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By Grant Laidlaw

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.

Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy (ACRA) in Edenvale. He holds a Bachelor of Business Administration and an associate degree in educational administration. He has a National TechnicalDiploma and completed an apprenticeship with Transnet. He has dual-trades status: refrigeration and electrical. He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018. Currently he is the SAIRAC national treasurer.

Hi Stanley. At the moment in South Africa the highest percentage of equipment using hydrocarbon refrigerants would be the domestic and light commercial sectors. However, the impact of the Montreal Protocol and in particular the Kigali Amendment will most certainly see an increase in the quantity and scope of equipment using hydrocarbon refrigerants. This is especially true of R290. In the overseas markets the use of R290 extends into and from the unitary air conditioning market right up to and including large capacity indirect industrial chillers.

Stanley, the release of natural refrigerants including R290 is virtually harmless to the environment, but we must consider all of our options. In addition, while venting is permissible, we have to consider the health and safety aspects. As you may be aware when dealing with hydrocarbons (R290, R66a) flammability and asphyxiation are hazards which must be considered.

All hydrocarbon refrigerants are highly flammable and even explosive when mixed with air. The flammability issue is manageable if certain measures are in place. Specifically for refrigerant removal, certain safety precautions have to be followed. Refrigerant must be recovered or vented from refrigeration or air conditioning systems prior to working on the refrigerant circuit. Please note that we are exclusively dealing with hydrocarbon refrigerants and not HCFC or HFC refrigerants.

It might also be necessary to remove refrigerant remains from cylinders. Recovered hydrocarbon refrigerant can be collected in a recovery cylinder, vented or burned in a controlled manner.

With regards to hydrocarbon refrigerant, venting should only be carried out as an alternative to recovery if the charge size is smaller than 500g. This is permissible due to the fact that HC refrigerants have no Ozone Depletion Potential and negligible Global Warming Potential. Larger quantities should be recovered.

Before venting a system, it is necessary to ensure that legislation addressing safety of hazardous substances is satisfied; therefore venting must be done in a safe manner.

Venting of hydrocarbon substances:

• A hose (vent Line) should be connected to a gauge manifold set and the point on the system from which the refrigerant will be vented
• The vent line must be of sufficient length and diameter such that it will extend to at least 3m beyond the outside of the building
• There should be no ignition sources within a minimum distance of 2.5m from the hose end
• The hose should be made of material that is compatible for use with HC refrigerants and oil
• The hose end should be raised approximately 1m above ground level and so that the discharge is pointed in an upwards direction to assist with dilution
• Should there be an emission of refrigerant oil, it should be collected and disposed of in the correct manner
• The hose should be checked to ensure that there are no holes or kinks

Precautions to be taken:

• Venting to the inside of a building is not permissible under any circumstances
• Venting must not be to a public area, or where people are unaware of the procedure taking place
• Venting should only take place if the refrigerant cannot get blown back into any adjacent buildings, and if it cannot migrate to a location below ground level (enter into drains etc)
• A flammable gas warning sign must be positioned close to the hose discharge

Tools:

• Manifold gauge set with calibration for the refrigerant in use
• Set of refrigerant transfer hoses with plastic hose of appropriate length for use as vent line (approximately 15m)
• One set of access valves in order to minimise refrigerant release during equipment connection at appliances/system service ports (if required)
• Flammable refrigerant gas detector depending on risk assessment
• Floor standing fan to disperse any refrigerant leakage
• PPE according to risk assessment
• Safety area warning signs

Preparation for venting:

• Inform owner, supervisor and obtain permit for work (if required)
• Wear PPE as required
• Place the warning signs within the work area
• Switch off the refrigerating system
• Switch on the leak detector (leak finding device) at fresh air outside condition and place on the floor area near the equipment
• Use the correct refrigerant manifold and connect refrigerant transfer hoses as required
• Use a small floor fan to vent the area around the equipment and disperse and accidental leakage to below the refrigerants lower flammability limit

Venting process:

• Use a floor fan and connect the manifold gauges
• Check that all temporary refrigerant hose connections are tightened (all connections are Temporary Flammable Zones)
• The gauges show the standing pressure in the system
• If the system is pressurised, open valves on the manifold gauge set to begin venting
• Set to a low flow rate through the vent-line to ensure the refrigerant is well diluted on exit
• Check flow of hydrocarbon refrigerant (pressure indications, sight glass on manifold, vent-line outlet)

Continue venting refrigerant until pressure gauges indicate 0 kPa (atmospheric pressure). Do not hurry, allow the refrigerant to flow out of the refrigerating appliance completely. Remember that refrigerant is absorbed into the compressor oil and the system still contains refrigerant at atmospheric pressure.

