Open-access content Monday 15th October 2012
With the phase-out of HCFC refrigerants, there is much debate as to which refrigerant is best placed to replace the ones in use today, explains Graham Wright.
15 October 2012
The use of HFC refrigerants in air conditioning systems is a hugely complex issue.
There is much debate on which gas will be most widely adopted as the next-generation refrigerant for air conditioning, heat pump and chiller systems, in the hope of maximising energy efficiencies and mitigating future global warming impact.
The likely candidates are R32, Propane (R290), CO2 (R744), and HFO blends, each with its own advantages and disadvantages.
It is vital to assess the use of refrigerants based on five factors:
- Ozone depletion potential
- Global warming potential
- Natural resource efficiency
Ozone depletion potential must be zero.
This is a given (due to the global Montreal Protocol agreements and EU Ozone-depleting regulations) and requires no further justification. But Global Warming Potential (GWP) is slightly more complicated. GWP must be considered from an entire Life Cycle Climate Performance (LCCP) perspective.
This means that the total energy used over the life of one air conditioning or heat pump unit is converted to its global warming equivalent (indirect emissions), then the global warming equivalent of the direct refrigerant emissions is added to this. This method gives a much more accurate evaluation of the true global warming impact of a unit throughout its life-cycle.
Looking only to the GWP value is, therefore, not the correct way to assess refrigerant options, as a unit with a 'medium' GWP may have a lower total impact than a unit using a 'low' GWP refrigerant.
As it is predicted that 75 per cent of future HFC emissions will originate from developing countries, it is important to find solutions that are affordable on a global scale. It is also vital to be efficient with natural resources and the environmental and economic parameter to "do more with fewer materials" should be adhered to.
As such, refrigerant options must be assessed on their potential for reuse. For example, a single component refrigerant such as R32 has an advantage. This same rule applies to the assessment of raw materials used to manufacture equipment. So, even when low-efficiency refrigerant options could be improved by using more refrigerant in larger systems, this would be detrimental to the total eco-design balance.
It goes without saying that safety is paramount.
The ASHRAE 34-2010, ISO 817, EN378 standards on the designation and safety classification of refrigerants indicate that R32 can be applied safely in a wide range of applications. However, the thinking on safety varies considerably. Dismissing something as 'dangerous', without a more accurate risk analysis and serious consideration of the other issues, can and will limit the potential of air conditioning to become a genuinely sustainable industry.
Many factors affect safety, including product type, volume of refrigerant charge, room size, and capacity of switch type in the room; ignition does not usually occur from the type of electrical capacity used in domestic switches.
It is also important to understand the scale of the risk. With R32, for example, even when performing soldering work, a flame will blow out naturally and not continue to burn because the flow of leaking refrigerant is faster than the speed that transmits combustion.
Tests carried out by Daikin Industries Limited and Suwa Tokyo University of Science (Experimental safety evaluation on flammability of R32 refrigerant, Yajima R et al, ICR 2011), show that even if combustion of R32 occurs, it is not explosive and the possibility of fire spreading is extremely low.
The efficiency question
While each of these points is important, it is also crucial that they are not focused on exclusively, without giving due weight to the issue of energy efficiency. Without the highest-possible levels of energy efficiency, future systems will require more power from natural resources and will emit more carbon than is necessary - a detrimental step in meeting the UK's tough carbon reduction targets.
The definition of energy efficiency needs to include, not just the seasonal efficiency averaged over the cooling or heating season, but also the efficiency in peak load conditions (on very hot or very cold days).
The first of these is important to reach the energy efficiency goals set by various EU directives (Ecodesign, Energy Efficiency Directive, EPBD, Renewable Energy Source Directive) whereas the peak-load efficiency is important to avoid the requirement for extra power plants.
Deciding upon a new refrigerant will be difficult and debate is likely to continue. The need to take up this challenge stems from the refrigerant industry's responsibility to protect the global environment and a drive for sustainable growth of the air-conditioning and heat pump market.
- HCFC refrigerants for air-conditioning, heat pump and chiller systems are likely to be phased out
- The next generation refrigerants will probably be R32, propane (R290), CO2 (R744), and HFO blends
- The aim is to maximise energy efficiency and mitigate future global warming impact
- Refrigerant choice should be assessed on ozone depletion potential, global warming potential, natural resource efficiency, affordability and safety over the lifetime of the products using it
- Energy efficiency is crucial to protect natural resources and minimise carbon emissions.