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7.3.8 HC-1270 HC-1270 has favourable characteristics from the point of view of both thermodynamic and transport properties. It is a class 3 flammable refrigerant. Its performance has been evaluated, where the cooling capacity is up to 10% higher than HCFC-22 and COP up to 4% higher. Further discussion on HC-1270 is in (UNEP, 2015). 7.3.9 R-744 R-744 has a low critical temperature, which results in significant efficiency losses when it is applied at the typical indoor and outdoor air temperatures of air-to-air air conditioning applications without adjusting the refrigeration system and adopting certain technologies accordingly. Air-cooled R-744 air conditioning systems are available in capacities from about 3 to 300 kW. Experimental results show that R-744 systems may compete in energy efficiency with high efficiency R-410A systems for moderate climates in both cooling and heating mode; however, improvements are needed to significantly increase the capacity, efficiency and reduce the peak electrical power requirements during the cooling mode in high ambient conditions (Jakobsen et al., 2007; Okamoto, et al., 2016). Work is still on going to try to improve performance of R744 systems for AC and HP systems. For example, Lee et al (2014) demonstrated that improvement approaching 10% can be achieved with optimised ejectors. One study (Calabrese et al., 2015) investigated the feasibility of R744 in “rooftop” ducted systems. Whilst not comparing experimental results directly against those for conventional systems, the authors determined that the COP is likely to be lower than for conventional HFC systems when the ambient is above 16°C, but could offer substantially better performance when temperatures are below 10°C. Further to the previous 2014 RTOC Assessment Report, there have not been major developments reported. Further discussion on R-744 is in (UNEP, 2015). 7.3.10 New mixtures for air conditioners There are a number of new mixtures emerging for potential use in air conditioning, which include: R-444B, R-446A, R-447A, R-447B, R-452B, R-454A, R-454B, R-455A, R-459A and R- 511A. All have saturated vapour pressure and volumetric refrigerating capacity characteristics that approximately span the range between those of HCFC-22 to R-410A and are potentially feasible for use in many types of air conditioning systems. All except R-511A have class 2L flammability (except R-511A, which is an A3 flammable refrigerant) and thus have maximum charge sizes constrained according to the limits detailed in the Annex to Chapter 2. As with all flammable refrigerants, systems should be designed, constructed and installed with due consideration of their flammability, as well as due consideration to reclaim and recovery requirements during servicing and at end of life. For all these mixtures, cost implications should be comparable to those of HCFC-22 and R-410A, although likely slightly greater due to the present higher refrigerant prices. Currently manufacturers and institutes across several countries are testing and trialling these various mixtures. R-444B R-444B has efficiency comparable to that of HCFC-22 and the liquid density indicates that the charge should be about 10-15% lower than HCFC-22. Preliminary test results indicate that R- 444B shows similar capacity and efficiency to HCFC-22 (Sethi et al, 2014) and is expected to perform similar to HCFC-22 systems at high ambient temperatures; theoretical cycle performance 2018 TOC Refrigeration, A/C and Heat Pumps Assessment Report 143PDF Image | Heat Pumps Technical Options
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