Low GWP refrigerants
Legislation driving innovation
The European Parliament has adopted a compromise agreement, made in December 2013, to phase down the use of hydrofluorocarbons (HFCs).
The fluorinated gas (F-gas) is just one that makes up an estimated 2% of European emissions for greenhouse gases. This makes it a major contributor to global warming.
The new agreement is expected to lead to caps on the volume of HFCs that can be sold within the European market in terms of equivalent Carbon dioxide (CO2), gradually reducing the amount to 21% by 2030. The EU has further agreed a ban on the use of HFCs in new equipment in a number of sectors, most notably commercial refrigeration by 2022.
As a consequence, higher global warming potential (GWP) refrigerants such as R410A and R134a, which have GWPs of 2088 and 1430 respectively, may see some volume reductions in the market from as early as 2017.
To meet forthcoming changes in regulations, hydrofluoroolefins, also known as unsaturated hydrocarbons, are considered to be the most viable platforms, with R1234ze ('ze') and R1234yf ('yf') singled out as the two main isomers considered to have real applications in the cooling industry.
Low GWP alternatives
As one of the first UK manufacturers to launch a production range of BSI-approved free cooling chillers incorporating 'ze' and with the likelihood of market restrictions looming fast on the horizon, we are moving to extend our choice of low GWP alternatives available to customers across our range of cooling products, including TurboChill™ chillers in DX, free cooling and a new water cooled variant. Indeed, our first production R1234ze chiller is currently cooling John Lewis’s new store in York.
GWP is a measure of a greenhouse gas when it is released into the atmosphere and benchmarked against CO2 which has a GWP equal to one.
So-called ‘natural’ or ‘stable’ gases such as carbon dioxide, methane and butane, do not break down in the atmosphere and are non-flammable. They are, however, generally less suited to large volume air conditioning and IT cooling applications.
In contrast, the more volatile nature of the latest ‘fourth generation’ refrigerants, which include 'ze' and 'yf', means they break down more readily in the atmosphere than their counterparts.
By way of comparison, 'ze' can take just 16.4 days to break down, compared with 14 years for R134a.
Compared with 'ze', 'yf' has a shorter reactive life time of just 10.5 days.
'yf' is, however, more complicated to manufacture and therefore represents a less cost-effective solution for large-scale production and use in high-capacity equipment such as chillers.
Originally considered to have 100-year GWPs of six and four respectively, recent studies by the Intergovernmental Panel for Climate Change have indicated that 'ze' and 'yf' have GWPs lower than 1, which is better than the GWP of CO2. In contrast, R134a has been rated at 1430.
In the case of the chemical formula CF3CH=CHF (tetrafluoropropene), 'ze's double carbon bond means it is more reactive and it is this bond that enables this gas to become benign in terms of GWP.
Classed as ‘unstable’ in the atmosphere, the reactive nature of its molecular structure increases its propensity to break down in the atmosphere. As a result, 'ze' has a much lower impact on global warming than other gases that remain stable in the atmosphere for hundreds of years.
No-one could have missed the debate over the flammability of 'yf', which has seen a protracted dispute in the German automotive industry over the mobile air conditioning directive to phase out and replace R134a.
The European Commission’s top scientific and technical body, the Joint Research Centre, has concluded that 'yf' is safe for use in automobiles and that there is no sufficiently supportive evidence of serious risk.
Whereas 'yf' and 'ze' are categorized in the same safety class and fluid group (A2L and 1 respectively) by a draft version of EN378, 'ze' is generally deemed to be non-flammable for transport and storage because it is not combustible below 30°C, outperforming its ‘yf’ counterpart.
Even at temperatures higher than 30°C, 'ze’s flammability characteristics are exceedingly low.
To burn, 'ze' needs the combination of a powerful ignition source, more than 5,000 times higher than gases such as methane, propane, acetylene and R152a while having a concentration between its lower flammability limit and upper flammability limit – flame limits that fall within a smaller envelope than those for 'yf'.
When higher ignition levels within its relevant flammability limits are reached, 'ze' takes more energy to ignite than 'yf' and burns at a lower velocity. Furthermore, if the ignition source is removed, the flame is immediately extinguished.
Performance of next generation refrigerants
Despite cooling capacities that are about 25% lower than those achieved with R134a, R1234ze requires lower mean power inputs of 26%, which results in a better coefficient of performance (COP) ratio of about 3%.
Best practice in system design to maximize air flow and heat exchange, including integrating subcoolers and economizers with intelligent controls logic, will ensure that the highest energy efficiency ratios and cooling power per footprint are achieved.
A further benefit associated with 'ze' is that Building Research Establishment Environmental Assessment Methodology (BREEAM) points will be easier to obtain in new installations.
Airedale’s TurboChill Free Cooling chiller with R1234ze, for example, automatically receives two BREEAM points for its low global warming potential characteristics.
In contrast, R134a TurboChill TCC and TurboChill Free Cooling TCF variants receive one point for their Direct Effect Life Cycle CO2 equivalent emissions of =1000 kgCO2e/kW cooling capacity and a further point for leak detection and automatic shut down and pump down of refrigerant.
'ze' is certainly a good drop-in replacement for R134a. Available at a lower cost per kg than 'yf' for a similar COP. 'ze' has also been proven to be less flammable than 'yf' and has more flexibility from an ATEX [explosive atmosphere] perspective.
We continue to work closely with the major compressor manufacturers who have now adopted 'ze' for future development, to offer the new refrigerant across all viable Airedale products including chillers, condensing units and rack-based systems.
Given its low GWP characteristics, there will be no restriction in the mid to long-term on the usage of 'ze'.