Integration of a cold thermal energy storage for air conditioning demand in a CO2 refrigeration system of a supermarket

There is a significant transition in supermarket refrigeration, with a strong focus on reducing energy demand and installation costs. Generally, industry processes require cooling the most for short periods every day. The rest of the time, the cooling system runs at partial load with lower efficiency, but it is still designed for the highest capacity. Applying cold thermal energy storage (CTES) technologies, which can deliver some of the cooling during peak times, will reduce peak load demand and will allow for load shifting to periods with low electricity cost, free cooling capacity from the rack or high electricity production from renewable energy sources (e.g. photovoltaic panels). This will also contribute to a more flexible power system, and allow for an increased proportion of power production with variable renewable energy sources. Additionally, these units can also lead to a significant downsizing of the compressor pack, reducing the cooling system capacity. Currently, the air conditioning (AC) in REMA 1000 supermarkets, a leading supermarket chain in Norway, is supplied by a glycol circuit which is cooled by the CO2 (R744) booster refrigeration system. The design capacity of the refrigeration unit must handle all the refrigeration loads and the AC load during the warmest summer day, which results in overcapacity and part load operation for most of the year. This master’s thesis describes and investigates a proposed design for the implementation of a CTES dedicated to AC demand in a supermarket located in the Oslo region. This system aims to substitute the existing glycol circuit towards the air handling unit (AHU). Simulation results demonstrate that CTES offers substantial potential for reducing electrical peak power consumption during the warmest periods. The functioning of the CTES and its impact on the existing refrigeration system were simulated, revealing a peak reduction of up to 32,33%. The load shifting capability is demonstrated, absorbing 31,53% of the daily electricity consumption during the night, when the supermarket is closed, compared to 16,14% considering the instantaneous production of AC with the existing system. Consequently, electricity consumption can be increased by up to 74,8% during the night and decreased by up to 28% during the day. Even though energy savings are not the primary objective of this project, they are achieved by producing and storing energy required for AC during periods when the outdoor temperature is lower, and the coefficient of performance (COP) of the system is higher. The energy savings can reach up to 11,8% during the hottest day. Finally, the economic benefits of the system are assessed under spot pricing and tariff pricing systems, revealing potential electricity cost savings of up to 12,56% and 16,45%, respectively. The main big challenges of this system still remain its economical viability, in terms of payback time, and expanding its utilization during the winter period.