Recent activity suggests that air conditioning may have a flammable future. Neil Everitt investigates
Remember those days when any new refrigerant was required to be non-toxic and non-flammable? In the current drive towards low GWP refrigerants that time may be an increasingly distant memory.

All the indications suggest that contractors will soon need to become fully acquainted with the different requirements of handling flammable and, most likely, 'mildly flammable' gases.

The HFO refrigerant 1234yf is now coming on-stream and its older sister gas 1234ze, originally seen mainly as a low-GWP insulation propellant, is increasingly finding its way into commercial products as a potential alternative to R134a, R404A and even hydrocarbons. HFO blends, their composition still a closely guarded secret, are also undergoing trials. What these blends have lost in flammability they've gained in GWP, but they are still way below the GWPs of current refrigerants.

The adoption of HFOs in stationary systems has been led by the UK. Klima-Therm's trials with 1234ze in chillers have been well documented.

While those 'in the know' seem somewhat reticent to confirm a flammable future, all the signs point in that direction. The F-gas review proposals document confirms a move towards low-GWP refrigerants and seeks to bring in compulsory training and certification to cover the so-called 'natural refrigerants'. The European contractors' body AREA has recently published guidelines for working with low GWP gases and the British Refrigeration Association followed this with its own guide to flammable refrigerants.

HFOs are, in reality, HFCs under a slightly different acronym. To the chemist, HFOs are unsaturated HFCs but, like HFCs, are composed of hydrogen, fluorine and carbon atoms. They are distinguished from HFCs by being derivatives of alkenes (olefins) rather than alkanes. This, on the face of it, minor difference makes HFOs very reactive, a characteristic which gives them a short atmospheric lifetime and, consequently, a low GWP.

Unfortunately, the pure physics of HFCs and HFOs means that low GWPs are achieved at the expense of flammability. They are, however, with their A2L rating, less flammable than hydrocarbons. Producers go further to argue that the HFOs, while 'mildly flammable' under distinct circumstances, have a much slower burning flame than other A2 gases.

Legitimately sneaking into the A2L classification is R32, an HFC refrigerant we may well be hearing a lot more of in the future as a single component gas for air conditioning applications.

R32 was one of the refrigerants evaluated by fluorocarbon refrigerant pioneer Thomas Midgeley in the 1930s but was largely ignored due to the development of other, seemingly more appropriate non-flammable gases. Interest in the refrigerant was renewed in the 1960s with the need for lower temperatures brought about by the growth of the frozen food industry but, again, its negative characteristics of flammability and higher operating pressures and discharge temperatures worked against it. However, it was considered and subsequently used in blends with other components.

In recent years, with the drive to lower GWP refrigerants, flammability is becoming less of an issue and R32 is very much back on the agenda either as a single component or in blends with HFOs. And R32 certainly has some positive attributes: a high refrigerating capacity, good heat transfer characteristics, admirable COPs and good thermal stability.

Positive test results

One of the biggest champions of R32 has been Daikin. At the end of September, and buoyed by positive test results, the Japanese manufacturer announced its adoption in all future residential air conditioners and into commercial units in the future.

A statement from Daikin's headquarters in Japan said it considers that HFC32 is suitable for split air conditioners and heat pumps.

The predominant Japanese manufacturers have tended to introduce any 'new technology' in its home country first before releasing it to the rest of the world. It was the case with VRF technology, both two-pipe and three-pipe, and to a large extent with the latest heat pump offerings.

Daikin Europe, with its headquarters and factory in Ostend, has achieved a degree of autonomy from its Japanese parent, but is unlikely to ignore what is happening in the Far East. Daikin Europe has admitted that R32 has potential for the European market, but warned that it had to ensure all aspects of the product life-cycle, for example training for installers and availability of R32 cylinders were in place before R32 could be launched in Europe.

R32 is currently twinned 50/50 with R125 to form R410A - the current industry standard refrigerant for air conditioning. By all accounts, it is an efficient refrigerant with a GWP of 650 - relatively low in the global warming league table.

However, back in the day when the flammability of R32 was considered unacceptable, R125, a high GWP refrigerant, was added to act as a suppressant.

Now presented with a clean sheet of paper, R32 is back on the agenda.

So what are the other major manufacturers up to? Mitsubishi Electric is involved in R&D of air conditioners that use R32, but intends to proceed by reflecting the guideline currently being considered by the Japanese refrigeration and air conditioning association JRAIA and the results of tests by the engineers society JSRAE.

Mitsubishi also has a patent on an air conditioning unit using R32, and using blends with 1234yf and with 1234ze.

There is considerable activity in the Far East, with all manner of flammable and mildly flammable refrigerants being investigated and in some countries - China, for instance - actually being adopted. These include propane, R32 and the little-known R161. With many systems running on R22, many developing countries are looking to bypass R410A altogether and go straight to a fourth generation gas.

Last year, Indonesia announced that it had chosen R32 as its replacement for R22). The Indonesian government plans to promote the use of R32 with the support of the United Nations Development Programme for refrigerant conversion and is also making use of the expertise of the aforementioned Japanese association JRAIA (Japan Refrigeration and Air Conditioning Industry Association).
According to their plan, Indonesia will complete the conversion to R32 by 2015. With help from the Japanese Ministry of Economy, Trade and Industry, a conversion project was established. Significantly, Daikin, Panasonic, Fujitsu General, Toshiba and Hitachi were all named as companies contributing to the effort.

The major compressor manufacturers have also been carrying out tests. Research presented at the Purdue University compressor conference by Hung Pham and Rajan Rajendran of Emerson Climate Technologies concluded that, even in a drop-in evaluation, R32, in terms of efficiency and cost, was an attractive solution for mainstream air conditioning and heat pump applications with performance comparable to R410A.

Emerson also provided comparisons with a number of HFO blends which were found to be comparable to R32 but were hampered by their much higher cost.
R32 also performed better than the 'natural' refrigerants CO2 and propane due to their low efficiency and/or flammability. Propane they saw as being limited to much smaller units.

Tests by Danfoss found a better system efficiency compared to R410A and the benefit of a smaller refrigerant charge. The significant downside to this gas is its high discharge temperature. Danfoss observed the resulting oil degradation which could result in various compressor failures like bearing seizure and low system and compressor efficiency. It sees liquid injection as a possible solution.

The Danish manufacturer exhibited a new range of R32 Scroll compressors at Chillventa in October. Other compressor manufacturers are also known to have investigated the potential for R32 in a number of different heat pump and air conditioning situations.

The air conditioning industry has had little, if any, previous experience of flammable refrigerants. However, with the drive towards lower GWPs and new European standards which will allow larger flammable refrigerant charges, it seems likely that flammables will become commonplace in the future.

// The author is editor of ACR News //