Refrigerant

What is a refrigerant and how does the vapour-compression cycle work?

A refrigerant is the working fluid circulating in heat pumps and air conditioners. It continuously changes state between liquid and vapour, absorbing heat from one location and rejecting it elsewhere through a four-stage cycle called the vapour-compression cycle.

In the evaporator, the refrigerant evaporates while absorbing heat. This is where the system draws energy: in heating mode, heat comes from outdoor air or the ground; in cooling mode, it comes from indoor spaces. The resulting vapour flows to the compressor, which raises its pressure and temperature using mechanical work. The hot, pressurised vapour then enters the condenser, where it rejects this heat. In heating mode, this heat warms the building's heating circuit; in cooling mode, it is expelled outdoors. Finally, the now-liquid refrigerant passes through an expansion valve, a restriction that drops its pressure sharply. This pressure drop causes some liquid to vaporise, and the cold mixture re-enters the evaporator, completing the cycle.

The refrigerant itself does no work; it is merely the medium that carries energy around the circuit. The compressor drives the cycle by consuming electrical energy. The efficiency of the system,measured as coefficient of performance (COP),depends on the refrigerant's thermodynamic properties and how well the cycle is controlled.

What are the common residential refrigerants and their environmental impact?

Refrigerants differ widely in their global warming potential (GWP), flammability, and suitability for different applications. The choice of refrigerant in new heat pumps has shifted dramatically as environmental regulations tighten.

Refrigerant	GWP (100-year)	Safety Class	Flammability	Typical Use
R410A (HCFC)	2088	A1	Non-flammable	Older systems being phased out
R32 (HFC)	675	A2L	Mildly flammable	Transitional replacement, common in 2020s systems
R290 (Propane)	3	A3	Highly flammable	Monobloc units and small sealed systems
R744 (CO2)	1	A1	Non-flammable	Specialist transcritical systems, emerging

R410A dominated residential heat pumps for two decades but has a GWP equivalent to the warming effect of 2,088 kg of CO2. R32 offers roughly one-third the climate impact but is still a hydrofluorocarbon (HFC) with significant warming potential. R290, refrigerant-grade propane, has a GWP near zero and outstanding thermodynamic efficiency, but its classification as a highly flammable gas (ASHRAE safety class A3) demands careful installation. R744, which is simply CO2, has a GWP of 1 (the baseline) and is non-flammable; however, it requires higher pressures and specialised compressors, limiting its current use to niche applications.

Refrigerant Safety Classifications and Handling

Safety Class	Flammability Description	Examples	Special Installation Requirements
A1	Non-flammable, low toxicity	R410A, R744 (CO2)	Standard installation; F-Gas certification required for handling
A2L	Mildly flammable, low toxicity	R32, R454B	Leak detection sensors required; minimum room size; clearances from ignition sources
A3	Highly flammable, low toxicity	R290 (propane), R600a (isobutane)	Sealed monobloc units preferred; strict clearances per manufacturer; ventilation requirements; F-Gas certification mandatory

The safety class determines both how the refrigerant charge may be limited and what installation precautions are required. Flammable refrigerants (A2L, A3) demand more stringent design, testing, and installation verification, but their environmental benefits justify the added complexity when correctly managed.

How does EU F-gas Regulation affect refrigerant choice?

The EU Regulation (EU) 2024/573 on fluorinated greenhouse gases, which entered force in March 2024, is the regulatory driver reshaping refrigerant selection across Europe. It accelerates the phase-down of high-GWP hydrofluorocarbons (HFCs) including R410A and R32.

From 2025, strict quotas and service restrictions apply to systems using refrigerants with GWP greater than 2,500. From 2026, these restrictions extend to air conditioning and heat pump equipment. Most significantly, from 2027, all new self-contained air-to-water and air-to-air heat pumps up to 12 kW must use refrigerants with GWP below 150. This deadline effectively eliminates R410A and R32 from new residential heat pumps across the EU and mandates transition to low-GWP alternatives.

The regulation also requires that all work involving refrigerant circuits,including leak detection, charging, and recovery,be performed exclusively by technicians holding valid F-Gas certification. This is true whether the system is a sealed monobloc unit or a split system. The certification requirement reflects both environmental responsibility (preventing leakage and atmospheric release) and safety, especially for flammable refrigerants like R290.

What is the difference between monobloc and split heat pump units?

Heat pump systems fall into two categories based on where the refrigerant circuit is sealed and charged. Understanding this distinction is crucial for installation, maintenance, and refrigerant safety.

A monobloc heat pump is a single, factory-sealed outdoor unit containing the compressor, evaporator, condenser, and all refrigerant charge. The entire system arrives pre-charged and ready to connect to the heating circuit (hot water pipes in an air-to-water system) or to the heating/cooling distribution system. Because the refrigerant charge is sealed at the factory, no on-site refrigerant handling is required. This approach eliminates the need for certified technicians to charge the system and drastically reduces the risk of leakage during installation. Monobloc units are ideal for flammable refrigerants such as R290, as the sealed design contains any potential hazard.

A split system separates the compressor and condenser (outdoor unit) from the evaporator (indoor unit). The two are connected by refrigerant pipework, and the charge must be calculated and adjusted on-site by a certified technician based on the pipe length and system configuration. Split systems allow flexibility in placement and have long been the standard for retrofit installations. However, they require refrigerant handling expertise and present a higher risk of leakage if connections are not properly sealed and tested.

For most residential buildings in Slovakia using air-to-water or air-to-air heat pumps with low-GWP refrigerants, monobloc designs are becoming the norm, especially where R290 is specified.

What safety and certification requirements apply to refrigerant handling?

Refrigerant management is strictly regulated because escaped refrigerant damages the ozone layer (though most modern refrigerants do not) and contributes to climate warming. Additionally, flammable refrigerants like R290 and mildly flammable ones like R32 require specific installation safeguards.

Any technician working with refrigerant circuits must hold an F-Gas certification issued under EU Regulation (EU) 2024/573. This applies to commissioning new systems, diagnosing leaks, recharging, and decommissioning. The certification process validates understanding of safe handling, environmental compliance, leak detection methods, and refrigerant recovery procedures.

For systems using flammable refrigerants, additional installation rules apply. Safety standards EN 378 and IEC 60335-2-40 define clearances and restrictions based on the refrigerant's charge quantity, flammability class, and the room volume where the unit is located. The manufacturer's installation manual specifies the protection zone that must surround an R290 outdoor unit, which must remain free from windows, doors, ventilation openings, drains, and ignition sources. This protection zone ensures that if refrigerant were ever to leak, it cannot accumulate in occupied spaces or near ignition sources.

Certified technicians are responsible not only for safe handling but also for verifying that installed systems comply with these clearance and ventilation rules, as set by the equipment manufacturer and the applicable European standards.