INSTRUMENTATION & LEAK DETECTION
Can chillers and heat pumps tell us when they're leaking?
By Klas Berglöf head of research and development and founder of ClimaCheck.
E
veryone in our industry has felt the pressure of reducing refrigerant leaks to reduce emission of F-gases – and
with the increasing use of flammable or toxic refrigerants there is even more pressure to know that there are no leaks. Often neglected in the discussion of leak
avoidance is that energy efficiency is affected by leaks and that the indirect contributions from increased energy consumption in most cases are much higher than that of the leaked refrigerant itself. It is also clear that refrigerant will leak in spite of regular leak checks being carried out. Running on a low charge will also cause additional stress on the equipment and eventually result in that system tripping from low suction pressure or high discharge temperature – or worst case that the compressor fails due to the break down of oil at too high operating temperatures.
Inspections and gas detectors
Why don't regulations on 'leak inspections' and refrigerant gas detectors solve the challenge? Scheduled leak detection has the obvious drawback of only taking place once or twice a year. On top of that, it is often very challenging or even impossible for the technician to ensure that there are no leaks – the refrigerant pipes
can be long and parts of it not easily accessible or not accessible at all, for example in heat exchangers, safety relief valves and generally in areas with forced air or wind. Many leaks will not be identified by an
inspection. Fluorescent dyes can increase detection as long as sites are rigorously cleaned after each leak – a site that looks like Piccadilly Circus at night when the fluorescent light is turned on will not make anybody happy. An oil change has to be extremely tidy if there is a fluorescent dye in the oil. I have seen sites where you can follow years of technicians walking around by the footprints on the floor and seen how dye smears have left glowing marks everywhere making any detection of fresh leaks impossible.
Gas detectors can reduce the requirements for leak detection inspections and are required for large refrigerant charges of HFCs but they are far from foolproof too. Refrigerants are heavy and there are requirements on machine room ventilation to avoid risks of accumulation of refrigerants that could be hazardous if allowed to build up. A gas detector must be located below the leak and before the gas is dispersed by the ventilation. In practice it can be unrealistic to install a sufficient number of sensors to catch all leaks.
Gas detectors are therefore often located to catch from critical leakage points such as relief valves, shaft and o-ring seals and flanges based on experience.
Indirect leak detection The idea of using 'indirect leak detection' is often neglected in spite of the fact that it is a reliable method which many systems can effectively. Indirect leak detection can monitor when just a small portion of refrigerant has escaped long before it would cause alarms or reduce capacity to cause complaints. If an indirect leak detection monitoring system that alerts a responsible person when there is a leak is implemented, the number of inspections can be reduced to half according to the F-gas regulations because all leaks will be detected when they occur – not when the next inspection is scheduled or when the system trips due to low charge.
A change of refrigerant charge will change operating parameters in a predictable way. 30 December 2021 •
www.acr-news.com
Monitoring refrigerant charge Indirect leak detection is based on using a system that continuously monitors the refrigerant charge in the system. As the refrigerant circuit is a closed loop with four main components (in a basic circuit) a given amount of refrigerant will always result in a certain operation at each operating condition. This means that any change of refrigerant charge will change how the system operates and can be detected through performance monitoring. If we look at the principles of a basic circuit we have two heat exchangers, one compressor and an expansion device in a circuit filled with a refrigerant that is liquid, vapour or two-phase. The change of state is used to absorb energy in
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