The study evaluates the performance of two medium-sized supermarkets, R1234ze(E)/CO₂ cascade system and CO₂ transcritical system, started operating in 2023 located in northern Italy. Both supermarkets feature two stages, medium-temperature (MT) and low-temperature (LT) that provide cooling to MT and LT cabinets. The primary objective of the study is to assess the efficiency of the refrigeration system based on field measurement. Since both systems provide heat recovery when it is required, it is essential to analyses how the coefficient of performance (COP) of each stage is affected by the heat recovery operation, independently of the benefits derived from the recovered heat. To achieve this, field measurement data were gathered at one-minute intervals throughout a year. Models were developed in MATLAB for both supermarkets using REFPROP. The required calculations are explained in detail, average cooling demands, evaporation temperatures, internal superheating at each stage are discussed and COP was calculated. The field measurement of electrical consumption of the entire component systems permitted a comprehensive study into the electrical consumption of refrigeration systems, heating, and cooling. The results show that the R1234ze(E)/CO₂ cascade system in comparison to CO₂ transcritical has higher efficiency at MT stage when the ambient temperature exceeds 20 °C, and at LT stage when the ambient temperature is above 16 °C. COP in ambient temperature lower than 20 °C is influenced by different heat recovery operation in these two systems. R1234ze(E)/CO₂ cascade system frequently operates at higher fixed condensation pressures to meet heat recovery needs in ambient temperature interval, leading to more consistent COP of MT during this period. In contrast, the COP of the CO₂ transcritical system in MT varies as it operates in both transcritical and subcritical modes to meet the heat demand. The heat recovery analysis and its efficiency are presented in Part II of this article.

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 degrees 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 degrees C and 9 degrees 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.

Supermarket refrigeration systems offer the possibility to recover significant amounts of energy. These amounts may at times be higher than what the supermarket needs. In these cases, export of heat or air conditioning to neighboring buildings is a solution for increased overall energy efficiency. However, although previous studies have demonstrated the technical viability of such systems, they are rarely implemented in practice. In this work, possible barriers to and drivers of implementation of thermal energy export from supermarkets are investigated. The empirical work consists of a mixed-method data collection and in-depth analysis of six case studies of supermarkets that are in a research collaboration project between the KTH Royal Institute of Technology in Stockholm and CIT Energy Management in Gothenburg, Sweden. The main findings indicate that several barriers, especially the split economic incentives of supermarkets and property owners and a lack of information, have significant detrimental effects on the uptake of thermal energy export solutions. Cooperative agreements between supermarkets and property owners are found to have the greatest possibility to mitigate the impact of the barriers, but standardized templates are needed to reduce their associated legal, technical, and administrative uncertainties.

Overfeeding the medium temperature level evaporators using liquid ejectors is one of the features of the modern CO2 refrigeration systems for supermarket applications, which provides higher evaporation temperature. The liquid leaving the evaporator is accumulated in a liquid receiver before the compressor and is pumped back to the main receiver before the evaporators by the liquid ejector. This paper uses field measurements of two supermarkets in Sweden. One of the supermarkets is analysed in two days where it operates under overfeed conditions at one day and under dry expansion conditions at the other, providing better understanding of the benefit of overfeeding the cabinets. The first system shows that the evaporation temperature is increased by 2 K (from -6 degrees C to -4 degrees C) while the air set point temperature inside the cabinet is kept satisfied. The second system shows that the evaporation temperature can be up to -2.5 degrees C with a small impact in the cabinets' air set point temperature satisfaction.

This study explores the capability of a supermarket to fulfill the thermal demands of neighboring buildings. The research combines field measurements analysis, obtained from a Swedish supermarket which covers the neighbors' thermal demands, with theoretical calculations, using thermodynamic models of the refrigeration system and the ground source thermal storage. In contrast to previous studies, this work is unique in its use of demonstrating a real-life built case study rather than only theoretical approach. Results demonstrate that inte-grating ground source storage in a supermarket can meet the thermal demands of neighboring buildings without requiring additional equipment. The refrigeration system accounts for 80% of the total heat demand, while the ground serves as a heat source for the rest. This approach results in 67% annual operating cost savings for the neighboring buildings. In addition, ground source subcooling provides 9% annual energy savings to supermar-ket's refrigeration system. By exporting heat to neighboring buildings, the proposed solution emits 90% less CO2 in Uppsala and 67% less in Stockholm compared to solutions in which the refrigeration system only meets the refrigeration demands. Summing up, the concept of utilizing supermarkets to meet thermal demands offers a more energy-efficient operation for both supermarkets and property owners while significantly reducing annual energy consumption and emissions.

This paper presents the performance analysis of a well-instrumented supermarket in Sweden where heating, air conditioning and ground storage are integrated into a booster trans-critical CO2 refrigeration system. The supermarket has applied several features of a state-of-the-art system, including overfeed evaporators, 2-stage heat recovery, and air conditioning. Two warm and two cold days operation are used for the control and the performance investigation. The heat recovery follows the theoretical control strategy, where the setpoint temperature for the discharge pressure is the forward water temperature to the heating system. The combination of low water temperature return from the space heating system and 2-stage heat recovery provides efficient operation; COP heating is estimated around 6. The warm days study shows that importance of fast fault detection which resulted in 16% energy savings in this case study. The fault drives to limitation of the air conditioning capacity and as result indoor temperature increment. The air conditioning COP is estimated around 2.5 for both warm days, with potential of 20% increase in the COP with optimized operation without thermal leakage to the ground.

