Comparative analysis of HFO-CO₂ cascade vs CO₂ transcritical refrigeration systems in two supermarkets. Part II: Evaluation of heat recovery and integration of heat pumps based on field measurements

This study examines heat recovery from refrigeration systems and the operational benefits of integrating heat recovery in two medium-sized supermarkets in northern Italy based on field measurements. A supermarket operates with a R1234ze/CO₂ cascade system, which is integrated with heat pumps, and the other is a CO₂ transcritical system. The system description, along with the processes of data collection and validation, is discussed in detail in part Ⅰ of the article. Both systems are equipped with heat recovery and began operating in 2023. The floating condensation model was developed in MATLAB, utilizing REFPROP to calculate the coefficient of performance (COP) of heat recovery. Furthermore, the COP of heat pumps and the COP of each stage in floating condensation mode are calculated. Results show R1234ze/CO₂ cascade system integrated with a heat pump and air conditioning fully meets the cooling and heating demands of the supermarket's sales area, by using 12 % more annual electricity compared to the floating condensation mode. The continuous heat recovery in the R1234ze/CO₂ cascade system leads to a higher amount of heat recovery compared to the CO₂ transcritical system. The heat recovery of the CO₂ transcritical system is not used as a main source to cover the heat demand. In this system, due to lower heat demand, heat recovery most often occurs in subcritical mode, and it does not fully utilise its heat recovery potential. Only 39 % of the total heat recovered occurs in transcritical mode, with the remaining heat rejected to the air. COP of heat recovery of this system is higher than the cascade system; however, the values in both systems for ambient temperature lower than 4 °C are comparable. Furthermore, the results show that in floating condensation mode, the COP of the CO₂ transcritical system in the MT and LT stages is higher than the cascade system at temperatures below 16 °C and 9 °C, respectively, this trend reverses at temperatures above these values. The global COP of the cascade system consistently remains higher than that of the CO₂ system.