Chemical manufacturers have come up with a new refrigerant for vehicle ac systems but does this new family of gases have potential for stationary applications? Neil Everitt investigates.
THE changes imposed on the refrigeration industry over the last 20 years, particularly in respect of the refrigerants we use, is unprecedented.

Many readers will have lamented the demise of CFCs and are tackling the painful process of HCFC phase-out. Even current, industry-standard HFCs have come under environmental pressure for their global warming potential.

As a result, many companies have been investigating natural alternatives like CO2. But is there a fourth generation environmentally-friendly fluorocarbon refrigerant waiting in the wings?

Leading chemical manufacturers including DuPont, Honeywell, Arkema and Ineos Fluor have been investigating the potential for HFOs - hydrofluoro-olefins - for use in vehicle air conditioning systems.

Unlike their fluorocarbon predecessors, the new gases have a zero ozone depletion potential and meet EU regulatory requirements requiring gases with GWPs lower than 150.

The first such gas, HFO-1234yf, has been suggested as a possible replacement for R134a in vehicle air conditioning systems. Described as a 'near' drop-in and with a GWP of just 4, HFO-1234yf is seen by the fluorocarbon producers as the ideal alternative for the automotive industry which has also been considering the high pressure natural refrigerant CO2.

Honeywell is also offering a hydrofluoro-olefin as a new foam blowing agent for one-component foam and aerosol applications in Europe. Known as HFO-1234ze, it, too, replaces R-134a in one-component foam and aerosol applications.

R&d effort

A Honeywell spokesman has told ACR News that the company was looking at the use of HFOs in stationary applications: 'We are looking into that as well - we are developing our HFO platform to cover more and more applications.'

The latest issue of compressor manufacturer Bitzer's well-respected Refrigerant Report reveals some of the chemical characteristics of 1234yf.

According to the report, for the usual range of vehicle air conditioning operations, cooling capacity and COP are within 5% of R134a. Critical temperature, pressure level, vapour density and mass flow are also similar, whereas the discharge gas temperature is up to 10K lower.

On the minus side, the characteristics that give it its low GWP - its rapid decomposition in the atmosphere - may also work against it. Bitzer's Refrigerants Report questions the gas's long-term chemical stability in commercial ac and heat pump systems.

Flammability

Flammability may also be an issue. 1234yf is mildly flammable as measured by ASTM 681 and a probable ASHRAE rating of A2 (R134a is A1). Honeywell's studies have concluded that the flammability risk of 1234yf is significantly less than that of gasoline.

Indeed, the Society of Automotive Engineers (SAE), a body made up of major car manufacturers including Chrysler, Ford, General Motors, Fiat, Jaguar, Land Rover, Hyundai, PSA, Renault and Toyota, recently gave it a clean bill of health.

Flammability tests carried out by SAE at independent labs have not indicated flammability risks either in the passenger compartment or engine compartment.

In the event of a car fire, HFO1234yf --like other materials found in an automobile such as plastic parts --will burn and release hazardous materials. However, there have been no documented cases where combustion of automotive refrigerants has resulted in injury or death.
Flammability tests carried out by SAE at independent labs have not indicated flammability risks, either in the passenger compartment or engine compartment.

Toxic hydrogen fluoride (HF) can be formed when fluorine-containing refrigerants are exposed to an open flame but, again, this is seen as low risk. Tests carried out on behalf of SAE have confirmed the amount of HF formed in the event of a fire is extremely low and similar to R134a, for which there has been no reported incidents over the 16 years it has been used in vehicle air conditioning systems.

Despite, these seemingly 'green' characteristics, environmental groups are, inexplicably, still unwilling to accept this fluorocarbon alternative. Bodies like Greenpeace still back CO2 as the replacement for R134a in vehicle air conditioning systems.

This is despite lifecycle climate analysis tests by SAE which indicate that CO2-based solutions will produce 10-15% more total CO2 equivalent emissions than a HFO-1234yf solution.

However, the issue of flammability may not arise with the use of HFOs in stationary equipment as 1234yf is unlikely to be suitable.

However, according to a Honeywell spokesman, the previously mentioned foam blowing gas HFO-1234ze 'may have some applicability in certain stationary refrigerant applications with the added benefit of the product being classed as non-flammable.'

Meanwhile, the application of HFOs in stationary applications may still be some way off with the chemical manufacturers looking to test its effectiveness in vehicle air conditioning systems first. Certainly, the commercial compressors manufacturers have not yet had a chance to test the new gas.

A spokesman for Bitzer in Germany said that they were awaiting the arrival of a small test sample, but it would then be at least six months before they would have any useful data.

Copeland said that it would support HFO derivatives for stationary applications, once sufficient information and refrigerant samples become available from Honeywell/Dupont, but the spokesman added that this seems to be several years away.