IN SHORT
Ammonia (NH₃/R717) It has a GWP of 0 and is among the most energy-efficient refrigerants for industrial refrigeration systems. An ammonia refrigeration system achieves a higher COP in many industrial applications than traditional HFC refrigerants such as R134a, R404A, or R507A. This has made it the preferred choice for large refrigeration and freezer installations for decades. Due to its toxicity and slight flammability, ammonia is classified as B2L (higher toxicity, low flammability) according to ISO 817/ NEN-EN 378. This requires specific safety measures and expert personnel.
CO₂ (R744)It has a GWP of just 1 and has become the standard for applications in the food industry, logistics centers, and cold/freezer storage facilities. The refrigerant is non-flammable and classified as A1 (non-toxic and non-flammable) according to ISO 817/ NEN-EN 378. However, high concentrations of CO₂ can pose an asphyxiation risk. An important characteristic of CO₂ systems is that they operate at significantly higher pressures than conventional refrigerant systems. Due to the high operating pressures and specific safety aspects of CO₂ installations, NPR 7601 is frequently used in the Netherlands in addition to ISO 817/ NEN-EN 378. This practical guideline provides tools for the safe application of CO₂ as a refrigerant in refrigeration systems and heat pumps. Thanks to its proven reliability, high energy efficiency, and minimal environmental impact, CO₂ is increasingly being used in large-scale refrigeration and heat pump systems.
Hydrocarbons (HCs)Such as propane (R290) and isobutane (R600a), combine a very low climate impact (GWP < 5) with excellent energy performance. This makes them particularly suitable for heat pumps, commercial refrigeration, and compact refrigeration systems. The downside is the high flammability of hydrocarbons. Therefore, many hydrocarbons, including propane (R290) and isobutane (R600a), are classified as safety class A3 according to ISO 817/ NEN-EN 378. In combination with the requirements of NEN-IEC 60335-2-40, this leads to limitations on the maximum permissible refrigerant charge and necessitates additional safety measures. For the practical application of flammable refrigerants in the Netherlands, NPR 7600 is also frequently used, which includes additional guidelines for design, setup, management, and safety provisions.
Together, ammonia, CO₂, and hydrocarbons form the main natural alternatives to synthetic F-gases. They offer a combination of low environmental impact, high energy efficiency, and future-proof sustainability within increasingly stringent European regulations.
As a specialist in industrial refrigeration technology, Nijssen has been designing and implementing systems based on NH₃, CO₂, and natural refrigerants for the food industry and logistics sector for decades.
Many companies only discover too late that a refrigeration system is no longer future-proof. By then, replacement costs are often higher, and the options are more limited.
Is your refrigeration system still running on R404A or R507A? Then the search for a future-proof alternative is becoming increasingly urgent. Due to the European F-Gas Regulation, these HFC refrigerants are being phased out more rapidly, making synthetic refrigerants scarcer, more expensive, and less future-proof.
A timely transition prevents unexpected costs due to refrigerant scarcity, stricter regulations, and unplanned replacement investments.
The choice for a new refrigerant is therefore not a technical detail, but a strategic investment for the next 15 to 20 years. Natural refrigerants are at the top of this list. They have a very low climate impact, are not subject to the same HFC phase-down, and – if applied correctly – can perform more favorably in terms of energy consumption, maintenance, and Total Cost of Ownership (TCO). In this article, we compare the three main natural alternatives: ammonia (NH₃/R717), CO₂ (R744), and hydrocarbons such as propane (R290). We assess them based on the practical criteria that matter: cooling capacity, safety, investment and operating costs, regulations, and suitability per application.
Many installations that were modern ten years ago will soon no longer meet the economic realities of the F-gas phase-down. As a result, choosing a natural refrigerant is increasingly becoming a business necessity rather than just a sustainability choice.
Ammonia (NH₃/R717), CO₂ (R744), and hydrocarbons (HCs) such as propane (R290) are not new inventions. These natural refrigerants have been used in refrigeration technology for over a century and have amply proven their reliability.
A significant advantage is that they fall outside the European HFC quotas (Regulation EU 2024/573) and are not affected by the ongoing phase-down of synthetic refrigerants. This offers greater long-term certainty. While an installation using natural refrigerants can easily last 20 to 25 years without the risk of refrigerant phase-out, HFC installations are increasingly facing scarcity, price increases, and additional regulations throughout their lifespan.
