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8.3.1 HFC-134a and HFC blends R-407C, R-417A and R-410A HFC-134a, R-407C and R-410A are widely used in water and space heating heat pump systems and are well commercialised globally. R-417A is considered as a replacement for HCFC-22 in air conditioners, however, it is used in both existing heat pump applications and in new equipment. In the countries where HCFC-22 consumption reduction started in advance of Montreal Protocol requirements (i.e., mainly in Europe), these refrigerants are being used in water and space heating heat pumps with high to low sink temperatures. In Japan, R-410A is used; HFC-134a and R-410A are used in Canada and USA and to a lesser extent in Mexico and the Caribbean countries. R- 407C has been used to mainly replace HCFC-22 in existing product designs because of the minimal design changes that are required. However, the use of R-407C is declining in favour of the higher efficiency and lower system cost when applying R-410A (UNIDO, 2016). In order to adequately use R-410A, design changes are necessary to address its higher operating pressures and to optimise the system taking into account its properties, thereby achieving higher performance. Air-to-water split cascade systems are put on the market, using R-410A for low temperature circuits and HFC-134a for high temperature circuits. They both guarantee high seasonal COP in case of colder climates, even at high water sink temperatures approaching 80°C, while delivering the required heating capacity without any auxiliary electrical heaters. Both refrigerants are mostly used for combined space and hot water heating in order to replace existing boiler systems (Long et al., 2018; Dong et al., 2018). The energy efficiency of R-407C systems is typically lower than that of HCFC-22, although similar COPs can be achieved with a careful design of the system. In practice, R-407C shows a pronounced temperature glide during evaporation and condensation, which can lead to operational difficulties (Linton et al., 1996). R-417A has been used by some manufactures for heat pump water heaters. R-417A provides lower capacity than HCFC-22, however, has demonstrated effectiveness at higher temperatures. As the cost of the refrigerant itself is minor in comparison to the total system cost, small differences in the costs for the refrigerant therefore have minor effects. The cost of the components has a major impact. A more compact design generally results in lower costs. Compared to small systems, the design pressure has a larger impact on the cost for larger systems. For small and medium size systems, R-410A is the most cost-effective refrigerant, while HFC- 134a tends to be more cost effective for large systems. At the moment, there are no significant barriers to the use of these refrigerants, but their high GWP may put them under pressure, requiring a change towards lower GWP fluids. 8.3.2 HFC-32 The use of HFC-32 in water and space heating heat pumps is already commercialised on a larger scale. Moreover, applying HFC-32, similar units operate with a higher COP than with HCFC-22 or R-410A (Shigehara, 2001). HFC-32 has saturation pressures slightly higher than the one of R-410A, which is approximately 60% higher than the one of HCFC-22. System refrigerant charges can be up to 43% lower than for HCFC-22, while the energy efficiency is the same or higher (Yajima, 2000). HFC-32 has better thermodynamic properties and heat transfer performance than R-410A. Since HFC-32 has higher discharge temperatures than R-410A, a more accurate temperature control is necessary, particularly for high temperature water and space heating heat pumps and low temperature heat sources (Konghuayrob and Khositkullaporn, 2016). 2018 TOC Refrigeration, A/C and Heat Pumps Assessment Report 159PDF Image | Heat Pumps Technical Options
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