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alternative blends like R-450A and R-513A are also being evaluated. These and other similar lower GWP HFC/HFO blends are important not just for new systems, but also as replacements for existing systems that use R-404A and HFC-134a, as HFC phase-down regulations get implemented. HC-290 and HC-1270 Refrigerant changes have begun since the early 2000 in Europe, and especially in Germany, where propylene (HC-1270) has been introduced in supermarkets, using a secondary loop. HC- 290 is now the preferred option. For all HCs, the machinery room is located outside of the store. The number of these HC-systems is limited; however, charge reduction strategies can help in increasing the number of systems with such refrigerants. R-717 Due to its toxicity, R-717 is confined in a ventilated machinery room and R-717 systems are always designed with secondary loops at each temperature level. Several large supermarkets operate with R-717 especially in Luxembourg and Switzerland. R-717 can be used in indirect systems at the medium-temperature level, cascaded together with R-744 at the low-temperature level. Research into low-charge R-717 systems are also underway and can lead to breakthroughs in the future. R-744 The real breakthroughs using R-744 as a refrigerant began around 2005 with two major new options: R-744 as the only refrigerant in booster systems and R-744 in cascade with HFCs or other refrigerants. For using R-744 as the only refrigerant in small, medium and large size supermarkets, R-744 has been introduced in transcritical booster systems (Figure 4-2). So far, more than 18.000 transcritical R-744 systems of different sizes have been installed, mainly in Europe (73%) (Skacanova, 2018). Due to the widespread use of R-744 in Europe and Japan, the cost of systems has been significantly reduced and they now compete with HFC systems. In cascade systems, R-744 operates only at the low-temperature level. The medium-temperature compressor rack works with HFC-134a or R-717. Level of training and preferences of the contractor may influence the choice between transcritical R-744 and a cascade system. Basic R-744 transcritical booster systems without design enhancements to improve performance are less efficient than HFC systems at ambient temperatures above 26°C, but methods such as mechanical subcooling, ejectors, vapour injection, and parallel compression, for example, are being used to improve performance. These concepts enable energy efficient operation also at higher ambient temperature conditions, and numerous systems have been implemented lately in hot climates (Hafner, 2018). Low-GWP HFCs and HFC/HFO blends for R-404A and HCFC-22 replacement The AHRI/AREP Report # 21 (Shrestha, 2013) presents several low-GWP HFC/HFO blends (from 220 to 300) proposed to replace R-404A in condensing units that are the same as those proposed for centralised systems. The refrigeration capacities of these blends are slightly lower, energy efficiency slightly higher and temperature glides of 4 to 7 K are larger compared to R- 404A. Several of the blends exhibit temperature glide and it is important to follow manufacturer recommendations for installing, commissioning and servicing systems when using refrigerants with glide. 2018 TOC Refrigeration, A/C and Heat Pumps Assessment Report 87PDF Image | Heat Pumps Technical Options
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