The national sales manager at Johnson Controls, Barry Abboud, and the company's market analyst for chiller solutions, Jill Woltkamp, share insights on how to make a safe transition to next generation refrigerants.
Prior to the 1930’s, inventors used a variety of available chemicals to develop their ice machines and refrigerators. Some of these refrigerants found in nature, were readily available, and are still used in the refrigeration industry today. Several, however, were highly volatile and were discontinued when synthetic chlorofluorocarbons (CFCs) were invented—R11 being one of the earliest and most successful.
With CFCs, refrigerant was considerably safer and was more efficient than most refrigerants that had been used to that time. Growth in the use of CFCs in both the air conditioning and refrigeration industry continued until the 1970’s when scientists connected the deterioration of the ozone layer above the Antarctic with their use.
By 1988, the Vienna Convention was entered into force, and the Montreal Protocol followed one year later defining the actions to be taken by both developed and developing nations to address ozone depletion. After the Montreal Protocol began the phase-out of CFCs, the HVAC industry has accelerated refrigerant development and testing in the search for more environmentally benign compounds, and, since the chemistry developments of the 1930s, the HVAC industry's primary concern has always been that of life safety.
Refrigerants are combinations of a limited number of elements with varying characteristics. Use of chlorine or bromine increase ozone depletion potential, while adding fluorine increases global warming potential. Adding hydrogen increases flammability but lowers atmospheric lifetime. The challenge to chemists is to create a workable balance between a multitude of considerations, including environmental impact and efficiency, while not compromising on safety.
Currently, the global HVACR industry is tackling the third paradigm shift in synthetic refrigerant chemistry – the first went from CFCs to HCFCs, the second, from HCFCs to HFCs, and now the third, from HFCs to HFOs, HFO blends, and other low-GWP options, such as natural refrigerants.
Each transition has reduced the atmospheric lifetime of the refrigerant molecule in question by an order of magnitude. For example, the atmospheric lifetime for CFC-12 is 100 years, HFC-134a is just over 10 years, while HFO-1234yf is only 10 days.
Refrigerant molecules that rapidly degrade can have less impact on the environment. But rapid decomposition in the atmosphere is another way of saying that these refrigerant molecules are less stable, and potentially can be flammable under certain conditions. More reactive chemicals can also be more toxic. As a result, the industry is committed to thoroughly investigating the safety of today's fourth-generation refrigerants, and making this transition is not without challenges.
ISO Standard 817 and ASHRAE Standard 34 classify both refrigerant flammability and toxicity. Letters A and B designate lower and higher toxicity. A number system denotes the level of flammability, with A1 for non-flammable, A2 for flammable, and A3 for higher flammability. In practice, the flammability and toxicity classifications are combined to indicate the general safety of the refrigerant. For example, HFC-134a is classified A1.
Recently, the new classification of 2L was created to indicate Mildly Flammable, which is defined as having a burning velocity (BV) of less than 10 cm/s. Compared to Class 2, Class 2L substances do not propagate readily a horizontal flame, only an upwards flame. Thus, a Class 2L refrigerant is effectively non-explosive if ignited, as the flame predominantly propagates in an upward direction and not rapidly outwards in many directions.
The current body of research has been largely influenced by refrigerant and some equipment manufacturers with a stake in greater adoption of these fluids. It is important that the continued work of third party independent research organisations validate this information and work across geographic borders to leverage the work done in different regions of the world.
Safety
Research, certifications, regulation and implementation take time. It is important to be thorough, not expedient, to ensure that this transition to lower GWP refrigerants is made without compromise. While some sectors of the refrigeration industry have utilised flammable refrigerants for some time, HVAC systems used for human comfort applications since the 1930's have traditionally used the safest Class A1 refrigerants, with the exception of HCFC-123, designated Class B1, under ASHRAE 34. Flammable refrigerants are uncommon in the HVAC industry.
The potential use of mildly flammable A2L refrigerant in HVAC applications affects equipment designs and standards, building and fire codes, construction practices, manufacturing processes, material handling and life safety procedures. All of which must be updated to ensure refrigerants can be utilised safely.
Manufacturers, aware of this transition process, are evaluating new refrigerants and other technologies to advance performance, cost and safety of their products. Most manufacturers have been monitoring, testing and prototyping many of these refrigerant alternatives for many years.
For today’s R-134a based centrifugal and screw chiller platforms for example, medium pressure HFO-513A refrigerant blend, serves as a good option in terms of safety, capacity and efficiency for future applications, as it is also Class A1 refrigerant, with similar thermodynamic properties and with 56 per cent lower GWP. For scroll chiller platforms, several potential alternatives have been identified that look attractive due to their performance.
For outdoor chillers, A2L flammability risks can be more readily addressed. However, flammability presents a greater challenge for indoor equipment and for direct systems like rooftops, split systems, VRF and unitary equipment.
These new HFO refrigerants, currently limited in their availability, generally come with price premiums when compared to today’s HFCs. However, this will change over time.
As the newer generation HFO refrigerants are introduced to the market, their adoption rate will be a function of available equipment, distribution, local inventory, local pricing, service infrastructure, industry training and building code revisions commensurate with the new, updated AS/NZ Standards 817 and 5149.
A HFC phase-down was agreed under the Montreal Protocol in Kigali, Rwanda, in October 2016. Developed countries, such as Australia, will phase‐down their production and imports of HFCs by 85 per cent between 2019 and 2036. Developing countries will also phase-down HFCs over a more extended time schedule.
The HFC phase-down is importantly and deliberately not a phase out. HFCs will incur a gradual reduction in the maximum amount permitted to be imported into Australia, beginning from January 1, 2018. The end point is an 85 per cent reduction by December 31, 2035, which equates to 1.607 Mt CO2‐e annually from 2036 onwards.
Efficiency
When we talk about the total environmental warming impact from an electric chiller (TEWI), we have to consider the sum of both the direct and indirect effects. The indirect effect is influenced significantly by the energy source mix of power generation and equipment efficiency.
To specifically calculate the indirect impact, energy consumption per year is multiplied by the indirect emission factor which is multiplied by the system operating life. The direct impact is calculated by multiplying the refrigerant GWP times the refrigerant charge (amount of refrigerant in the unit) times the leakage rate times the system operating life.
Manufacturers have made significant progress in recent years addressing the direct effect by reducing unit charge volumes through new heat exchanger technologies. Leakage rates have also been significantly reduced through improved equipment designs.
Hypothetically, if we could completely eliminate the refrigerant charge impact of a chiller, so we remove the direct effect component of the global warming potential entirely, we are only left with the indirect effect to consider. In this case, how much of the carbon footprint remains?
Surprisingly around 95 per cent of the total global warming impact remains due to indirect emissions from predominantly fossil fuel generated electric power. The important message here is that as we embrace a low GWP refrigerant future, we must not compromise and must continue to strive for higher levels of equipment efficiency.
HFCs are a type of synthetic greenhouse gases (SGGs) that contribute to climate change. As of 2013, synthetic greenhouse gases represented 1.8 per cent of Australia’s carbon dioxide equivalent (CO2‐e) emissions. The sequential reduction in import of HFC refrigerants permitted by the Australian Government under the Kigali phase-down agreement, is to ensure that this percentage does not continue to grow.
As the industry embraces the responsible transition to lower GWP natural and next-generation synthetic refrigerants, safety will always remain the primary consideration. Adoption of lower carbon intensity power will make a major contribution to reducing the significant indirect global warming effect of large electric HVAC chillers.
Notwithstanding, both today and in the future, it is paramount to ensure high levels of product, system and building efficiency, which provide the greatest potential to reduce our overall carbon footprint.