How to Select the Right Refrigerant for a Refrigeration System

Refrigeration is the backbone of the dairy industry. From the moment milk leaves the udder to the time butter, cheese, or yogurt reaches the consumer, temperature control is non-negotiable. But here’s the thing – the performance of any refrigeration system depends heavily on the refrigerant it uses. Choosing the wrong one can lead to higher energy bills, safety hazards, or even environmental damage. So, how do you select the right refrigerant? Let’s break it down.

What is a refrigerant and why does it matter? 🔗

A refrigerant is a fluid that circulates within a refrigeration system, absorbing heat at low temperatures during evaporation and releasing it at high temperatures during condensation. In simpler terms, it’s the substance that actually does the “cooling” inside the system. The choice of refrigerant directly affects how efficiently the system operates, how safe it is for workers, and what kind of environmental footprint the operation leaves behind.

Refrigerants are broadly classified into two types. Primary refrigerants are the working fluids used directly in vapour compression or absorption systems – ammonia and Freon are common examples. Secondary refrigerants, such as brine solutions (water mixed with ethylene glycol or propylene glycol), don’t undergo a phase change themselves but transport thermal energy from one location to another. In dairy plants, the focus is almost always on selecting the right primary refrigerant.

Key properties to consider when selecting a refrigerant 🔗

There is no single “perfect” refrigerant. Every option involves trade-offs. However, engineers typically evaluate refrigerants based on a few core categories: thermodynamic performance, safety, environmental impact, and cost-effectiveness. Let’s look at the most important properties.

Boiling point 🔗

The boiling point of a refrigerant determines the temperature at which it evaporates and starts absorbing heat. For refrigeration applications, a low boiling point is desirable because it allows the refrigerant to evaporate at temperatures well below the target cooling temperature. Ammonia, for example, has a boiling point of about −33.3°C at atmospheric pressure, which makes it well-suited for the low-temperature requirements of dairy processing and cold storage.

Latent heat of vaporization 🔗

Latent heat refers to the amount of heat a refrigerant can absorb during its phase change from liquid to gas. A higher latent heat of vaporization means the refrigerant can absorb more heat per kilogram, making the system more efficient and reducing the amount of refrigerant that needs to circulate through the system. Ammonia has an exceptionally high latent heat of vaporization – approximately 1368 kJ/kg – which is significantly higher than most synthetic refrigerants. This is one of the primary reasons it is favoured for large-scale industrial and dairy applications.

Operating pressures 🔗

The evaporation pressure of a refrigerant should ideally be at or slightly above atmospheric pressure. If it drops below atmospheric pressure, there is a risk of air and moisture leaking into the system, which can cause ice blockages and reduce efficiency. At the same time, the condensation pressure should not be excessively high, as that would require stronger (and more expensive) system components. The pressure ratio between condensation and evaporation pressures should also be kept small for optimal compressor performance.

Safety: toxicity and flammability 🔗

Safety is a critical factor, especially in facilities where workers are present in or near the refrigeration equipment. Refrigerants are evaluated for their toxicity (how harmful they are if inhaled or contacted) and flammability (whether they can ignite or explode under operating conditions). Some refrigerants, like ammonia, are toxic and mildly flammable but have a strong, pungent odour that serves as a natural self-alarming property, making leaks easy to detect. Others, like most Freon-type refrigerants, are non-toxic and non-flammable, which makes them safer for use in smaller or less-controlled environments.

Environmental impact: ODP and GWP 🔗

Two key environmental metrics guide refrigerant selection today. Ozone Depletion Potential (ODP) measures how much a substance contributes to the destruction of the stratospheric ozone layer. Global Warming Potential (GWP) indicates how much a substance contributes to global warming compared to carbon dioxide. Under international agreements like the Montreal Protocol, ozone-depleting substances such as CFCs and HCFCs have been phased out or are being phased down. Modern refrigerant selection strongly favours substances with zero or near-zero ODP and low GWP.

Other important factors 🔗

Beyond the major properties listed above, several additional characteristics influence refrigerant selection. The refrigerant should have low viscosity to minimise flow resistance in the piping. It should be chemically stable at high operating temperatures and should not corrode or degrade the metals and sealing materials used in the system. Compatibility with compressor lubricants is also essential – for instance, newer HFC refrigerants require polyolester (POE) oils rather than the mineral oils used with older refrigerants. Finally, cost and availability play a practical role. A refrigerant that is cheap, widely available, and easy to handle will always have an advantage in the field.

Ammonia: the preferred refrigerant for dairy plants 🔗

Ammonia (NH₃), also designated as R-717, has been used as a refrigerant since the late 19th century and remains the dominant choice for large-scale industrial refrigeration, including dairy processing. There are several compelling reasons for this.

High efficiency 🔗

Ammonia’s combination of a low boiling point and high latent heat of vaporization gives it outstanding thermodynamic performance. At full capacity, ammonia refrigeration systems can be up to 20% more efficient than systems using other common refrigerants. This efficiency advantage becomes even more pronounced in low-temperature applications – exactly the kind of conditions found in dairy cold storage and ice cream production. Better efficiency translates directly into lower electricity consumption and reduced operating costs.

Zero environmental impact 🔗

Ammonia has an ODP of zero and a GWP of zero (or near zero). It does not contribute to ozone layer destruction and has negligible impact on global warming. Compared to synthetic refrigerants like R-404A, which has a GWP of nearly 4,000, ammonia is in a league of its own when it comes to environmental sustainability. This makes it fully compliant with both the Montreal Protocol and evolving F-gas regulations aimed at reducing greenhouse gas emissions from refrigeration systems.