Once venting is complete:

• Close all valves
• Evacuate the system using a suitable vacuum pump for use with flammable refrigerants

Once the complete evacuation process is completed, purge with nitrogen (allow nitrogen to flow through system). If purging with nitrogen is not possible, the system should be pressurised with nitrogen and the evacuation procedure repeated, to ensure that there is minimal HC refrigerant remaining inside the system. Mark the system ‘Empty’.

Stanley, moving on to flammable refrigerant recovery. For systems with refrigerant charges larger than 500g, in most circumstances it is recommended to recover the refrigerant, as opposed to venting.

For this you will need recovery cylinders which are specially designed for the extraction of refrigerants (and oil) from refrigerating systems. Recovery cylinders should have a dual-port valve for liquified and vapour refrigerant. They are constructed according to international and local standards. Note: These recovery cylinders are typically not recommended for the use with R-32 refrigerant.

Flame proof vacuum pump suitable for use with flammable refrigerants. Image courtesy Testo

Do not exceed the maximum charging capacity of the cylinder. When a container is filled with refrigerant, the maximum charge should always be observed by using a calibrated weighting scale, taking into account that possible refrigerant mixtures have a lower density than pure refrigerant. The usable container capacity should therefore be reduced. It should be noted that the density of R290 at 50°C is 0.449 kg/dm³ and the density of R600a at 50°C is 0.517 kg/dm³.

The charging capacity is a result of the internal volume of the container and the liquid density of the refrigerant at a reference temperature (70% liquid by volume at 50°C). Do not exceed the allowable pressure of the container, even temporarily, during any operation. Special valves may be fitted to the refrigerant container to avoid the possibility of over-filling. Container filling to be carried out according to national regulations. Do not mix different refrigerants, refrigerant should not be placed in a container that contains a different or an unknown refrigerant. An unknown refrigerant already in a container should not be vented to the atmosphere but reclaimed and disposed of in the correct manner.

Refrigerant recovery cylinders that are over-filled exceeding the allowable charge amount may vent refrigerant through their safety valves. Large quantities of vented hydrocarbon refrigerant into for example a vehicle represents a major safety hazard. In addition severely overfilled cylinders can explode with catastrophic consequences.

Refrigerant charging into cylinders must be monitored with the use of calibrated charging scales and all processes involving temporary connections and systems under pressure should never be left unattended.

Warning of non-condensable gases (typically nitrogen and air): In the case of non-condensable gases entering HCFC and HFC cylinders, although undesirable, could more easily be dealt with. In the case of flammable refrigerants, it is of fundamental importance to avoid transfer of non-condensable gases into the recovery cylinder. Air has to be especially avoided as it contains oxygen. Air can easily be introduced into the cylinders or systems by not following the correct maintenance and repair procedures.

Air can enter the system by different means. It may be drawn into a system through a low side leak if the suction pressure drops below atmospheric pressure. Air may be already in the refrigerant circuit of the system to be serviced, or it is introduced into the recovery cylinder during the refrigerant recovery and transfer process. The oxygen in air will create a critical combustible mixture at higher pressures with refrigerants.

Before refrigerant recovery, all transfer hoses should be purged or evacuated to remove air or other non condensibles. During flammable refrigerant recovery, do not run the refrigerant circuit into a vacuum! Do not activate the low-pressure override function of the recovery unit. Stop the recovery process at 0 bar to prevent accidental introduction of air. Once the refrigerant recovery process of flammable refrigerant is completed the system should be purged with nitrogen.

Whenever possible and if single substances are used, check the filled recovery cylinder for the existence of non-condensibles by doing a temperature/pressure comparison!

This is done by placing the cylinder in a stable environment for 10 hours or overnight. Measuring temperature of the bottom quarter of the refrigerant cylinder. Place a manifold gauge set on the vapour service valve on the cylinder, open the value and record the pressure. The pressure should correspond with temperature on the pressure temperature chart for the specific refrigerant.

Should the pressure reading be higher than what is indicated there are non-condensibles present in the cylinder. Following all the safety rules applicable to venting flamable refrigerants, vent the non condensibles out of the cylinder until the pressure corresponds with the indicated temperature indicated on the chart.

Marking of recovery cylinders with flammable refrigerants. The cylinder containing recovered refrigerant should be marked to note any special conditions, For example ‘HC R-290– Recovered’. A red band on the shoulder or top of the container should designate flammable compounds, or mixtures that could become flammable in the event of a leak.

Stanley, I hope that this helps with your understanding around venting flamable refrigerants. I will continue with the recovery process in the next edition.

References:

1. ACRA
2. The Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH,
3. Testo

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