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Considering the various R-410A alternatives with medium and lower GWP, the majority of these are flammable to some extent. Alternatives with capacity and pressure comparable to HCFC-22, those with a GWP lower than about 600 tend to be flammable whereas those with higher GWP tend not to be (see Chapter 2 for more details). Appropriate measures have to be applied in order to mitigate the risk, for example, minimising the amount of refrigerant that can leak into occupied spaces or removing the refrigerant from the occupied space, ensure that probability of ignition is greatly reduced through risk assessment and at a minimum, meet the requirements of national regulations and/or appropriate safety standards (where they exist); such rules are continuously under development and refinement. A more comprehensive overview of applicable safety standards and recent developments in the field of safety of flammable refrigerants is detailed in the recent Task Force (TF) report under Decision XXVIII/4 “Safety Standards for Flammable Low global warming potential (GWP) Refrigerants”. Within the discussion of the various refrigerant options, numerous studies on performance are reported on. There are a wide variety of relative results amongst different units and conditions inferring that the influence of specific system design has a more pivotal influence on performance than any one refrigerant. Broadly for results that are within ±5% of the baseline, performance can be considered to be comparable. Measurements considering high ambient conditions are also reported upon, where available. 7.3.1 HFC-134a Whilst HFC-134a is a potential HCFC-22 replacement in air-cooled systems in limited product categories, it has not seen broad use because manufacturers have been able to develop substantially lower cost air-cooled air conditioning systems with other alternatives. Although it is seldom a cost-effective alternative, it has been used widely in regions that experience high ambient temperatures for a variety of different types of air-to-air systems. Further discussion on HFC-134a is in (UNEP, 2015). 7.3.2 R-407C Since R-407C requires only modest modifications to existing HCFC-22 systems, it has been used as a transitional refrigerant in equipment originally designed for HCFC-22. However, since around 2004 many of the R-407C systems have been redesigned for R-410A to achieve size and cost reductions. An exception is when the target market’s standard conditions are high ambient temperatures, such as above 40-55°C. Further discussion on R-407C is in (UNEP, 2015). 7.3.3 R-410A R-410A can be an alternative to replace HCFC-22 only for new equipment production, since the operating pressures are around 50-60% higher than HCFC-22. Due to its thermophysical properties, the design of R-410A units can be more compact than the HCFC-22 units they replace. R-410A air conditioners are currently commercially available globally. A significant portion of air conditioners uses R-410A. System designers have addressed the higher operating pressures of R-410A through design changes such as thicker walls in compressor shells, pressure vessels (accumulators, receivers, filter driers etc.). In addition, the considerations for lubricant requirements are as described for R-407C; POE or PVE have to be used. As concerns over GWP have increased, R-410A is becoming seen as a less viable alternative for HCFC-22 in the longer term, although it currently remains the first choice for new air conditioning equipment. In some product groups there is now a transition away from R-410A. Another concern is its low critical temperature that can result in degradation of performance at high condensing temperatures. Whilst R-410A systems have been demonstrated to operate at 2018 TOC Refrigeration, A/C and Heat Pumps Assessment Report 139PDF Image | Heat Pumps Technical Options
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