the interests of end users, wider stakeholders, and the industry.
The HPA recognises that heat pumps will only fulfil their promise in the market if suppliers, installers, and users fully appreciate their function and capabilities and we work hard to provide impartial, factual guidance and supporting materials to enable this.
HPA Response
The HPA would like to submit the following information in response to the following specific question:
“What role might reversible heat pumps (which can act as both heating and cooling systems) and other emerging technological solutions, such as the development of smart materials, play in meeting future cooling demands?”
Most fixed air conditioning units today are reversible Air-Air Heat pumps (AAHP), that provide both heating and cooling. In residential applications, the most common type is multi-splits, where one outdoor unit is connected to one or more indoor units via refrigerant pipework. The indoor unit then heats or cools the indoor air. The most common indoor units are mounted high on the wall at ceiling height. AAHP can provide a useful solution in existing properties that suffer overheating issues, as it provides both heating during the cold season and air cooling during the peak summer days.
Currently, in the UK, the highest proportion of residential heat pumps for heating purposes are hydronic heat pumps, either Air-Water heat pumps (AWHP) or Ground Source heat pumps (GSHP). The heat pump warms water that then circulates in the radiator system and to the hot water cylinder.
Air conditioning for buildings has until recently been primarily for commercial buildings, not for residential buildings, where only 3-5% of homes are estimated to have some form of cooling device between 2013-2019[1]. During the COVID pandemic, while more people were working from home, many air conditioning installers reported an increase in enquiries for residential applications, e.g. for extensions, garden rooms, conversions, etc. People required heating/cooling solutions for their workspace and sought an efficient heating solution that was easy to retrofit into their adapted workspace, plus summertime cooling. For these reasons, anecdotally, more air conditioning installers report they now also offer installations for domestic applications.
AAHPs offer a more efficient alternative to a direct electric heating device and the flexibility of comfort cooling during peak summer temperatures. Energy ratings are displayed on the Energy Label of the products to show the seasonal efficiency ratings for heating (SCOP) and cooling (SEER), and also annual energy consumption and noise levels. These values vary depending on the combination of indoor and outdoor units. As an indication of the level of performance, for multi-split AAHP, the Energy Technology List requires a minimum SEER above 6.6 and minimum SCOP of 4.3[2]. They are typically selected instead of extending an existing hydronic (gas) heating system. If hot water is also required in conjunction with the AAHP installation, several separate and unconnected DHW systems may be offered: (i) a direct electric hot water tank, (ii) a point of use water heater, (iii) a domestic hot water heat pump (DHW-HP). One novel system that has not gained much interest in the UK so far uses a refrigerant coil wrapped around the outside of a hot water cylinder.
The most common type of residential heat pump is a hydronic Air-Water Heat Pump (AWHP). Some models are reversible but tend to be slightly more expensive. Reversible models have historically been omitted from incentive schemes and therefore have limited take-up. Reversible AWHP are typically coupled with hydronic fan coil units sited indoors, sometimes known as heat pump convectors. With careful design, AWHP may be combined with a correctly dimensioned and adequately controlled Underfloor heating (UFH) pipework system to offer a limited cooling capacity, as long as controls are in place to prevent condensation formation on the floor. AWHP are not compatible with traditional wet radiators due to condensate formation on the radiator surface. Ground Source Heat Pumps (GSHP) can also provide this type of ‘active cooling’ and have the benefit that even those that aren’t reversible at the time of manufacturer/installation can relatively easily be modified to do so.
All GSHP models can be equipped with optional passive cooling. Using a separate module consisting of a plate heat exchanger and diverter valve, the water in the distribution system bypasses the GSHP and utilises the cooler temperature of the ground to deliver a degree of ‘free’ or “passive cooling”. Again, low temperature water is distributed via hydronic fan coils, passive beams or other similar “wet” systems.
In GSHP passive cooling systems, particularly those installed on a vertical boreholes system, the heat removed from the building is used to recharge the ground array and improve the overall efficiency of the system, rather than just throwing it away. This is simply achieved by passing the fluid of the cooling system through a plate heat exchanger with the ground array fluid passing through the other side and returning to the ground array where the heat is transferred. This heats the ground array improving the system’s efficiency to provide hot water at any time of year and to provide heating in the winter. This saves money in the running of the system and could reduce capital costs in the case of heat pump installations with vertical boreholes. If the heat provided by cooling the home can be accurately quantified, a smaller amount of the ground has a greater heating capacity which reduces the drilling depth of installation.
Networked heat pumps may connect a mix of buildings, such as dwellings and commercial blocks, to combine the heating and cooling demands thereby offering the opportunity for efficiency improvements and reduced capital equipment. Networked GSHPs also offered reduced ground array infrastructure costs, and balanced loads means borehole depths can usually be reduced.
Dedicated active cooling heat pumps, which have a much higher running cost than passive cooling systems, can be deployed where higher cooling loads are required, such as for glazed offices or server rooms. These can be connected to the same ambient temperature loops to recycle waste heat, recharge the ground array and improve the overall system efficiency.
Novel cooling technologies already exist utilising smart materials such as Phase Change Materials, which are designed to help reduce the operating hours of the mechanical cooling system. These tend to be focused on commercial cooling applications and have had limited take-up. In Scandinavia where the proportion of homes with residential heat pumps is high, the most common type is AAHP[3].
There are some differences in the application of incentives and treatment of AAHP compared to hydronic heat pumps.
To be recognised in a residential EPC, all novel products have to be covered by a suitable SAP Appendix Q method. It takes considerable time (3-5 years) for the BRE to develop a new SAP-Q assessment method, which is funded entirely by the interested manufacturers/parties. At the start of the process, there is no indication of the likely level of success or possible benefit in SAP for the novel technology, and this means a high level of risk for innovative manufacturers.
Currently, it is also difficult to get passive cooling systems recognised in Building Regulations Part O (overheating mitigation requirements). This is because it is hard to quantify the cooling offered by the passive cooling system in accordance with the CIBSE cooling load calculation due to the influence of the ground on the cooling availability.
These barriers may stifle innovation and development of new novel residential cooling solutions.
August 2023
[1] https://www.gov.uk/government/publications/cooling-in-the-uk
[2] https://etl.beis.gov.uk/products/heat-pumps/air-air-heat-pumps-split-multi-split-and-vrf