Abstract

This study introduces an improved methodology to evaluate with accuracy the performance of a conventional system with R404A and a Booster system with R744. Reciprocating and scroll compressors are modeled with improved semi-empirical approaches, and their operation is ideally controlled to maintain the required refrigerant mass flow rate with an On/Off and variable speed control system. The R744 gas cooler is modeled with a four-zones model and the R404A condenser with a three-zones model. The R744 condenser is modeled with the superheated zone discretized into eight zones to avoid unrealistic results due to the variation of its thermo-physical properties and the two-phase and subcooled zones with one zone respectively. In line with the design, the Booster condenser enters into the pseudo-critical zone at an ambient temperature of 23 degrees C, while the gas cooler is activated after 31 degrees C. The compressor models present errors lower than 10%, while the Booster model presents mean deviations lower than 2.3%. The Booster system presents better COPs than the conventional at ambient temperatures lower than 15oC. At higher ambient temperatures, the COPs of both systems are similar: the conventional system overperforms the Booster up to 6%, being in disagree with the literature results where these differences increase up to 30%. The proposed methodology allows to reduce the overall model error by 3% with respect to a thermodynamic cycle-based model; allowing to improve the comparison between the Booster system with R744 and the conventional one with R404A, which leads to more transparent results than the reported common comparisons.