Refrigerant recovery allows work to be carried out in the refrigeration circuit without releasing a quantity of refrigerant into the environment. Most refrigerants are strong greenhouse gases and their discharge into the environment should be kept to a minimum. In addition, the European F-gas Regulation requires the recovery of refrigerant when repair work or refrigeration decommissioning is required.

Secur​ity

For any work we perform, safety must always be taken into account. For this reason:

• We always use personal protective equipment, goggles, gloves and safety equipment before any work
• We take care of the best possible ventilation of the space
• Always weigh and pay attention to the weight of the bottle in which we make recovery so as not to exceed the maximum filling weight
• The bottle in which we are recovering should be suitable for the refrigerant we are recovering and should not have exceeded its expiration date (recovery bottles should be checked and re-certified every 5 years)
• We turn the safety valve of the bottle away from those who work in the area
• Different refrigerants should not be mixed in the same recovery bottle
• The bottle must state the refrigerant recovered and the note that it is recovered refrigerant
• The pressure in the bottle should not exceed the pressure allowed by the bottle

Maximum amount of filling

If the recovery bottle contains the maximum filling weight for the refrigerant we recover, this value should be used for the maximum filling amount. Otherwise, based on the European regulation EN378, the maximum amount of filling should be calculated. The refrigerant recovered is mixed with a quantity of lubricant resulting in a lower density than the pure refrigerant. For this reason the filling volume of the bottle must be smaller than its capacity in pure refrigerant. According to the regulation, the maximum filling quantity is calculated in 2 ways and the lower of the two values ​​is valid:

 1st Way.  80% of the maximum amount of clean refrigerant in the bottle

2nd Way. 70% of the bottle volume

For example in a bottle stating that the amount of pure refrigerant R134a that it may contain is 15 kg and its volume is 15.3 lt then:

1st Way. 0,8 x 15 = 12kg

2nd Way. 0,7 x15,3 lt = 10,71 lt. The density of R134a at 25 ° C is 1,206kg / lt so the maximum amount of filling is 10.71 x 1.206 = 12.92 kg

As shown, way 1 calculates a smaller quantity so it determines the maximum filling amount of the bottle in which we perform the recovery.
In the case of hydrocarbon recovery should not exceed 45% of the maximum filling.

Equipment

The necessary equipment for the completion of the refrigerant recovery work consists of:

1. Recovery machine suitable for the refrigerant to be recovered (Figure 1)
2. Scale
3. Hoses and fittings
4. Hose removal tool
5. Filter
6. Recovery bottle
7. Means of personal protection

Figure 1. Recovery Machine

Refrigerant recovery techiques

The most common way of recovery is to use a recovery machine which removes liquid and gaseous refrigerant from the system and transports it to a flask. However there are several connection methods that can increase the recovery flow (reducing time) and prevent the pressure in the bottle from increasing.

The most common technique (Figure 3) is to connect the manometers to the circuit and the recovery machine with ¼ in hoses and then connect the recovery machine to the bottle again with ¼ in hoses. A filter should always be fitted at the inlet of the recovery machine to protect it. With this connection we can recover both liquid and gaseous refrigerant from the circuit.

Figure 2. Valve core removal tool.

To achieve faster recovery you should:

1. Remove the cores from the valves of the system to which we connect the hoses for recovery (Figure 2). These cores block about 95% of the flow from the valve.
2. Remove the hose fittings that push the valve as they block about 50% of the hose.
3. Even if the service valves of the circuit are ¼ in. 3 / 8in hoses should be used both in the connection to the circuit and in the connection of the recovery machine to the cylinder. The cross section of the hoses has a great effect on the recovery speed.
4. The hoses should be as short as possible so that the flow is not slowed down and a large amount of refrigerant is not trapped in them.
5. The hose from the recovery machine to the cylinder should be connected to the gas valve of the cylinder. In this way the refrigerant does not need to pass through the thin tube that the bottle has in the liquid valve and would restrict the flow.
6. If a small bottle is used, the bottle should be turned upside down while the liquid refrigerant is being recovered and placed in its normal position when all of the liquid refrigerant has been recovered and gas is now being recovered. This limits the increase in cylinder pressure as much as possible. As the recovery rate is much higher as liquid refrigerant is recovered, tracking the scales makes it easy to understand when the recovery engine starts to recover gas refrigerant.

Figure 3. Standard hose connection for refrigerant recovery.

During recovery the temperature of the recovery bottle rises. The reason that the temperature in the cylinder rises is the entry of gaseous refrigerant into it. To condense the gaseous refrigerant, the cylinder must dissipate heat to the environment, causing the temperature of the cylinder to rise. There are two ways to limit the increase in bottle temperature.

1. Insert a mechanical subcooling system between the recovery machine and the recovery bottle. Essentially we add a condensing unit which cools the refrigerant before it reaches the bottle, ensuring that it will go to the bottle in a liquid state. However, this increases the complexity and also increases the hose measures used, thus trapping a larger amount of refrigerant.
2. Cool the bottle with water, ice or wet cloths. In this way we help the bottle to eliminate the condensing heat of the gaseous refrigerant.

Another way to reduce the recovery time is to connect the hoses differently. Slightly modifying the previous connection (figure 4), add a hose from the gas valve of the cylinder to the gas line of the circuit. The pressure difference allows the bottle gas refrigerant to return to the circuit and then be recovered by the recovery machine, helping to cool the bottle.

Figure 4. Hose connection technique for faster refrigerant recovery

Finally, a different way of connecting is the push-pull method (Figure 5). In this method the recovery machine takes gas refrigerant from the cylinder and inserts it into the compressed circuit to "push" the liquid refrigerant directly into the cylinder. Once the entire amount of liquid refrigerant has been recovered the recovery should continue with the previous connection. This process is used only in refrigeration circuits with a large amount of refrigerant.

Figure 5. Connection of hoses for refrigerant recovery with the Push-Pull method.

Summary

Refrigerant recovery is a time consuming process but it is necessary and should in no way be replaced by the discharge of coolant into the environment. However, there are several techniques that can significantly reduce the recovery time depending on the application. Recovery must be carried out by qualified personnel with a refrigerant license and refrigerant management certification in accordance with the European F-gas Regulation.

Bibliography
[1] European regulation ΕΝ378
[2] AshraeHandbook – Refrigeration
[3] Promax minimax manual