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present work it is assumed that the real ejector efficiency (ππejec) is known, which means that the pressure ππ8 can be found by solving: ππejec β ππ(ππ8,ππ)=0, (7) using the built-in MATLAB function fzero, which combines bisection, secant, and inverse quadratic interpolation methods. Ejector efficiencies up to 34 % are modelled in the sensitivity study, while a 25 % ejector efficiency is used as base case (see Table 2). This is based on the ejector study of CO2 heat pumps by Banasiak et al. (2012), who measured experimental ejector efficiencies in the range 23 % to 31 %, and simulated values of up to 34 %. Ejector technology can also be applied in R410A systems, e.g. as studied by Pottker and Hrnjak (2015), who measured ejector efficiency between 12 % and 20 %. 2.1.2 Compressor Performance Modelling ππcomp,is h3,isβh2 ππ==, Compressor performance is calculated using isentropic efficiency, which is defined as: ππc o m p h 3 β h 2 where ππcomp,is is an isentropic compression process from point 2 to pressure ππ3. Figure 5 shows comp (8) efficiency and operating range data for the CO2-based Dorin CD1000H compressor, which is based on compressor inlet pressure (ππ ), inlet temperature (ππ ), and outlet pressure (ππ ), as explained in detail 223 a vendor model for the Dorin CD1000H compressor (Wolf, 2015), where efficiency is calculated from by Brodal et al. (2018). This compressor operates with efficiencies between 67 % and 71 % for ππ = 0 Β°C in a transcritical cycle (i.e. over pcrit), even if ππ is shifted a few degrees, e.g. by evap@p2 evap@p2 an ejector. Figure 6 shows the isentropic efficiency for six additional compressors, and was calculated using data obtained from online software from Bitzer and GEA. Figure 5. Isentropic efficiency of the CO2-based CD1000H compressor, assuming 10 K superheating. 7PDF Image | CO2 Heat Pump Performance
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