Optimizing Efficiency: Refrigerants in Industrial Heat Pumps
The choice of refrigerant is one of the most important factors determining the technical and economic performance of an industrial heat pump: it has a decisive influence on the temperature lifts and heat sink temperatures that can be achieved.
At the same time, the specific waste heat source, individual safety requirements, and the applicable regulatory framework all play a role in determining which refrigerants are viable for a specific application. Particularly in the industrial high-temperature range, there is no universal solution. To understand why, it is first necessary to understand how refrigerants work – and where they differ.
Refrigerants and their role in industrial heat pumps
Refrigerants are the working fluid of an industrial heat pump. Their central function is to absorb heat from an available source, raise it to a higher temperature level, and deliver it as usable process heat or process steam.
This requires a closed thermodynamic cycle: the liquid refrigerant absorbs heat from a heat source at low temperature, causing it to evaporate. Electrically driven compressors then compress the now gaseous refrigerant, raising it to a higher pressure and therefore a higher temperature level. The refrigerant subsequently transfers its thermal energy to the heat sink, cools down and condenses, and the cycle begins again.
Therefore, the refrigerant is a central design parameter for industrial applications: it determines which source temperatures can be utilised, which target temperatures are achievable, and what temperature lift is technically and economically viable. Refrigerant selection is particularly critical when utilizing waste heat, which is frequently available at comparatively low but sometimes significantly variable temperature ranges of 30 to 80 °C, while process heat or steam at temperatures of 120, 160, or 200 °C may simultaneously be required. How efficiently the required temperature lift can be achieved depends substantially on the properties of the refrigerant.
Which properties make a refrigerant suitable?
Whether a specific refrigerant is suited to a given industrial heat pump application is not determined by any single parameter. Rather, it depends on the interplay of several thermodynamic, safety-related, and economic factors. Particularly when utilizing industrial waste heat as a source and targeting high process temperatures, a project-specific assessment and design approach is therefore essential.
Thermodynamic properties
Among the key properties and selection criteria are the critical temperature and critical pressure of a refrigerant. These values indicate up to which temperature and pressure range a refrigerant can be usefully condensed, and therefore up to which temperature and pressure range it can be employed in the heat pump process.
The specific heat capacity and latent heat of a refrigerant determine how much thermal energy can be transported per kilogram of refrigerant. The more favourable these values, the more compact or efficient the system can be designed.
Density and thermal conductivity primarily influence the dimensioning of pipework, heat exchangers, and compressors within the system. Both values therefore also affect energy consumption and overall system efficiency.
Efficiency and performance
The efficiency and performance of an industrial heat pump depend not only on the thermodynamic properties of the refrigerant: the interaction between heat source, inlet temperature, and desired target temperature plays a major role – and as a general rule, the greater the required temperature lift between the waste heat source and the target temperature, the higher the demands placed on the refrigerant.
The efficiency and performance of the heat pump are expressed in its COP (Coefficient of Performance), which is, however, also substantially influenced by the system design. The use of high-performance refrigerants does not automatically translate into high overall efficiency.
Safety
Safety considerations also play an important role in selecting the appropriate refrigerant. The safety classification of a refrigerant under ISO 817 / EN 378 provides information on both flammability and toxicity – two fundamental factors in any safety assessment.
Letters describe toxicity:
- A = lower toxicity
- B = higher toxicity
Numbers indicate flammability:
- 1 = non-flammable
- 2L = mildly flammable / low burning velocity
- 2 = flammable
- 3 = highly flammable
Using this system, refrigerants can be classified as, for example, A1 (low toxicity, non-flammable) or A3 (low toxicity, highly flammable).
In industrial applications, the safety classification in turn influences certain aspects of system design, including required safety distances, gas detection and ventilation systems, explosion protection, and applicable permit requirements. In addition to flammability and toxicity, the operating pressure level is also relevant, as high pressures may impose additional requirements on components, pipework, and safety devices.
