Refrigeration refresher

Refrigeration and air conditioning systems are rarely adequately maintained, with the result that many systems are storing up potentially catastrophic problems. Colin McNicholl explains how regular refrigerant analysis can ward off the dangers.

Refrigerant analysis is recommended as a routine step for all operators of critical plant, but it is rarely carried out. Many users are familiar with the concept of oil testing and vibration monitoring as part of routine maintenance programmes, but testing of the refrigerant circuit is almost totally ignored to the peril of thousands of systems around the country. Regular testing and remedial works would dramatically lengthen the lifetime and reduce the running costs of literally thousands of highly expensive systems.

At BOC's laboratory in Immingham near Grimsby we receive samples directly from end users either if a problem has been detected with the running of their plant or as part of a planned maintenance programme. Depending on the substance under test, chemical or instrument-based analysis is carried out.

The science is far from 'rocket' and can be carried out extremely quickly. Overnight couriers bring samples to the lab and results are returned within three days. This should be regarded as a routine first step for all plant operators, especially today when users can ill afford unscheduled system shutdowns.

However, the sampling service is used on only a fraction of the systems that could benefit from it. The big problem is that contamination of the refrigerant or water ingress can build up undetected until you have a serious problem such as a compressor burnout. Problems can be brewing away unless the system is sampled and tested every six months or so.

A standard oil test will show if an oil change is due. BOC's oil testing includes ferrography technology, which is an accurate and reliable process to predict wear conditions and the failure potential of lubricated components. This test is performed to determine severity, origin and development mechanism of wear particles. Testing of the refrigerant is equally important.

Acidity and moisture tests are very important. BOC has uncovered problems with high levels of moisture in the refrigerant, often caused by allowing air into the system during maintenance or through leaks. Dryers can ensure the gas goes in dry at the start, but they can't guarantee it will stay that way. Dryers can also cope with low levels of moisture within a system, but if there are very high levels of moisture the dryer core material can become waterlogged and break down. At this point you not only have a problem with moisture, but also have dryer core 'sludge' circulating around the system. Many of the systems work below atmospheric pressure so will draw in air if they are opened up for maintenance and the hygroscopic oils used will attract and retain water droplets from the air.

Moisture inside high temperature equipment will lead to acidic breakdown of the insulation on the motor windings. This has become more of an issue with the phase-out of chlorinated refrigerants. HFCs have a greater affinity for water whereas the now discredited CFCs and HCFCs had much lower saturation points. At the moment, the majority of tests are for R22, but we are now seeing a lot more R407C and R134a coming through where the issue of moisture is prevalent.

In the industry, oil testing is an established principle, but testing refrigerant gas is not. We have to change this mindset. The BOC lab receives three times as many samples for oil testing as for refrigerant — and really it should be about an equal proportion with far higher numbers overall.

Moisture and oil ingress along with loss of refrigerant charge is constantly eroding the performance of chiller and process plant. According to ETSU’s Good Practice Guide 178, a 15% leak can halve the system capacity, which doubles the running cost. Reduced capacity will also struggle to cope with peaks in demand.

BOC has carried out a number of full inventories on large systems, where the entire refrigerant charge has been removed, tested and weighed. In every case, the system was considerably undercharged and, therefore, not performing as designed.

A system designed to operate with a charge of 5.7 tonnes will still work even with two tonnes of charge missing, but it will have to run for more than double the design hours to meet the cooling load. That drives up energy costs and degrades the equipment.

On every occasion where we have removed all the product from a chiller and weighed it, or made a judgement based on the level indication on the receiver vessel, the actual charge has been considerably less than it should have been — and the client/chiller operator was totally unaware of this. The negative impact on plant efficiency is significant.

Testing kits are available through branches of BOC’s distributor HRP so engineers can take their own samples and send them away to Immingham for analysis. After testing, the user will receive a detailed report on their particular problem. Having read this, they may decide that they need more specialist support as a result of the test.

In that case, it is possible to put the ailing system on the refrigeration equivalent of ‘dialysis' using a unit called the Zugibeast. This is a new piece of equipment for the UK, which is able to separate contaminants from refrigerant in a working system on site, clean and return it without having to shut down the plant.

Enter the Beast

Last year BOC signed a technology alliance with Hudson Technologies, whose chief executive Kevin Zugibe invented the 'Zugibeast'.

It is something of a misnomer as the piece of kit is not much larger than a domestic washing machine, is easily transported to site in a transit van and will fit through a standard-sized door. This gives it the huge advantage of being deployed on the end user's premises right next to the chiller or refrigeration machine requiring attention — but it is still capable of processing 2 tonnes/h of refrigerant.

It will decontaminate and replace the refrigerant around ten times faster than anything seen before in the UK and the plant can remain in operation the whole time. The Beast uses the plant's own refrigerant charge to carry out a deep clean. The refrigerant is boiled and then flushed through the system to take out any deposits and sludge that reduce heat transfer efficiency.

Using its own refrigerant as a cleaning agent ensures this is a non-aggressive approach for the equipment, as it does not subject the mechanical plant to anything ‘alien’ and likely to be non-compatible.

The Beast separates the deposits and water from the clean refrigerant through a filter and a second ‘dry' filter takes out any remaining moisture at the end of the cycle. Large amounts of oil and debris are invariably extracted from the refrigerant side by the process. Oil should make up around 3% of the total volume of the liquids within a refrigeration system, but we regularly encounter examples where it is more than 20%. The Beast can separate and drain off the full charge and restore the right balance.

Being able to put the system back in order without taking it off-line is a big bonus for users such as large chemical, petrochemical and food plants that use refrigeration for process cooling or heat extraction. They also end up with a more efficient refrigeration unit leading to fuel bill savings and increased output. Maintaining refrigerant systems at optimum performance is also an important way of reducing the energy waste in a working plant.

Colin McNicholl is Refrigerant Services Manager at BOC.