By Grant Laidlaw
Safe working practices of this refrigerant start with the legal requirement of being registered to do so, and further include tools and considerations.
Johann asks: Grant, there is talk on hydro carbon refrigerants, the flammability aspect and required training, but what of R32? Surely some training is required as at the end of the day? R32 does fall into the A2L category. Can you give some indication as to safe working practice for R32?
Johann, we had a look at R32 in the previous issue, and found that R32 is mildly flammable and precautions do need to be taken. By law, all persons working with refrigerants in South Africa need training and need to be registered to use R32 – and/or any other refrigerant for that matter.
To install a system that utilises R32 refrigerant, dedicated tools and piping that have been manufactured specifically for R32(R410A) should be used. The pressure of R32 refrigerant is approximately 1.6 times higher than R22. Failure to use dedicated piping or incorrect installation procedures can cause ruptures with consequent injuries.
Use a vacuum pump and refrigerant recovery equipment suitable for use with flammable refrigerants.
Electronic leak detectors can be used to detect flammable refrigerants, calibrated in a refrigerant-free area.
Gauge manifold sets specific to R32 should be used. You should not use your conventional (R22) manifold gauges as the system pressures are too high for these gauges. In addition, we do not want to contaminate the refrigerants and oils in the systems.
In order to avoid this, the diameter of each port has been changed to prevent the use of R22 gauge sets on R32 systems. The hose sizes and materials are therefore specific to R32. The R32 gauges typically can read up to 5.3MPa for a high pressure gauge and 3.8MPa for a low pressure gauge.
Understanding the need to minimise the risk when a flammable gas or vapour is present while the work is being performed is crucial. You should always conduct a risk assessment prior to undertaking any work on a system.
Some of the practical considerations include:
- Ensuring that technicians are aware of a potentially flammable atmospheres.
- Checking for refrigerant leaks with an appropriate refrigerant detector.
- Ensuring that there are no ignition sources, for example: open flames or arcing on electrical motors (brushes). These ignition sources should be kept sufficiently far away from the site of installation and repairing during which flammable refrigerant can be released to the surrounding space.
- Ensure that the area is in the open or that it is adequately ventilated before working on the refrigeration circuit. The ventilation should safely disperse any released refrigerant externally into the atmosphere.
- Where electrical components are being changed, they must be to the correct specification for use with flammable refrigerants.
- When capacitors are discharged: this must be done in a safe manner to avoid the possibility of arcing.
- There must be no exposed electrical components and wiring whilst charging, recovering or purging the system and there must be adequate earthing.
- If it is necessary to have an electrical supply to the system during servicing, continuous leak detection is recommended.
- If a leak is suspected, all naked flames should be removed/extinguished.
- If a refrigerant leak is found which requires brazing, all of the refrigerant must be recovered from the system, or when possible isolated (by means of shut off valves) in a part of the system remote from the leak.
- Nitrogen should be purged through the system both before and during the brazing process.
- When transferring refrigerant into cylinders, ensure that only the appropriate refrigerant recovery cylinders are used.
- All cylinders to be used are designated for recovered refrigerant and labelled for that refrigerant. Cylinders must be equipped with a pressure relief valve. Empty recovery cylinders should be evacuated before use. Calibrated weighing scales should be used to avoid overfilling of recovery cylinders. It is very important not to mix refrigerants in recovery machines and cylinders.
- If compressors or compressor oils are to be removed, ensure that they have been evacuated to an acceptable level to make certain that flammable refrigerant does not remain within the lubricant.
When breaking into the refrigerant circuit the following procedure represents good practice:
- Removal of refrigerant from the system.
- Purging the system with nitrogen.
- Evacuate, ensuring that the refrigerant is removed from the oil ensuring that the outlet of the vacuum pump is not close to any ignition sources and that there is ventilation available.
- Perform a second purge of the system with nitrogen.
- It is now safe to work on the system including brazing.
Purging can be achieved by breaking the vacuum in the system with nitrogen and continuing to fill until the working pressure is achieved, then venting to atmosphere, and finally pulling down to a vacuum.
When installation/repair is complete a follow up leak test should be carried out prior to leaving the site.
Given the increased pressures of R32 over R22 it is necessary to use seamless copper pipes suitable for R32/R410a. Do not use copper pipes which have collapsed, deformed or damaged areas. Never use copper pipes with a wall thickness less than 0.8mm.
Thanks for the question Johann, in terms of refrigerants, we are experiencing rapid, global change and need to ensure our knowledge, procedures and equipment are keeping abreast with changing technology. Flammable refrigerants are, without doubt, here to stay.
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