Recirculating chillers are devices used to remove heat from equipment or processes by circulating a liquid coolant. These chillers are commonly employed in industrial, laboratory, and commercial settings to maintain controlled temperatures for various applications, such as cooling lasers, analytical instruments, or medical devices. Traditionally, these chillers have relied on synthetic refrigerants like hydrofluorocarbons (HFCs), which are potent greenhouse gases and have a high Global Warming Potential (GWP).

Propane, known as R290 in refrigeration terminology, is a natural hydrocarbon refrigerant. It has several advantages that make it an attractive alternative to conventional synthetic refrigerants:

1. Environmental Benefits

Propane has a low GWP of 3 and an Ozone Depletion Potential (ODP) of zero, making it far more environmentally friendly than many traditional refrigerants like R134a or R410A, which have GWPs in the hundreds or thousands. By switching to propane, industries can significantly reduce their carbon footprint and comply with increasingly stringent environmental regulations.

2. Energy Efficiency

Propane is highly energy-efficient due to its favourable thermodynamic properties. It has a high latent heat of vaporisation and excellent thermal conductivity, which allows for efficient heat transfer and cooling performance. This efficiency often translates to reduced energy consumption and lower operational costs for recirculating chillers.

3. Availability and Cost-Effectiveness

As a naturally occurring hydrocarbon, propane is widely available and cost-effective compared to many synthetic refrigerants. It is often produced as a by-product of natural gas processing and petroleum refining, making it a readily accessible option for various applications.

Despite its benefits, the use of propane as a refrigerant is not without challenges:

1. Flammability and Safety Requirements:

Propane is a highly flammable refrigerant, classified as an A3 refrigerant. This poses a potential safety risk that requires careful consideration, especially in environments where large quantities are used or stored. Additional safety measures may be required.

Additionally, the use of propane is subject to specific regulations and safety standards that vary by region and application. One critical aspect of these regulations involves room size limitations. For example, the charge size of propane refrigerant in a system is often directly related to the volume of the room where the equipment is installed. Small rooms may not be suitable for systems with larger refrigerant charges due to the risk of propane concentration reaching flammable levels in case of a leak. Proper risk assessments, including room size calculations and ventilation adequacy, must be performed to ensure safety compliance.

Logistical hurdles also arise in terms of transporting, storing, and handling propane-based systems. Due to its flammable nature, propane refrigerants require special handling, including appropriate packaging and labelling, as well as trained personnel to manage and maintain the equipment safely. These considerations can add complexity and cost to the supply chain and operational logistics for businesses.

2. Regulatory Restrictions

The use of propane is subject to regulatory restrictions, which may limit its application in specific settings. Regulatory bodies such as the European Union (EU), Environmental Protection Agency (EPA), and other regional authorities have established guidelines and standards, including maximum allowable refrigerant charge sizes, requirements for equipment design, and conditions for safe installation and use. Compliance with these standards is crucial, and businesses may need to invest in additional safety features or adjust their operations to meet local regulations.

3. System Design Considerations

Design adjustments are necessary to accommodate propane’s unique properties. For instance, heat exchangers and compressors must be appropriately sized to optimise propane’s thermal performance, and safety features must be integrated to address the risks associated with flammability. Proper material selection, enhanced safety mechanisms, and hermetically sealed components are essential to support safe and efficient propane use.

The exact charge limit for R290 in recirculating chillers can vary based on several key factors, including the chiller’s design, its intended application, and the environment where it will be installed. Here are the details that influence these considerations:

1. Design of the chiller:

Leak Prevention and Containment: The construction and engineering of the chiller are critical in determining how much R290 can be safely used. Chillers designed with robust leak prevention mechanisms, proper ventilation, and hermetically sealed components, and advanced leak detection systems contribute to enhanced safety, potentially allowing for higher charge limits.

2. Application of the Chiller:

Type of Environment: The type of application can dictate the charge limits due to safety requirements. For example, chillers used in industrial environments (like a dedicated equipment room or factory floor with restricted access) may have more flexibility in refrigerant charge limits compared to those used in general or residential environments where there is a higher risk of exposure to personnel.

Nature of the Process: If the chiller is used for processes that demand specific performance parameters, such as maintaining a very low or very stable temperature, the equipment may be engineered to accommodate a particular refrigerant charge that aligns with those needs.

3. Installation Environment:

Location (Indoor vs Outdoor): Equipment installed outdoors or in non-occupied areas may have different charge limits than equipment installed indoors or in occupied spaces. Outdoor installations, for example, may allow for higher charges because they typically have better ventilation and a reduced risk of accumulation of flammable gas in case of a leak.

Room Size and Ventilation: For indoor installations, the room’s size and ventilation rate are critical factors. Larger rooms with good ventilation can disperse refrigerant in case of a leak, potentially allowing for a higher refrigerant charge. In contrast, small, poorly ventilated rooms have stricter limits due to the higher risk of flammable concentrations building up.

4. Regional Standards and Regulations:

Compliance with Local Standards: Different regions have specific safety standards and regulations that set maximum allowable charges for flammable refrigerants. Compliance with these standards (such as EN or UL regulations) is mandatory and influences the design and operation of the equipment. These standards consider various safety factors, such as the toxicity and flammability of refrigerants, to determine acceptable charge limits.

• EN 378 (European Standard): In Europe, the charge limit for R290 in commercial and industrial applications can vary passed on the type of occupancy, equipment location, and room size. Generally, the charge limit is higher for larger, well-ventilated spaces and may exceed the 150 grams specified by IEC 60335-2-40, especially for equipment installed in unoccupied machine rooms or outdoor locations.

• UL 60335-2-89 (United States): In the U.S., the charge limit for flammable refrigerants in certain applications is also typically around 150 grams. However, some applications may allow for higher limits if the equipment is installed in controlled environments, such as industrial applications with restricted access.

Manufacturer Certification: The chiller’s manufacturer will typically provide certification and guidelines indicating the maximum allowable refrigerant charge for their equipment, based on compliance with relevant standards and safety testing. These certifications ensure that the equipment meets all necessary safety requirements and can be operated safely within the specified parameters.

Propane (R290) offers a promising alternative to synthetic refrigerants in recirculating chillers, with notable environmental and energy efficiency benefits. However, its flammability presents a significant safety challenge, requiring careful consideration of factors like room size, ventilation, and regulatory compliance. While transitioning to propane requires new equipment, the adaptability of current designs can facilitate a smoother changeover. As the demand for sustainability and energy-efficient cooling solutions grows, propane’s role in the refrigeration industry is likely to expand, encouraging further innovation and adoption in the future.