Published on 1 - March - 2008
Refrigerants: Leak testing is the key
According to Jane Gartshore of Cool Concerns Ltd, most leaks are not found on commercial refrigeration systems because most engineers are not properly equipped or given the time to leak test effectively
LEAK testing is one of the most important maintenance activities, but to be effective appropriate leak testing equipment must be used; time must be invested in the process; and the leak test schedule must reflect the requirements of the plant.
The previous IoR paper highlighted the importance of the service sector in reducing refrigerant emissions. For example, in 1998 the leakage rate of UK retail systems was estimated to be 14.4%, with significantly higher leak rates in central plant direct expansion systems. The Fluorinated Gas (F Gas) Regulation provides a legal requirement to minimise leakage, and has highlighted the importance of this issue. This paper aims to provide a guide to refrigeration contractors to:
• Summarise the requirements of the F gas Regulation with regard to leak test procedure and leak testers’ qualifications;
• Provide an action plan to help contractors comply with the F Gas Regulation, but more importantly to provide practical information to significantly improve the success rate of routine leak testing. This paper only covers matters associated with leak testing existing systems. The F Gas Regulation covers other issues such as leak tightness of new systems, engineer qualifications for refrigerant handling and fixed leak detection systems.
Leak checking procedure
The flow chart summarises the standard leakage checking requirement as specified in the F Gas Regulation. Leak testing and repair can only be carried out by technicians with an appropriate qualification (see the Action Plan for more information). The frequency of leak testing required by F Gas Regs depends on charge amount:
• Less than 3kg (or 6kg for hermetically- sealed systems) – no requirement
• 3 to 30kg – 1/year
• More than 30kg – 2/year
A fixed leak detection system is required for systems with more than 300kg charge.
It should be noted that frequencies specified in the F Gas Regulation are a minimum requirement – many systems require more frequent leak testing.
Direct leak test methods
The following direct methods of leak detection are permitted in the regulation:
• Hand-held leak detectors with an accuracy of at least 5g/year. The detector should be checked annually
• Fluorescent additives coupled with an ultraviolet lamp
• Leak detection spray/soapy water
Most engineers in the commercial sector prefer to use either leak detection spray (soapy water) or electronic leak detectors. Many electronic detectors in use are not maintained or regularly tested against a calibrated leak source and are therefore not to the accuracy required by the regulation. More importantly, they are not detecting leakage accurately. The fluorescent additive system is a fast and less tedious method of leak detection. It should only be used in systems where approved by the compressor manufacturer – in general, hermetic compressors are not guaranteed if the additive is used. The additive has been found to be ineffective where coalescent oil separators are used. Care must be taken when charging the additive into the system – too much or too little additive is ineffective. If oil is changed in the system more additive should be charged in, although it is difficult to estimate how much is needed.
Indirect methods Indirect methods of leak detection can be used if:
• Leaks from systems develop slowly and are difficult to detect using direct methods; and
• Systems are located in well ventilated areas so refrigerant disperses too quickly for direct methods; and
• The indirect method provides accurate information about refrigerant charge.
Pressure, temperature, compressor current, liquid level or recharge volume can be analysed to identify if refrigerant has leaked. The methods listed in the table below are acceptable under the F Gas Regulation. However, many have significant limitations which reduce their effectiveness at providing a sufficiently early and comprehensive warning of refrigerant loss. These limitations are also listed. It can be seen that, for many systems, indirect methods will not provide an early warning of leakage. The most reliable indirect method is monitoring the liquid level, but this must be coupled with software which takes account of the variations in liquid level which occur with changes in ambient and load. Other indirect methods listed miss leaks or provide a warning after a significant amount of refrigerant has leaked.
Action plan for service and maintenance contractors Leak testing of systems with more than 3kg HFC charge (6kg for hermetically sealed systems) is mandatory under the F Gas Regulation. This regulation has highlighted the need to reduce refrigerant emissions and it provides an incentive to reduce leakage which has been lacking to date. This action plan provides practical advice to contractors so they can meet the requirements of the F Gas regulation but, more importantly, they can reduce leaks from the systems they maintain.
1. Understand your obligations under the F Gas Regulation. Note that current leak detection on many systems is currently inadequate and leakage is unacceptably high. This increases the environmental impact, cost and unreliability of systems. The F Gas Regulation provides a mandatory requirement to check and repair leaks on HFC systems.
2. Determine and record the HFC charge in systems you maintain, and from this prepare the leak test schedule for each system. The leak test regime depends on the system charge (see above). However, many systems would benefit from a more frequent leak test.
3. Identify and record joints in each system which are known to cause leakage. In the longer term this information should be used to inform improved equipment specifications.
4. Prepare a refrigerant log for each HFC system. Appendix 3 of “R22 Phase Out and F Gas Regulations” provides a template for such a log.
5. Check all hand-held leak detectors have a sensitivity of at least 5g/year. They need to be checked every 12 months. Source new leak detectors if necessary.
6. Assess systems for suitability for fluorescent/ultra violet leak detection. This is a successful leak detection method for many systems and it is quick, ensuring more thorough leak detection during maintenance. Charge the additive into those systems for which it is suitable.
7. Ensure technicians carrying out leak testing are qualified to the F Gas standard (required from July 2008). The qualification is due to be finalised by the end of this year and will include the following skills and knowledge:
• Knowledge of units of measure, climate change, global warming potential, the F Gas regulation and potential points of leakage;
• Ability to check a system for leakage using direct and indirect methods;
• Use of gauge sets etc and interpretation of readings;
• Use of an electronic leak detector;
• Ability to check and complete records. A City and Guilds qualification will be available to meet this requirement.
8. Carry out leak testing and repair in accordance with the F Gas Regulation. Leaks found must be repaired and must be re-leak tested within a month. Refrigerant charged and recovered and all leak tests must be recorded. The schedule of leak testing required by the F Gas regulation is the minimum needed for a system – for effective leak reduction, many systems require more frequent leak testing or continual monitoring.
Penalties for non compliance
The UK Government has issued a draft statutory instrument laying out the proposed penalties associated with non compliance with these obligations of the F gas and ODS Regulations. Powers have been proposed for enforcement authorities to serve enforcement and/or prohibition notices, specifying action that must be taken. The proposed Regulations state that a person guilty of an offence under the Regulations is liable, on summary conviction in a Magistrates’ Court, to a fine up to the statutory maximum (up to £5,000) and an unlimited fine on conviction in the Crown Court. The enforcement authority is likely to be the Local Authority.
The F Gas Regulation provides an incentive for reducing leakage and provides a framework for improved leak detection. It highlights the crucial part the maintenance engineer plays in reducing leaks. Compliance with the regulation is not onerous, but most contractors will need to ensure that methods used meet the regulation, in particular with regard to frequency of leak testing, quality of equipment used, knowledge of system charge and record keeping. By July 2008 a qualification will be in place for leak-test technicians which will be a mandatory requirement. The requirements of the regulation should be seen as a minimum standard – many systems require more rigorous leak testing to significantly reduce refrigerant loss.
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