Efficient R744 technology for supermarket heating, cooling and refrigeration - a theoretical assessment of energy advantages in various Spanish cities

Abstract

Various appealing expedients aimed at enhancing the energy efficiency of transcritical CO2 (R744) supermarket refrigerating systems have been recently developed. The concurrent adoption of these could lead such hydrofluorocarbon (HFC)-free technologies to become standard even in the South of Europe. Consequently, these solutions have drawn an enormous interest in the Spanish food retail industry as this features very severe regulations with the purpose of substantially mitigating ongoing climate change. In this theoretical work the performance of a state-of-the-art transcritical R744 supermarket refrigerating system, i.e. a solution including medium (MT) and low temperature (LT) overfed evaporators, parallel (or auxiliary) compression and “all-in-one” (or fully integrated) concept, was exhaustively investigated. This was compared to that of a baseline (i.e. “old” solution relying on R404A-based units to satisfy the refrigeration loads and a R410A reversible heat pumping unit) and to that of another alternative complying with the environmental legislative acts in force (i.e. solution based on a R134a/R744 cascade arrangement to provide the refrigeration demands and a R1234ze(E) reversible heat pump unit). The study was carried out by considering an average-size food retail store located in the Spanish climate context. The outcomes obtained revealed that the fully integrated R744 refrigeration plant offers total energy conservations between 1% (in Tenerife) and 33% (in Burgos) over conventional separated HFC-based units. In addition, the investigated transcritical R744 system brought the total annual electricity consumption down by at least 39% compared to HFC-based arrangements in heating mode.