Economic viability and availability
Beyond the technical and physical properties, price, availability, and security of supply also play an important role in refrigerant selection. Regulatory developments can affect the cost and availability of certain substances.
Material compatibility and long-term behaviour
Not every refrigerant is equally compatible with the materials, seal types, lubricants, or other system components. The chemical stability and material compatibility of the refrigerant affect the service life of the entire system – and the high-temperature range, with its elevated pressure levels and thermal stresses, is particularly demanding in this respect.
Refrigerant classes: Synthetic and natural refrigerants at a glance
In practice, selecting the appropriate refrigerant is typically based on a structured comparison of available options with regard to thermodynamic properties, global warming potential (GWP), ozone depletion potential (ODP), safety classifications, and regulatory requirements – combined with a consideration of the cost of the refrigerant itself and the resulting implications for system design and capital expenditure.
The overview table below provides an initial orientation on the most important parameters – it is not intended to replace, and cannot replace, a detailed, project-specific engineering assessment.
Natural Refrigerants
Natural refrigerants are characterised by very low GWP values, making them regulatorily secure over the long term. They frequently offer excellent thermodynamic properties, though they are sometimes subject to more demanding safety requirements.
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NATURAL REFRIGERANTS
| Refrigerant | Substance class | Safety class (ISO 817) | GWP (F‑Gas‑VO 2024/573) | ODP | Tcrit (°C) | Pcrit (bar) | Boiling point at 1 bar (°C) | Max. hot water temperature (°C) | Process steam suitable? | Price level | Regulatory certainty | Notes / Limitations |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| R290 (Propane) | Hydrocarbon | A3 | 0.02 | 0 | 96.7 | 42.5 | -42.1 | -60 | No | Low | High | Flammable (A3); ATEX measures may be required; industrially established |
| R744 (CO₂) | Inorganic | A1 | 1 | 0 | 31.1 | 73.8 | −78 (Sublim.) | ~100 | No | Low | No | Transcritical operation; very high pressure requirements |
| R717 (NH3) | Inorganic | B2L | 0 | 0 | 132.3 | 113.5 | -33.3 | ~145 | Yes | Low | High | Can be toxic at high concentrations; ATEX measures may be required; very high COP |
| R600a (Isobutane) | Hydrocarbon | A3 | 0 | 0 | 134.7 | 36.4 | -11.7 | ~125 | Yes | Low | High | Flammable (A3) |
| R600 (n-Butane) | Hydrocarbon | A3 | 0.006 | 0 | 151.9 | 38.0 | -0.5 | ~140 | Yes | Low | High | Flammable (A3); higher Tcrit than isobutane |
| R601a (Isopentane) | Hydrocarbon | A3 | 0 | 0 | 187.2 | 33.8 | +27.7 | ~180 | Yes | Low | High | Flammable (A3); higher Tcrit than isobutane |
| R601 (n-Pentane) | Hydrocarbon | A3 | 0 | 0 | 196.6 | 33.7 | +36.1 | ~185 | Yes | Low | High | Flammable (A3); auto-ignition threshold at 200 °C – no surface may exceed this temperature – limits max. hot water temperature |
| Cyclopentan | Hydrocarbon | A3 | 0 | 0 | 238.5 | 45.1 | +49.3 | ~200 | Yes | Low | High | Flammable (A3); very high Tcrit; niche HTHP application; primarily used as foam blowing agent |
Synthetic Refrigerants
Synthetic refrigerants of the newer generation – in particular HFOs (hydrofluoroolefins) and HFO blends – bridge the gap between conventional synthetic HFCs (hydrofluorocarbons) with their comparatively high GWP values and the more demanding natural refrigerant alternatives.
