By Grant LaidlawBy Grant Laidlaw
Many people ask for assistance in the understanding of theoretical and practical aspects of the industry. I will endeavour to enlighten.
|Stewart asks: Grant, in our sector we are moving away from R134a and see the usage of HFOs on the increase, in particular R1234YF. Any advice on the usage would be most helpful, and do we need a safe handling license for R1234YF? Is R1234YF compatible with existing R134a systems?|
Hi Stewart, yes, I am aware of Hydrofluoroolefins, or in short HFOs, being used in the market. This is an acronym that is familiar to many of us. R1234YF, R1234ze(E) are few examples of HFOs. They are used in a number of applications today, predominantly in the automotive sector. These are relatively new in the air conditioning sector, appearing around a decade ago.
What are the HFOs?
Having said that, HFOs are nothing new to the chemistry industry. Much like traditional hydrofluorocarbons (HFCs), they are composed from hydrogen, fluorine and carbon. The only difference is that they are unsaturated, meaning that they have at least one double bond. Such molecules are named olefins or alkenes. The HFO label has become the most used name to refer to refrigerants with carbon-carbon double bonds.
The presence of the carbon-carbon double bond is not unique for HFOs as there are other unsaturated compounds to be found, as for example unsaturated hydrocarbons (for example propene). In fact, HFO-1234YF is a propene molecule that has been halogenated.
Structural formula of HFO-1234YF
HFOs are relatively stable compounds but are more reactive than HFCs due to the reactivity of the carbon-carbon bond. This also reduces their global warming potential (GWP) and thus they became favourable refrigerants in the light of increasing concerns on climate change.
The interest in HFOs as potential refrigerants arose with the adoption of European directives on mobile air-conditioning systems that focussed on reducing emissions of the fluorinated greenhouse gases (GHG). The fluorinated propene isomer R1234YF has thus become the alternative to R134a.
Having said that there are automotive manufacturers who have begun including R744 (CO2) systems to their product line-up. Looking at R1234YF, we find that unlike R134a, R1234YF refrigerant has a very low effect on global warming. This feature is common for HFOs. This is mainly due to HFOs relatively short lifespan in the atmosphere which is only a few weeks for many HFOs. The latest figures suggest the R1234YFs GWP is less than 1.
The benefits of HFOs on the environmental side are partly outweighed by the concerns on their safety.
There are two main safety issues that are related to HFO’s: flammability and their potential to form dangerous acids:
- A number of HFOs, including HFO-1234YF, HFO-1234ze, are flammable.
- HFOs are easily decomposable at high temperatures and form hydrogen fluoride – a gas that is highly soluble in water and that easily forms acid that can cause skin, eye and throat irritation and could lead to death. This becomes an issue should a vehicle be involved in an accident. R1234YF then poses an additional danger to both the vehicles occupants and rescue personnel.
It is obvious that flammable refrigerants have greater probability to be affected by high temperatures and therefore pose greater risk of formation of dangerous substances.
Applications of HFOs
HFOs are a range of synthetic refrigerants that promise to be a part of solution to the environmental problems. They are found in a number of applications. In refrigeration and heat pump technology HFO-1234YF has been chosen to replace R134a in systems; HFO-1234ze and HFO-1233zd are used in chillers. In the automotive sector R1234YF is commonly used.
The application of new HFOs are further extended when they are used as a component for lowering GWP in refrigerant mixtures. When one considers that the industry is in a state of flux with ongoing investigations in regard to the safe use of HFOs and considering the previous generations of synthetic refrigerants, it is still too early to tell whether HFOs represent the long-term solution.
Stewart, you specifically asked about R1234YF, so let us look at this refrigerant.
R1234YF is an HFO refrigerant. HFO refrigerants are composed of hydrogen, fluorine and carbon atoms, but contain at least one double bond between the carbon atoms. Due to its composition, R1234YF does not damage the ozone layer and has minimal global warming impact. R1234YF has similar operating pressures to R134a.
Main characteristics of R1234YF:
- Low toxicity
- Low GWP; GWP = <1
- Zero ozone-depleting potential
- Class A2L Refrigerant – Lower flammability
Stewart, let us now look at this in context and compare the characteristics of R1234YF to R134a.
As you can see, R1234YF compares very well with R134a. The real difference lies in the flammability and acid forming characteristics of R1234YF. This of course means one should handle R1234YF with care.
Equipment needed to handle R1234YF
As when dealing with any flammable refrigerant including hydrocarbons R290 and R600a and HFOs, the general requirement for tools is that they do not create an ignition source and are used in an environment that has no ignition source and has adequate ventilation. This is with particular reference to power tools and single-phase switch gear (equipment on-off switches, light switches and plug points). Particular precautions apply to the use of open flames (brazing equipment).
