HEATING TECHNOLOGY


Efficiency challenges and hybrid solutions


Air source heat pumps require hybrid approaches to balance efficiency, costs and environmental impact in delivering water heating for commercial systems, says Bill Sinclair.


Bill Sinclair www.adveco.co


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Technical director at Adveco


ir source heat pumps (ASHPs) are low-carbon appliances initially designed to work best in lower temperature


systems. Their efficiency is impacted by low ambient temperatures of air, from which heat is being drawn, and the temperature of the water that needs to be input into the domestic hot water (DHW) system. To ensure consistently high output temperatures (+60°C demanded by commercial DHW systems), the heat pump will be required to work harder as the ambient temperature drops, demanding electrical input to the pump. Complex and often very large, commercial heat pumps can be expensive to purchase and operate if they are to deliver heat to a system more effectively than direct electric heating.


Hybrid solutions For DHW, this currently means deploying heat pumps as part of a wider application as opposed to a single technological response to the building’s demands. A ‘hybrid’ approach makes optimal use of the heat pump to deliver lower, sub- 60°C hot water as pre-heat to the system, then topping temperatures up to +65°C using electric boilers or a combination of solar thermal and electric water heating to assure low carbon, cost-effective to operate water heating systems capable of meeting consistent and peak daily demands.


Refrigerant development Maximising the efficiency of heat pumps in commercial-scale building projects is therefore one of the core aims of the HVAC sector, and the development of refrigerants is a key aspect of this work. The more efficient the refrigerant, the greater the potential to deliver consistently higher temperatures from the heat pump for less effort. Higher


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efficiency refrigerants also mean less is potentially required in the unit to achieve the desired heating output, so the heat pump can be more compact and less costly to purchase, install and operate. Increasingly, the prioritisation of refrigerants with low global warming potential (GWP) and zero ozone depletion potential. While R32 is a current popular


refrigerant for DHW, due to its safe and consistent ability to maintain temperatures suitable for system preheat. However, stricter regulations on GWP, which are expected to come into force by the end of this decade in the UK, will impact the use of R32. The industry is therefore turning to the utilisation of natural refrigerants such as carbon dioxide (CO₂) and hydrocarbons (propane), which have negligible or zero GWP. Heat pumps using CO₂ or propane


are already available and claim high output temperatures, in excess of 70°C. To achieve this CO₂-based systems will operate at extremely high pressures, requiring specialised and robust components, which increase the size, costs and complexity of the heat pump. They also best work within narrower windows of ambient temperature. Commercial CO₂ heat pumps also notably struggle when trying to keep the return temperature below 30°C. That is fine if you have continuous high demand, but most commercial systems need to meet peak period demands, and also adapt to little to no demand outside those peaks. It’s these periods where the efficiency of CO₂ heat pumps falls away, and if the return temperature gets too high, the coefficient of performance (COP) drops exponentially, and the unit eventually shuts off because it cannot work any more.


R290, which is propane, offers


greater efficiency than CO₂ and addresses concerns over the GWP. However, the Building Engineering Services Association (BESA) recently voiced concerns over propane as a replacement for high-GWP refrigerants, issuing a warning about the increasing safety risks associated with the use of flammable refrigerant gases in air conditioning and heat pump systems. Given that large commercial ASHPs may be


pre-charged with as much as 50 kg of propane, others have raised concerns over the lack of regulations relating to transportation and storage, where damage is more likely.


Safety considerations For safe installation, propane heat pumps need to be located at a safe distance from each other and other electrical devices. Sparks and electrical discharge are the most likely forms of ignition, so other devices need to be taken into account. Stricter specification of ‘protective zones’ or ‘safety zones’ – far more than 1m – around the units is required. These zones must be free from any building openings (windows, doors, ventilation inlets/outlets) and potential ignition sources. This is especially the case when approaching layouts that incorporate R290 heat pumps and solar PV panels, mounting structures, and associated electrical equipment. This could all drastically limit project design, especially if the intent was to place the units on a rooftop. At Adveco, our recommendation


is to retain R32 ASHPs as a source of preheat to a DHW application, providing greater versatility and assured service for lower investment


Adveco’s FUSION system is an all-electric water heating solution which provides a wide choice of pre-packaged variants


and operational costs. We expect that new, non-flammable refrigerants will replace R32 by the end of the decade. The approach also considerably simplifies installation and demands for space. Primary heat for top up and peak demands can then be supplied with either a gas water heater or electric boiler for greater carbon reduction. The introduction of solar thermal between the ASHP and the primary heat source will further reduce carbon emissions. Solar thermal is up to eight times more effective per m² than PV in cutting carbon emissions from water heating, requires a much smaller, space-saving area, and is intrinsically safe. This hybrid approach, exemplified


by Adveco’s award-winning FUSION system, which combines R32 heat pumps with electric boilers in an indirect system, and adds the option of solar thermal, optimises energy demands and ensures robust provision of daily hot water. It also maximises the use of space for services and lowers upfront and ongoing operational costs, all while meeting sustainability goals. ■


EIBI | SEPTEMBER 2025


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