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SYNTHETIC REFRIGERANTS
| Refrigerant | Substance class | Safety class (ISO 817) | GWP (F‑Gas‑VO 2024/573) | ODP | Tcrit (°C) | Pcrit (bar) | Boiling point at 1 bar (°C) | Max. hot water temperature (°C) | Process steam suitable? | Price level | Regulatory certainty | Notes / Limitations |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| R454C | HFO/HFC-Gem. | A2L | 146 | 0 | 82.4 | 38.6 | -45.5 | ~70 | No | Medium | Medium to High (PFAS debate) | Mildly flammable (A2L); R32/R1234yf blend (21.5/78.5%); R404A/R22 replacement |
| R515B | HFO/HFC blend | A1 | 288 | 0 | ~103 | ~34.0 | -19.5 | ~100 | No | High | Medium (PFAS debate) | Non-flammable; R1234ze(E)/R227ea blend |
| R1234ze(E) | HFO | A2L | 1.37 | 0 | 109.4 | 36.3 | -19.0 | ~100 | No | Medium | Medium to High (PFAS debate) | Mildly flammable (A2L); widely used as R134a replacement |
| R1224yd(Z) | HCFO | A1 | 0.06 | 0.00012 | 155.0 | 33.3 | +14.0 | ~150 | Yes | High | Medium (PFAS debate) | Non-flammable; suitable R245fa alternative |
| R1233zd(E) | HCFO | A1 | 3.88 | 0.00034 | 166.5 | 36.2 | +18.3 | ~155 | Yes | Medium | Medium (PFAS debate) | Non-flammable; widely used in HTHP |
| R1336mzz(Z) | HFO | A1 | 2.08 | 0 | 171.3 | 29.0 | +33.4 | ~165 | Yes | High | Medium (PFAS debate) | Non-flammable; highest Tcrit among A1 HFOs |
- Safety class per ISO 817 / ASHRAE 34: First letter = toxicity (A = low chronic toxicity; B = higher toxicity). Number = flammability (1 = non-flammable; 2L = mildly flammable; 2 = flammable; 3 = highly flammable).
- GWP values per EU F-Gas Regulation 2024/573: For HFOs/HCFOs (Annex II Group 1) and hydrocarbons (Annex VI) based on IPCC AR6. Natural refrigerants fall outside the scope of the F-Gas Regulation.
- ODP (Ozone Depletion Potential) relative to R11 (trichlorofluoromethane) = 1. HFOs and hydrocarbons: ODP = 0. HCFOs contain chlorine and therefore have ODP > 0, though at very low levels. Sources: WMO Scientific Assessment of Ozone Depletion 2018 and relevant technical literature.
- Regulatory certainty: 'High' = natural refrigerants, no F-Gas/PFAS risk. 'Medium (PFAS debate)' = HFO/HCFO, currently legal and technically valid, but EU-level PFAS regulation under discussion – as of 2026.
- Price level: indicative value at standard market purchase volumes. May vary depending on supplier, availability, and quantity.
EU F-Gas Regulation: Phasing out fluorinated greenhouse gases
The revised EU F-Gas Regulation, which entered into force in 2024, significantly tightens the planned phase-down of fluorinated greenhouse gases: the objective is to move away largely from refrigerants with particularly high GWP values by 2050. While this gives rise to new considerations in project planning, the existing regulatory roadmap already provides guidance on the medium- to long-term viability of specific refrigerants.
For industrial heat pumps used in process heat generation, the F-Gas Regulation means:
- Conventional HFCs, such as R134a or R245fa, are no longer a viable option for industrial heat pumps in the medium to long term. New installations based on these substances therefore carry regulatory risk.
- HFOs with a GWP below 150, such as R1234ze(E), are less directly affected by the F-Gas Regulation. However, they are subject to the ongoing PFAS discussion (see below).
- Natural refrigerants are regulatorily unproblematic in the context of the F-Gas Regulation, given their low GWP values. They represent the safest long-term choice with regard to approval risks and regulatory requirements.
For investment decisions involving the typical operational lifetimes of industrial heat pumps (15 to 25 years) the regulatory resilience of the chosen refrigerant must be carefully considered.
