www . refrigerationandaircon . co . za RACA Journal I June 2023 39
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Charging equipment : There are different methods of measuring the amount of refrigerant charged into a system :
• By weight , using an accurate digital scale
• To known suction and / or discharge pressures
• To a frost line : this is not very accurate and should be used only for small , fixed orifice systems running at the required temperature
The amount of refrigerant charged into a system affects its performance . If too much or too little refrigerant is charged , the capacity of the system will be lower than expected and / or the power consumption may be higher .
Weighing the refrigerant is the most accurate method and should be used for all refrigerants where possible . Use an electronic scale with an accuracy of ± 1g when charging systems with less than 100g of refrigerant . For greater charge weights less accuracy is acceptable . Electronic scales are safe to use with HC refrigerants , you do not need to make any changes . The amount of refrigerant that one should charge into a system is found on the system ’ s data plate . If you do not know the weight of refrigerant , then charging to the correct suction pressure is the next best method .
Whichever method is used , make sure that if your charging equipment is also used with another refrigerant , for example R134a , you do not contaminate the HC refrigerant . Evacuate or purge equipment such as hoses before using it on a different refrigerant .
Charging to the correct suction pressure : Appliances are often charged with refrigerant while they are running , and the refrigerant is slowly charged in until the correct suction pressure has been reached . This method is not as accurate as charging by weight . Test work has shown that the error in refrigerant amount is ± 15 %. This can significantly reduce the capacity and efficiency of the appliance .
The equipment used for this procedure usually consists of suitable hoses and a gauge manifold . Typically , the suction pressure for R600a will be close to atmospheric pressure for a chilled food appliance and will be lower than atmospheric pressure for a frozen food appliance .
Summing up the procedure for charging HC refrigerants :
• The procedure must be followed for safe and accurate charging .
• The steps are good refrigeration practice .
• All of your tools , instruments and equipment must be suitable for use with HC refrigerants .
Ensure the area is ventilated or work outside : This will ensure that any HC refrigerant which leaks will be safely dispersed . There must be no flames or ignition sources within two to three metres of the charging area . Switches within two to three meters of the charging area should not be used . A dry powder type fire extinguisher must be present in the charging area .
Connecting the charging hose ( s ) and manifold sets : The hoses should be as short as possible to reduce the amount of refrigerant vented ; for example , if there is a problem during charging shorter hoses mean less refrigerant being vented . Connect the hose ( s ) to the charging equipment and system . If there is air in the hoses ( or any other gas that is not HC ) you must remove it . Avoid purging the hoses if possible . If you can , you should evacuate them using your vacuum pump . If you do purge the hoses , do this carefully using refrigerant from the cylinder . Purging is more hazardous when flammable refrigerant is used , so minimise the loss of refrigerant by venting off the air at the connection to the system by purging for one second . This is sufficient time to push air out of the lines .
Charging the HC refrigerant : Accurately weigh in the HC refrigerant . Refrigerant is charged into the process tube of the compressor so any liquid must be evaporated before it enters the compressor . Once charging is complete remove the charging hose ( s ) carefully to minimise the amount of refrigerant lost . Do this by closing the cylinder valve and running the system to draw in as much refrigerant as possible from the
www . refrigerationandaircon . co . za RACA Journal I June 2023 39