From an environmental perspective, natural refrigerants also have a clear advantage. The climate impact of a refrigerant is expressed in its Global Warming Potential (GWP), with CO₂ (R744) having a reference value of 1. For comparison: R404A has a GWP of 3,922, while ammonia (NH₃/R717) has a GWP of 0, CO₂ a GWP of 1, and propane (R290) a GWP of just 3. Consequently, none of these natural refrigerants fall under the European HFC phase-down.
On the other hand, natural refrigerants often require a higher initial investment than a comparable HFC installation. Specific knowledge and experience are also required for design, installation, and maintenance. However, for organizations that look beyond the purchase price alone, the Total Cost of Ownership (TCO) over a 20-year period often proves to be more favorable than for an installation using synthetic refrigerants.
For decades, ammonia (NH₃/R717) has been the standard for industrial refrigeration systems. This refrigerant has a GWP of 0 and an ODP of 0, making it one of the most energy-efficient solutions currently available. Under comparable operating conditions, ammonia typically delivers a 3 to 5 percent higher COP than R134a, which translates into demonstrable energy savings over the entire lifespan of the installation.
According to ISO 817/ NEN-EN 378, ammonia (NH₃/R717) is classified as B2L: toxic and mildly flammable. In practice, this requires a well-considered safety approach, including a separate machinery room, continuous leak detection, safety ventilation, and qualified personnel. In the Netherlands, ammonia installations fall under the guidelines of PGS 13, and additional requirements may apply regarding risk assessment and explosion safety. Modern low-charge designs significantly limit the refrigerant charge, further reducing risks without compromising performance.
NH₃ is primarily used in larger industrial installations with a cooling capacity of approximately >500 kW. Typical applications include food processing, cold and freezer storage, distribution centers, process cooling, breweries, and the chemical industry. Although the initial investment is generally higher than for a comparable HFC installation, operating costs are often lower due to high efficiency, long lifespan, and the absence of future refrigerant costs resulting from HFC regulations.
Since 1948, Nijssen has realized refrigeration installations for food producers, logistics centers, and process industries both domestically and internationally.
With a GWP of 1, carbon dioxide (CO₂, R744) has one of the lowest climate impacts of all available refrigerants. Partly because of this, CO₂ has become a widely used solution in the food industry, cold and freezer logistics, distribution centers, and supermarket refrigeration over the past decade.
Depending on the application, CO₂ can be used in various ways:
Subcritical systemsIn subcritical operation, CO₂ condenses below the critical temperature of 31°C. These systems are widely used for deep-freeze storage and low-temperature applications down to approximately -45°C. To remain below the critical temperature, a second cooling circuit is often required, such as an ammonia system or a chilled water circuit.
Transcritical SystemsWhen the ambient temperature rises and exceeds the critical temperature, the system operates transcritically. Operating pressures of up to approximately 120 bar are common in this mode, and the traditional condenser is replaced by a gas cooler. This requires specific material choices, pressure-resistant components, and a design compliant with the requirements of NEN-EN 378. In the Netherlands, NPR 7601 provides additional practical guidelines for the safe application of this standard, including aspects of installation design, ventilation, detection, and risk assessment. Thanks to technological developments, modern transcritical CO₂ systems are highly energy-efficient in the Dutch climate.
CO₂ as a Secondary RefrigerantCO₂ can also function as a secondary refrigerant. In this configuration, liquid CO₂ is circulated through refrigeration or freezer rooms to absorb heat and transfer it to a central refrigeration system, often based on ammonia (NH₃). This concept combines the high efficiency of ammonia with the safe distribution of CO₂ in the refrigerated spaces.
NH₃/CO₂ Cascade SystemsNH₃/CO₂ cascade systems are regularly used for freezing and deep-freezing applications. In these systems, an ammonia plant handles heat rejection on the high-temperature side, while CO₂ is used for the low-temperature stage. Both systems are linked via a cascade condenser. This configuration enables very low process temperatures with high efficiency and a limited refrigerant charge.
In temperate climates like the Netherlands, modern CO₂ systems are highly competitive in terms of energy performance. As a result, CO₂ has become a proven and future-proof standard for refrigeration and freezer logistics, distribution centers, fresh produce storage, and food processing. For process cooling above 0°C, ammonia generally remains the most efficient solution.
In recent years, Nijssen has implemented various CO₂ and NH₃/CO₂ systems for the food industry and logistics sector. An example is the NH₃/CO₂ system for Lidl Moerdijk, which, upon completion in 2013, was part of Europe's largest banana ripening facility.