This paper investigates ellipsoid-shaped macro-encapsulated phase change material (PCM) on a component scale. The selected PCM is a paraffin-based commercial material, namely ATP60; differential scanning calorimetry and transient plane source method are used to measure ATP60's thermo-physical properties. A 0.382 m(3) latent heat thermal energy storage (LHTES) component has been built and experimentally characterized. The temperature measurement results indicate that a thermocline was retained in the packed bed region during charging/discharging processes. The experimental characterization shows that increasing the temperature difference between the heat transfer fluid (HTF) inlet temperature and phase-change temperature by 20 K can shorten the completion time of discharge by 65%, and increasing HTF inlet flowrate from 0.15 m(3)/h (Re = 77) to 0.5 m(3)/h (Re = 256) can shorten the completion time of charge by 51%. Furthermore, a one-dimensional packed bed model using source-based enthalpy method was developed and validated by comparison to experimental results, showing discrepancies in the accumulated storage capacity within 6.6% between simulation and experiment when the Reynolds number of the HTF inlet flow ranges between 90 and 922. Compared with a conventional capsule shaped in 69-mm-diameter and 750-mm-long cylinders, the ellipsoidal capsule shows 60% less completion time of discharge but 23% lower storage capacity. Overall, this work demonstrates a combined experimental and numerical characterization approach for applying novel macro-encapsulated PCM geometries for heating-oriented LHTES.

Heat recovery from local resources is shown to be a promising solution to reduce the carbon footprint of district heating. Supermarkets equipped with a CO2 refrigeration system and a geothermal storage offer a larger heating capacity, compared to traditional solutions. While district heat could benefit from this higher heat recovery availability, supermarkets could generate an income from a capacity that would be otherwise unused. For the first time, this study applies a detailed modelling approach considering both sides of such a synergy. The objective is to assess the techno-economic and environmental impact of a coordinated control strategy. Since the heat recovery from the supermarket consumes additional electricity, power-to-heat is implemented as a solution to reduce the overall CO2 emissions. This is demonstrated by scenarios simulated for a district in Stockholm. Hourly electricity CO2 intensity and prices are implemented as signals to prioritize either the district heating central supply or heat recovery. By boosting the use of electricity when cleaner, a CO2 intensity-driven control show the potential of reducing the carbon footprint of the district (−9.4%). A control based on prices, instead, is more convenient economically both for the district (−1.4% heat cost) and for the supermarket (−32% operational cost).

Integrating latent heat thermal energy storage (LHTES) units into building heating systems has been increasinglyinvestigated as a heat load management technology. A conventional LHTES integration method for heat pumpbased heating systems is to connect the heat pump’s condenser for charging the LHTES unit. This integratinglayout however usually leads to increased electricity input to the heating system. To underline this issue andprovide solutions, this paper presents three new LHTES integrating layouts where the LHTES unit is connectedwith the de-superheater of the main heat pump (Case 2), the condenser of a cascaded booster heat pump cycle(Case 3), or a combination of using both the de-superheater and the booster cycle (Case 4). In the context of amulti-family house in Stockholm, a quasi-steady state heating system model was developed to evaluate the newintegrating layouts, which were benchmarked against the baseline heating system without storage (Case 0) andthe conventional integrating layout using the main heat pump condenser (Case 1). Hourly electric power input tothe heating system was modelled for calculating the performance indicators including the heating performancefactor, the operational expense and justifiable capital expense, and the indirect CO2 emissions. Two load shiftingstrategies were simulated for an evaluation period of Week 1, 2019: 1) charge during off-peak hours (8 pm to 6am) and 2) charge during daytime hours (10 am to 7 pm). The simulation results of the off-peak charging strategyshow that, in Cases 2–4, the heating performance factor is 22%-26% higher than Case 1 and the operational expense can be reduced by 2%-5% as compared with Case 0. The savings in the operational expense can justifythe capital expense of 11 k-25 k Swedish Krona (SEK) for the LHTES systems in Cases 2–4 assuming a 15-yearoperation. Furthermore, the advantage of using the daytime charging strategy is principally the mitigation of CO2 emissions, which is up to 14% lower than the off-peak charging strategy. In summary, higher energy efficiencyfor heating is validated in the three new proposed integration layouts (Cases 2–4) against the condensercharging layout.

This paper investigates the opportunity of utilizing the spare heating capacity of CO2 refrigeration systems in supermarkets to produce heat to be sold to district heating network operators. A comprehensive description and assessment of two control strategies that could be implemented to enable the heat export function are presented. To maximise the heating capacity during the coldest moments of the year, the integration of geothermal storage with the CO2 system was investigated as an additional scenario. The BIN method was used to perform annual energy calculations. Furthermore, a sensitivity analysis was carried out on the most critical parameters, namely the heating demand, price ratio and temperature levels of the district heating network. For the assumed prices and energy demands, the supermarket could make profits corresponding to up to 16% (10,000 (sic)/year) of the annual energy cost by selling part of the heat recovered to the district heating network operator. Furthermore, the heat exported could save up to 18% of the annual CO2 emissions of the supermarket compared to the baseline. Finally, the sensitivity analysis showed that the economics of this solution is the more profitable, the lower return temperature of the heating network where the installation is connected.