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Why HFO refrigerants are the future for chillers

Based on the evidence he has seen to date, Ken Strong believes that HFOs will become the new mainstream refrigerants of choice for chillers in the next few years
For the past decade or so, HFC refrigerants have provided a safe and efficient option for use in chillers for air conditioning and process cooling. However, there is now a serious question mark over the future of HFCs due to their high Global Warming Potential.

The latest EU measures, published towards the end of last year, propose strict new controls on the use of high global warming refrigerants. If implemented as envisaged, this could seriously impact the ability of our industry to use some HFC options in the future. The situation is likely to come to a head in three to four years as the HFC phase-down begins to bite.

Informed end users are already getting nervous of investing further in HFC technology due to the clear direction of policy and the possibility of a future ban on the use of high global warming HFCs.

For those with memories long enough to recall the CFC crisis of the Eighties, there is an unmistakable sense of deja vu about the present situation. Then, CFCs were consigned to the waste bin due to their impact on the ozone layer, to be replaced by much less harmful HCFCs, such as R22.

End users invested heavily in HCFC-based plant and equipment as the new 'safe' option. However, it was not long before HCFCs themselves were in the dock and also being phased out, as a result of their albeit reduced impact on the environment, with consequences for the life-span of equipment bought in good faith.

The solution to the HCFC problem was of course HFCs, which have zero ozone depletion potential. As a result, refrigerants such as R134a, R410A and R407C became the mainstream gases of choice for the air conditioning industry.

The problem with HFCs, as some pointed out at the time, is that while they do not harm the ozone layer their high global warming potential is a serious Achilles heel. That point of weakness is now threatening their continued use as the mainstream refrigerants of choice of use in chillers and air conditioning.

HFO refrigerants are the next generation of fluids waiting in the wings. Unlike their predecessors, they have very low global warming potentials - just 6 for HFO1234ze compared with 1300 for HFC134a. Another HFO fluid, R1234yf, has an even lower GWP of 4. This is currently going through the safety testing and approvals process.

Recent changes to the BREEAM criteria mean that HFO1234ze now attracts environmental sustainability points under the programme, as well as HFO1234yf, as it now qualifies as a very low GWP refrigerant.

How aware are industry and end users of the issue and the benefits of using HFOs? Over the past year, we have seen increased interest in HFOs, driven by concern over future supplies of HFCs. John Lewis Partnership has been notably active with its suppliers on trialling HFO-based cooling at stores.

Are there any viable alternatives to HFOs that could be harnessed for use in chillers?

Carbon dioxide has been used in some supermarket refrigeration equipment. However, the high operating pressures with CO2 are a concern, as it requires heavy duty plant and specialised manpower to install, commission and service it. There have been safety issues reported which have made some end users nervous of adopting CO2 systems.

Hydrocarbons as refrigerants offer the possibility of good efficiencies. However, the problem of flammability remains a significant concern. There are also strict limits on the size of charge that can be used per refrigeration circuit; therefore single unit capacities are generally limited to 250kW, which in chiller terms is obviously a major constraint.

Health and safety issues
Ammonia is a highly efficient refrigerant, but obviously comes with a whole host of health and safety issues relating to its use, particularly near public places. Equipment has to be carefully designed and manufactured, and it requires specially trained engineers. Capital costs are also high due to the nature of the equipment and mandatory safety measures required.

Against this background, HFOs would appear to offer the best combination of efficiency, ease of use, safety and cost. On the environmental front, HFO1234ze has a negligible GWP and, technically, is an excellent substitute for the widely used R134a refrigerant.

One of the major obstacles to wider adoption of HFO-based systems has been the high cost of the refrigerants which, until recently, were only available in limited 'test' quantities. Today, however, the refrigerants are now in full scale commercial production and the price has fallen much more in line with that for HFCs.

While HFOs cannot quite be used as a straight drop-in replacement for HFCs, relatively few design changes are required to make equipment and components compatible. It is considered safe and non-toxic and can be handled by engineers without the need for specialist training.

In terms of performance, chiller tests with HFOs at standard operating conditions have shown that, compared with R134a, a higher volume of HFO (around 23 per cent more) has to be circulated to obtain the same cooling capacity. This means a slightly larger compressor must be used. However, taking this into account, the overall efficiency of an HFO system is improved by about 5per cent.

After detailed testing and evaluation by the manufacturer, an HFO version of the high efficiency Turbomiser chiller is now available, running on HFO1234ze. The only changes to the design required were new seals, due to a materials compatibility issue, and an update to control software.

Four Geoclima chillers operating on HFO1234ze are currently installed in the UK and reported to be working well. Two are based on Turbomiser oil-less magnetic levitation system.

// The author is managing director of Cool-Therm //
24 June 2013

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