Hydrocarbons (HCs), of which propane (R290) is the best known, combine a very low environmental impact with excellent thermodynamic properties. Propane has a GWP of just 3 and an ODP of 0, making it an attractive alternative to synthetic refrigerants in refrigeration and heat pump applications.
According to ISO 817/NEN-EN 378, many hydrocarbons (HCs), including propane (R290) and isobutane (R600a), fall into safety class A3: low toxicity and high flammability. For this reason, specific requirements apply to design, installation, ventilation, and the limitation of ignition sources. For the practical application of flammable refrigerants in the Netherlands, NPR 7600 is also frequently used, which includes additional guidelines for the design, setup, commissioning, management, maintenance, and safety provisions of refrigeration systems and heat pumps using flammable refrigerants. In accordance with NEN-IEC 60335-2-40, the permitted refrigerant charges depend on the application, installation space, and safety measures taken.
Hydrocarbons are often used in indirect cooling systems, chillers, and heat pumps. Thanks to their favorable thermodynamic properties, their energy performance is comparable to or better than many traditional HFC refrigerants, while their climate impact is significantly lower.
For higher capacities, systems are often built with multiple independent circuits. This increases operational reliability but also entails more components, control technology, and maintenance points. As the required cooling capacity increases, the complexity of a propane system therefore grows.
For small and medium-sized refrigeration and heat pump applications, propane often offers an excellent combination of energy efficiency, sustainability, and investment costs. However, for large-scale industrial refrigeration systems, designers more often opt for ammonia or CO₂, as these refrigerants are better suited for high capacities and large refrigerant charges.
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Natural Refrigerants Overview
Ammonia (NH₃) is a toxic refrigerant and is therefore used within a strict safety framework. An important advantage is that ammonia emits a characteristic odor even at very low concentrations, allowing leaks to be detected quickly. Modern installations are also equipped with continuous leak detection, safety ventilation, and automatic security systems. In the Netherlands, additional requirements apply based on, among others, PGS 13 and ATEX directives. Consequently, an ammonia installation requires specialized design, expert execution, and professional management. With correct design and maintenance, ammonia has been a proven and reliable refrigerant for industrial applications for decades.
In most cases, no. CO₂ and ammonia installations operate with different pressures, components, piping materials, and safety features than traditional HFC systems. A complete switch to a natural refrigerant therefore often means extensive renovation or replacement of the installation. As a temporary solution, an HFC or HFO blend with a lower GWP, such as R449A, can sometimes be chosen. This reduces the climate impact without major modifications to the installation. However, due to the further tightening of F-gas regulations, this is usually an interim step and not a long-term solution.
That depends on the application. The correct comparison is made based on the Total Cost of Ownership (TCO) and not solely on the initial investment. Ammonia (NH₃) generally has the highest investment costs but often offers the lowest operating costs due to its high efficiency and the absence of HFC-related refrigerant costs. For many logistics and food applications, CO₂ (R744) strikes an attractive balance between investment, performance, and future-proofing. Hydrocarbons (HCs) offer excellent energy performance and a very low environmental impact but have limitations for larger capacities due to flammability and maximum permissible refrigerant charges. The most economical choice varies per project. Factors such as cooling capacity, temperature range, operating hours, available space, and safety requirements ultimately determine which solution yields the lowest costs over its entire lifespan.
Ammonia (NH₃/R717), CO₂ (R744), and hydrocarbons (HCs) each offer a future-proof alternative to synthetic refrigerants. Which solution is best suited depends on the application, desired cooling capacity, temperature requirements, available space, and applicable safety frameworks.
For large industrial installations, ammonia remains the benchmark for energy efficiency and reliability. CO₂ has become the standard for food, logistics, and refrigeration-freezing applications, while hydrocarbons are an attractive choice for smaller refrigeration and heat pump systems where a limited refrigerant charge is possible.
The choice of a refrigerant is therefore not a standard decision but a trade-off between performance, safety, investment costs, and future-proofing. A well-designed installation not only yields the lowest operating costs but also prevents you from facing future limitations due to regulations or refrigerant availability. Unsure about NH₃, CO₂, or hydrocarbons? In many projects, the optimal choice only becomes clear when cooling capacity, temperature range, operating hours, and safety requirements are assessed together. That's why we start almost every project with a technical and economic feasibility analysis.
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