Cost-effectiveness 🔗

Ammonia is relatively inexpensive to produce and widely available. Its cost can be as low as one-tenth of conventional HFC refrigerants. Because of its high efficiency, less ammonia is needed to achieve the same cooling effect, which further reduces operational costs. Ammonia-based systems also tend to have a longer operational lifespan when properly maintained, making them a sound long-term investment for dairy facilities.

Applications in dairy processing 🔗

In a dairy plant, ammonia refrigeration is used across multiple stages. Immediately after milking, milk needs to be cooled to below 4°C to prevent bacterial growth and preserve quality. Ammonia chillers, combined with evaporative condensers and cooling coils, handle this task efficiently. Beyond initial cooling, ammonia systems maintain controlled temperatures in pasteurization areas, cheese production rooms, yogurt fermentation units, cold storage warehouses, and ice cream production lines.

Challenges with ammonia 🔗

Despite its advantages, ammonia is not without drawbacks. It is toxic – exposure to high concentrations can cause serious injury or even death. It is also mildly flammable at concentrations between 15% and 28% in air. Ammonia systems require specialised materials (such as stainless steel piping, since ammonia is corrosive to copper) and must be designed, installed, and maintained by certified personnel following strict safety codes (e.g., ASME, IIAR, OSHA). Facilities using large quantities of ammonia – typically over 10,000 pounds – are also required to have a process safety management (PSM) plan in place. These requirements add to the upfront complexity and cost of ammonia systems, though the long-term savings usually justify the investment.

Freon and synthetic refrigerants: when and why they are used 🔗

Freon is a brand name (originally by DuPont, now Chemours) for a family of halocarbon refrigerants, including CFCs, HCFCs, and HFCs. While older Freon variants like R-12 (a CFC) and R-22 (an HCFC) have been phased out due to their ozone-depleting properties, newer options like R-134a (an HFC) remain widely used, particularly in smaller-scale refrigeration and air conditioning systems.

Advantages of Freon-type refrigerants 🔗

The biggest advantage of Freon-based refrigerants is their safety profile. Most are non-toxic and non-flammable, which eliminates the need for specialised safety equipment, training, and emergency response protocols. This makes them practical for residential use, small commercial establishments, retail food display cases, and smaller dairy operations where dedicated ammonia-handling infrastructure is not feasible. Freon systems are also easier to service – technicians and replacement parts are more widely available, especially in remote areas.

Limitations of Freon 🔗

Freon refrigerants generally have lower thermodynamic efficiency compared to ammonia, meaning they consume more energy to achieve the same cooling effect. Many HFC-type Freons also carry a significant global warming potential. R-134a, for instance, has a GWP of about 1,430, while R-404A has a GWP close to 3,922. As a result, international regulations, including the Kigali Amendment to the Montreal Protocol, are progressively phasing down HFC usage. The industry is shifting toward newer HFC/HFO blends (such as R-448A and R-449A) that offer lower GWP while maintaining acceptable performance.

Where Freon makes sense in dairy 🔗

For small dairy farms with a single bulk tank and a basic chiller unit, a Freon-based system is often the practical choice. The cooling demands are modest, the safety risks are low, and the installation and maintenance costs are manageable. Freon cold storage systems can maintain temperatures ranging from around +5°C (suitable for fresh dairy products) down to −25°C or lower (for frozen goods like ice cream). The key trade-off is higher energy consumption and a greater environmental footprint compared to ammonia.

Comparing ammonia and Freon: a quick overview 🔗

When deciding between ammonia and Freon for a dairy refrigeration system, the choice largely depends on the scale of operations, safety infrastructure, and regulatory environment. Ammonia is ideal for large-scale plants where cooling demands exceed 200 tons of refrigeration capacity. Its superior efficiency, lower operating cost, and zero environmental impact make it the standard for industrial dairy operations. Freon, on the other hand, suits smaller operations where simplicity, safety, and lower initial investment are priorities. As a general rule, any cooling need over 200 tons is a strong candidate for ammonia, while smaller systems lean toward HFC or HFC/HFO alternatives.

The future of refrigerant selection in dairy 🔗

The refrigeration industry is undergoing a significant transition. With stricter environmental regulations phasing down high-GWP refrigerants, the trend is clearly moving toward natural refrigerants – ammonia, CO₂, and hydrocarbons – that have minimal or no impact on the ozone layer and global warming. Low-charge ammonia systems are gaining popularity as they reduce the total amount of ammonia on-site (with charge-to-capacity ratios as low as 3-6 pounds per ton of refrigeration), addressing both safety and regulatory concerns. Meanwhile, smart controls and variable frequency drives are helping both ammonia and Freon systems operate more efficiently, reducing energy consumption and emissions further.

For dairy operations of all sizes, the message is clear: refrigerant selection is not just a technical decision – it has real implications for energy costs, worker safety, product quality, and environmental responsibility. Making an informed choice today can save money and contribute to a more sustainable dairy industry tomorrow.

What do you think? How should small and medium dairy farms balance the lower upfront cost of Freon systems against the long-term efficiency and environmental benefits of ammonia? As low-charge ammonia technology becomes more accessible, do you see it eventually replacing Freon in smaller dairy operations as well?

References

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3. https://www.araner.com/blog/what-is-ammonia-refrigeration-everything-you-need-to-know
4. https://www.epa.gov/greenchill/advanced-refrigeration-technologies
5. https://www.araner.com/blog/ammonia-refrigeration-choice-industrial-refrigeration
6. https://www.designingbuildings.co.uk/wiki/Refrigerant_selection
7. https://www.intarcon.com/en/ammonia-refrigeration-nh3-r717/
8. https://www.gea.com/en/stories/ammonia-the-natural-choice-to-reduce-harmful-industrial-emissions/
9. https://foodplantengineering.com/services/food-process-facility-design/facility-design/refrigeration