How to select a heat pump with the right type of refrigerant

For those of us working to future-proof heating and hot water systems, the heat pump has become central to the journey towards low-carbon buildings. Although the benefits of heat pumps are undeniable, the efficiency of heat pump systems relies on an unsung hero: the refrigerant.

It’s not as simple as selecting a heat pump anymore – it’s about choosing the right refrigerant for the right application. This is especially critical for plumbing and heating professionals aiming to deliver sustainable, regulation-compliant solutions.

Role of the refrigerant

At its core, a heat pump transfers heat from one place to another using a refrigerant cycle. It’s the refrigerant that absorbs heat from the source (air, water or ground) and releases it into the heating system. So, the performance, environmental impact and even the cost of running the system can hinge on which refrigerant is chosen.

Historically, refrigerants such as CFCs and HCFCs were widely used, but their high Ozone Depletion Potential (ODP) and Global Warming Potential (GWP) will lead to their future phase-out. This leaves us with two main categories:

• Natural refrigerants: such as R290 (propane) and R744 (carbon dioxide)
• Synthetic refrigerants: such as R32 (difluoromethane).

Each has advantages and drawbacks, which must be understood in context.

Understanding GWP and legislation

GWP is the benchmark for assessing a refrigerant’s climate impact, comparing it to CO₂ over 100 years. The lower the GWP, the lower the contribution to climate change. The 2014 F-Gas Regulations – and, more recently, the EU’s Regulation 2024/573 – are pushing for a refrigerant phasedown, promoting the use of low-GWP alternatives.

Compliance with these regulations isn’t optional. Even though some commitments, such as TM44 assessments, remain underused or misunderstood, they should be considered best practice.

Synthetic option: R32

R32 is a popular choice for commercial air source heat pumps. With a GWP of 675, it’s significantly lower than its predecessors. One of the common misconceptions is that R32 can’t produce high enough temperatures for UK heating demands. That’s simply not true. Most R32 systems can reliably produce flow temperatures up to 55°C, making them ideal for space heating, provided the system is well designed.

Designing for R32 requires a narrow differential temperature (DT) approach and careful control of return water temperatures. But when these parameters are met, the result is a highly efficient and cost-effective system.

Natural alternatives: R290 and R744

Natural refrigerants are attracting more attention, and for good reason. R290 and R744 boast ultra-low GWP values – just three for R290 and one for R744. This makes them highly attractive from a sustainability standpoint.

R290 can deliver temperatures up to 75°C, making it a strong candidate for domestic hot water production and high-demand commercial systems. However, safety considerations and risk assessments must be built into the design and installation process due to its flammability.

R744 heat pumps are especially efficient when operating in a 65-70°C flow / 30°C return temperature range. They’re capable of accepting slightly higher return temperatures (up to 50°C temporarily), making them adaptable to more varied applications. However, CO2 systems require precise design due to their high operating pressures and unique transcritical cycle.

Performance metrics: COP and SCOP

Two key indicators of heat pump performance are the Coefficient of Performance (COP) and its seasonal variant, SCOP. COP is the ratio of heat output to electrical input at a specific condition, while SCOP accounts for temperature variations over a year.

Natural refrigerants such as R744 or R290 can show high SCOP values in suitable applications, particularly domestic hot water systems. However, achieving optimal SCOP means marrying refrigerant choice with building design, control strategy and realistic expectations around flow temperatures.

Designing for efficiency

No matter the refrigerant, successful heat pump design demands an integrated approach. This can include:

• understanding the heating demand profile
• designing with a lower flow temperature
• implementing variable flow control strategies
• educating clients about realistic operating conditions.

Contrary to popular belief, a heat pump doesn’t need to match the flow temperature of a gas boiler, if correctly designed. Instead, the system should be optimised around what a heat pump can efficiently do. High-temperature outputs are possible, but not always necessary.

Cost, compliance and the future

While refrigerant type can influence system cost, natural options such as R290 and R744 are becoming increasingly viable as technology improves and demand grows. Still, system cost isn’t just about the unit – it includes installation, building fabric upgrades, maintenance, training and compliance with safety standards.

As installers, engineers and consultants, we all have a role in supporting the UK’s decarbonisation goals. Understanding refrigerants isn’t just a technical necessity – it’s a professional responsibility. Whether you’re specifying a new commercial plant room or retrofitting an older building, your choice of refrigerant can increase the system’s performance, decrease the environmental impact and improve the long-term viability.

With evolving regulations and growing emphasis on whole-system efficiency, now is the time to brush up on refrigerant knowledge and explore the full potential of heat pumps in commercial settings.

• For more information, visit: idealcommercialboilers.com