The Use Of Flammable Refrigerants

Regular Technicals Support

By: Grant Laidlaw

Welcome to the Solutions page

Many people ask for assistance in the understanding of theoretical and practical aspects of the industry. I will endeavour to enlighten. We are going back to basics as I have questions coming in that indicate that the basic understanding necessary to work in industry is not in place.

Clement asks: Hi Grant, I see that in the air conditioning space we have some technicians, who when working on R32 units they remove the R32 and use R410a. They do not know how to deal with the safety aspects of R32. Can you please discuss the use of flammable refrigerants.

Hi Clement, thanks, replacing R32 with R410a is not advisable. Let us look into flammable refrigerants in more detail as their usage is definitely on the increase.

Working with flammable refrigerant and cylinders requires strict safety procedures due to their high flammability. The primary danger is fire or explosion if the gas leaks and finds an ignition source. Proper training and adherence to safety protocols are critical for anyone handling these materials.

General Safety Guidelines

Use the right equipment:

All tools and equipment, including recovery machines, vacuum pumps, leak detectors, and charging scales, must be rated for use with flammable refrigerants and not create a spark. Remember that single phase electric motors may use brushes which create arcing when in use.

Control the work area:

Establish a 2 to 3 meter hazard zone around the system, post signs and remove all ignition sources.

Eliminate ignition sources:

Remove or turn off all potential ignition sources, such as open flames, sparking electrical components, and mobile phone usage.

Dealing with ignition sources:

There should be no sources of ignition as part of the refrigerating system or equipment.

Precautions should be taken to avoid the possibility of direct sources of ignition from exposed electrical contacts. Electrical items that have the potential to produce electrical sparks during normal operation should receive particular attention to eliminate them as potential sources of ignition. The following methods can be applied:

• Insulate terminals
• Locate within an approved enclosure
• Replace with solid state type component
• Replace with sealed type component
• Locate externally

Adequate precaution is achieved providing the items mentioned above are used within the refrigeration system.

Ensure adequate ventilation:

Always work in a well-ventilated area, preferably outdoors. flamable refrigerants are heavier than air and can accumulate in low areas posing an asphyxiation and flammability risk. Use an extraction system in workshops and / or a fan to disperse any refrigerant release.

Fire extinguisher:

Ensure that a suitable fire extinguisher is available.

Use personal protective equipment (PPE):

Wear gloves, safety goggles, and full-coverage clothing to prevent frostbite from contact with liquid refrigerant

The following types of flammable refrigerants are in use:

R290 Propane, R600a Isobutane, R1270 Propylene and the A2L refrigerants R32 and 1234yf.

A number of other hydrocarbons, such as blends containing ethane, propane or butane, are also used as refrigerants.

Efficiency

Hydrocarbons have excellent thermodynamic properties, and in this respect they are as good as or better than HCF or HCFC refrigerants in most applications.

Flammability limits

Hydrocarbons are highly flammable and must be handled with care. If they are used responsibly, hydrocarbons can be employed in a variety of refrigeration and air conditioning applications.

In order to ensure safety, applications are governed by various international, regional and national standards and regulations.

Flammable refrigerants can only pose an explosion risk if the concentration is between the lower and upper flammability limits.

When following the safety standards the concentration of leaked refrigerant will not get above the LFL where ignition sources can ignite it. The necessary safety precautions and system design depend on the refrigerant charge.

Most hydrocarbons are non-toxic, with the main safety risk coming from their flammability, although gaseous hydrocarbons will displace air due to a higher density.

Environmental Impact

Flammable refrigerants belong to the group of natural refrigerants and have zero ODP and negligible GWP. As a rule, hydrocarbons are by-products from the petrochemical industry.

Pressure and Temperature

The refrigeration properties of hydrocarbons, such as pressures, pressure ratios and discharge temperatures, are quite similar to those of HCFCs or HFCs in many respects.

Chemical Properties

The most commonly used hydrocarbons (propane and isobutane) are compatible with standard oils and materials used with HFCs. One exception is propene (propylene), which is not compatible with neoprene. Consequently, special O-rings must be used with this refrigerant.

Economic Aspects

The relative cost of a system using hydrocarbons largely depends on the application. In domestic and light commercial applications, the cost of the system is similar to that of systems with HFCs.

