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R404A direct expansion system (DX) and a R134a/R744 cascade system (C). In order to fully supply the 1 2 3 4 5 6 7 8 9 DHW and heating demands, two heat pumps (HPs) for DHW and heating are operated when DX and C systems are considered. Table 1 summarizes the configurations investigated. Table 1. Configurations considered 10 Acronym Configuration R744 Booster system with parallel compression and heat recovery for DHW System B with full Heat Recovery (DHW and space heating) System B and Heat Pump for space heating R404A Direct expansion system and Heat Pumps for DHW and space heating Cascade R134a/R744 system and Heat Pumps for DHW and space heating 11 12 13 14 15 B+ HPs 16 B BHR DX+ HPs C+HPs 17 18 19 20 21 22 23 24 25 The mathematical models of the refrigeration systems and of the heat pumps have been developed in the 26 3. MODEL DESCRIPTION TRNSYS environment (Klein et al., 2010), as it allows carrying on dynamic simulations of a complex 27 28 29 30 As an example, the heating and cooling demands of the supermarket are affected by the presence of open 31 system, which includes mutual interactions with the building and with the HVAC system. display cabinets and, in turn, their cooling load profile is strongly dependent on the indoor thermal and 32 33 34 35 display cabinets and the cold rooms in the food store have been modelled as described in Polzot et al. (2015); 36 humidity levels and on the ratio LT/MT refrigerating capacity (Mylona et al, 2018). Thus, the refrigerated the total cooling capacity at rated conditions of each display cabinet is adjusted taking into account realistic 37 38 39 40 41 42 43 44 45 46 47 48 49 3.1. Commercial refrigeration unit 50 and time-dependent working conditions in a supermarket. The influence of indoor air temperature and humidity on the sensible and latent fractions of the cooling load are considered as well as the time schedule for auxiliary devices (Cortella et al, 2011, Polzot et al. 2015). On the other hand the contributions due to the sensible and latent heat transfer by air infiltration from the open cabinets and to conductive and radiative heat transfer through both display cabinets and cold rooms contours are computed as credits to the HVAC system. Hereafter the models of the refrigeration systems and of the heat pumps are described. The simulations of the different commercial refrigeration systems are based on sub-hourly profiles of the 51 52 53 54 et al. (2015 and 2016c). The thermodynamic and thermophysical properties of the refrigerants are calculated 55 cooling load at the evaporators and of the outdoor temperature. A detailed description can be found in Polzot by linking our in-house routines in the Trnsys environment to the CoolProp libraries (Bell et al., 2014). 56 57 58 59 compressors (ratio of the theoretical compression work to the electrical power use) as a function of the 60 61 62 63 64 65 Correlations from the manufacturer (Bitzer, 2017) have been used to define the global efficiency of the pressure ratio. In detail, such correlations are (Polzot, 2017):PDF Image | R744 BOOSTER INTEGRATED SYSTEM
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