Figure 1: Structural formula of HFO-1234yf.
Equipment requirements for R1234YF
For automotive applications a unique vehicle quick release fitting is used.
- A R1234YF calibrated gauge set with dedicated R1234YF couplers. Standards have been developed for hoses and couplings.
- Red and blue service hoses, the fittings are 12mm O Ring fittings male with a hexagon nut.
- Yellow service hose ½” LH thread (an adaptor is available to fit a universal vacuum pump).
- Manifold gauge sets designed to take the male fittings of the hose set and are calibrated to read R1234YF temperatures.
- Electronic refrigerant leak detector (A2L compliant).
- Vacuum pump (A2L compliant).
- Recovery/reclamation equipment (A2L compliant). Although it is not mandatory to recover R1234YF, it is still good environmental practice and, due to the cost of this refrigerant, it would be advisable to do so. Having said that, recovery machines that meet these criteria are difficult to obtain in South Africa at the moment.
Dedicated cylinders for R1234YF have a left-hand valve thread and require a suitable adaptor to connect to the gauge set charge hose.
Stewart you asked, “is R1234YF compatible with existing R134a systems?” The short answer is no, R1234YF system refrigerant circuit is accessed using service couplers that are a different size to those of a R134a system. The service coupler hose connection also has a left-hand thread that requires a matching hose for connection. Hence the need for an R1234YF gauge set.
R1234YF is classified as an A2L mildly flammable refrigerant and requires the use of equipment designed for use with such a refrigerant.
The exception is an electronic leak detector. Several manufacturers produce detectors that are suited to both refrigerants. Also, R134a systems were not designed to operate using a flammable refrigerant. The standards lay down specific requirements for system design. For example, the R1234YF evaporator is significantly stronger than the one you would commonly find in an R134a system.
Can a R134a system be converted to R1234YF? Aside from the safety aspects, although the two refrigerants have similar thermodynamic properties, they are not the same. Therefore, compressor damage or system performance limitations may be found when attempting to convert an R134a system to R1234YF.
Do I need a SARACCA Authorisation and Licence to handle R1234YF?
Yes, licence is required. It is a legal requirement that any person working with a refrigerant that is utilised in a system with pressures exceeding 50kPa must be an authorised person in procession of a valid safe handling licence in the correct category.
Safety issues to be aware of when handling R1234YF
R1234YF is classified as A2L mildly flammable. Technicians need to take the relevant safety measures for the correct transport, storage and handling of a flammable gas. This would include, but is not limited to, ensuring no open flames (including smoking) near the system. It is also worth noting that highly toxic / acidic substances are created when this gas is burnt.
Suitable personal protective equipment (PPE) is to be worn when handling this refrigerant. Suitable training in flammable refrigerants is mandatory as per SAQCC authorised persons prior to working on systems containing flammable refrigerants.
Safety checks to the work area:
Prior to beginning work on systems containing any flammable refrigerants, safety checks are necessary to ensure that the risk of ignition is minimised. For repair to the refrigerating system prior to conducting work on the system, the following precautions should be complied with:
- Work shall be undertaken under a controlled procedure to minimise the risk of a flammable gas or vapour being present while the work is being performed.
- All staff and others working in the local area should be instructed as to the nature of work being carried out. Working in confined spaces must be avoided. The area around the workspace is to be sectioned off. Ensure that the conditions within the area have been made safe by control of flammable material.
- The area should be checked with an appropriate refrigerant detector prior to and during work to ensure the technician is aware of potentially flammable atmospheres. Ensure that the leak detection equipment being used is suitable for use with flammable refrigerants, i.e. non-sparking, adequately sealed or intrinsically safe.
- Appropriate fire extinguishing equipment shall be available to hand. Have a dry powder or CO2 fire extinguisher adjacent to the charging area. A first aid box should be evident in the vicinity.
- No person carrying out work in relation to a refrigeration system which involves exposing any pipe work which contains or has contained flammable refrigerant shall use any sources of ignition in such a manner that it may lead to the risk of fire or explosion. All possible ignition sources, including cigarette smoking, should be sufficiently far away from the site of installation, repairing, removing and disposal during which flammable refrigerant can possibly be released to surrounding space. Prior to work taking place, the area around the equipment is to be surveyed to establish any flammable hazards or ignition risks. Display ‘No Smoking’ signs.
- Ensure that the area is in the open or that it is adequately ventilated before breaking into the system or conducting any work. A degree of ventilation should continue during the period that the work is carried out. The ventilation system should safely disperse any released refrigerant.
Stewart, this sums up the basics of HFOs and in particular R1234YF. All I can say is: Interesting times we live in.
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