Typical applications for hydrocarbons are:

• Domestic refrigerators and freezers
• Bottle coolers
• Ice cream freezers and commercial freezers
• Commercial refrigerators
• Beverage dispensers
• Heat pumps
• Supermarket refrigeration
• Unitary air conditioners
• Chillers (R290)

Lubricants

Flammable refrigerants possess full chemical compatibility with nearly all lubricants commonly used within refrigeration systems. Good miscibility is maintained with most lubricants under all operating conditions.

Due to the particularly good solubility with mineral oils, it may be necessary to use a lubricant with lower solubility or increased viscosity to compensate for possible thinning under situations where high solubility could occur. Suppliers should be consulted for properties of oil/refrigerant combinations.

Lubricants containing silicone or silicate (often used as anti-foaming additives) are not compatible with hydrocarbon refrigerants and should not be used.

Materials

Virtually all common elastomer and plastic refrigeration materials used as ‘O’ rings, valve seats, seals and gaskets are compatible with hydrocarbon refrigerants.

These include Neoprenes, Nitrile rubbers, HNBR, PTFE and Nylon. Materials that are not compatible and should not be used in hydrocarbon refrigeration systems are EPDM, natural rubbers and silicone rubbers.

Whilst testing has been conducted on a number of selected materials with hydrocarbons it should be noted that there are numerous different grades available in the market and for this reason compatibility should be checked with the manufacturer or supplier of the component.

System Components

Typically system components used for fluorocarbon refrigerants do not differ significantly when using flammable refrigerants. Component suppliers should be consulted regarding other in-line components such as pressure regulators, solenoid valves, etc.

• Evaporators and Condensers: Evaporators and condensers using hydrocarbons tend to be virtually the same design and size as those used for conventional fluorocarbon refrigerants that operate at similar pressures. Heat transfer coefficients tend to be higher for most hydrocarbons but this does not significantly affect heat exchanger dimensions. All common types of heat exchangers are suitable for use with hydrocarbon based refrigerants including:

• Compressors: Most compressor types are suitable for use with hydrocarbon refrigerants and compressor suppliers should be consulted for application and selection. Using a compressor with flammable refrigerants without the supplier’s approval may invalidate the warranty. In order to secure satisfactory performance, long life, and to protect the compressor against overload, certain design criteria should be observed. Compressor application notes and data should always be consulted when designing a system. Ensure compressors are clearly labelled to indicate that hydrocarbon refrigerants are being used in the system. The use of crankcase heaters should be considered to avoid excessive oil solubility.

• Refrigerant Control Devices: All expansion device types are suitable for use with hydrocarbon-based refrigerants and component suppliers should be consulted for application and selection. Design and selection criteria are the same as those for conventional fluorinated refrigerants. Capillary tube length is specific to each refrigerant. Computer programmes and tables are available for determining capillary tube size and length, although trial and error is generally the preferred route. Thermostatic Expansion Valves (TEVs) for hydrocarbons are available from control suppliers. Alternatively TEVs for other refrigerants that operate with similar pressure-temperature relationships can be used. Electronic Expansion Valves (EEV) may also be used. EEV’s used in hydrocarbon systems must conform to the requirements of electrical components.

• Desiccants: Desiccants are used within filter dryers. Most commonly used desiccants are compatible with flammable refrigerants.

• Pipe Size Selection: When selecting refrigerant line sizes, specific flammable refrigerant pipe sizing literature should be used. Despite most flammable refrigerants having similar operating pressures to the “equivalent” fluorocarbon refrigerants, thermodynamic and transport properties can differ significantly, thus data for other refrigerants will not be directly applicable. Refrigerant suppliers should provide the appropriate pipe size selection data.

Safe System Design and Construction

All hydrocarbon refrigerants are highly flammable but non-toxic. There are many other safety requirements that should be considered in the design and construction of all refrigerating and air conditioning installations, regardless of the flammability of the refrigerant used.

General safety standards and codes of practice should be consulted for this additional information.

Allowable Refrigerant Charge

The limiting factor associated with the use of hydrocarbon refrigerants is the refrigerant charge size, the occupancy category and the room size.

Clement, I will go into further aspects including the refrigerant charge size, the occupancy category and the room size in the next issue.

Flammable refrigerants are being used in more and more applications. It is very important to understand the use of these refrigerants.

Grant Laidlaw

grant@acra.co.za

REFERENCES:

ACRA

SANS 10147