The PFAS debate and its implications for refrigerant use
Per- and polyfluoroalkyl substances (PFAS), also known as "forever chemicals", are particularly persistent man-made chemical compounds that can accumulate in the environment and in living organisms. PFAS are currently the subject of complex and contentious political and media debate. The European Chemicals Agency (ECHA) has initiated proceedings to broadly restrict all non-essential PFAS applications – a process that would affect numerous industrial sectors.
HFOs and HFO blends also contain fluorinated carbon compounds and therefore fall under the chemical definition of PFAS. This means that even though they have significantly lower climate impacts than their HFC predecessors, they could potentially be captured by PFAS regulation if the regulatory framework does not explicitly exempt them.
A differentiated regulatory approach is the more likely outcome
As of today, HFO refrigerants are valid, approved, and widely used substances. No prohibitions currently exist that would prevent the use of HFO refrigerants. The PFAS debate at EU level is, however, complex and protracted, and its outcome remains open. Discussions among stakeholders include, for example, possible distinctions between persistent PFAS that are barely broken down naturally, and rapidly degradable fluorinated substances.
A further consideration is that the sheer scale of the potentially affected installed base would make a blanket PFAS ban on refrigerants considerably difficult to implement in practice. According to industry figures, many millions of air conditioning and heat pump systems are in operation across the EU alone, the vast majority of which use fluorinated refrigerants. The European Parliament's Committee on Industry, Research and Energy (ITRE) has also concluded, in the context of a dedicated study, that a broad ban on PFAS chemicals of the kind initially proposed by ECHA would not currently be technically or economically feasible. The refrigeration industry, the European Heat Pump Association (EHPA), and numerous industry associations have already made strong submissions in the public ECHA consultation, highlighting potential consequences including risks to the security of supply in critical infrastructure, significant costs for system operators, and the risk of stalling the European heat pump roll-out. These factors point strongly towards a differentiated regulatory approach that distinguishes between sectors.
Industrial heat pump systems are subject to more stringent safety requirements
Furthermore, not all systems should be treated as equivalent from a regulatory perspective. The relevant European standard EN 378 explicitly distinguishes between location types and occupancy categories: For residential buildings and public spaces (occupancy category A), particularly strict limits apply to the permissible refrigerant charge, as people without specialist knowledge may be present near the system in this category. For industrial machinery rooms (occupancy category C), charge limits are less restrictive, but considerably stricter technical and operational requirements apply – including leak detection, provisions for automatic emergency ventilation and safety shutdown, and regular tightness inspections. For larger systems, the leak monitoring requirements of the F-Gas Regulation and internal safety management systems add further layers of obligation.
The risk of uncontrolled refrigerant release from professionally designed and operated industrial systems is therefore structurally far lower than from the millions of small appliances installed in residential buildings or at private premises. This distinction underscores the relevance of a differentiated risk assessment and gives reason for confidence that industrial systems will not be regulated under the same criteria as the mass market in any future PFAS framework.
Classifying HFO refrigerants as a blanket risk factor would, in this context, be a premature and likely disproportionate step. At the same time, we are actively and closely monitoring developments – it is clear, for instance, that for any new installation based on HFO refrigerants, technically and economically realistic scenarios for a future refrigerant conversion should be kept in view. For projects with very long planning horizons or where risk aversion is high, the use of natural refrigerants – which we ourselves prefer – offers the greatest planning certainty.
Conclusion: Refrigerant selection is too important to leave to last
Selecting the right refrigerant is not a secondary detail decision – it is of high strategic, economic, and technical relevance. The target temperature level, the quality of the heat source, project-specific safety requirements, and both regulatory and economic perspectives must all be considered and assessed together.
Therefore, it becomes clear that there is no universally applicable refrigerant, and no single answer to the question of which refrigerant is best suited for use in industrial heat pumps. What is decisive is a professional, project-specific evaluation of all boundary conditions – from the waste heat source and the required process temperature levels through to the long-term regulatory outlook.
Which refrigerant is right for your project depends on your specific process parameters, the installation site, safety requirements, and a range of further factors. We would be pleased to support you throughout this process – from initial assessment to a fully operational system.
