Abstract
• Design of a novel cold thermal energy storage unit for CO 2 refrigeration systems. • Investigation of the charging and discharging performance of the unit. • Variation of the heat exchanger geometry to adapt to different refrigeration load. • Condensation and evaporation temperature of CO 2 are the most critical parameters. • Maximum discharged energy is 35.29 kWh over 4.5 h with a mean rate of 7.90 kW. Cold Thermal Energy Storage (CTES) technology can be introduced to refrigeration systems for air conditioning and process cooling to reduce the peak power consumption by decoupling the supply and demand of refrigeration. In these systems, the refrigeration demand can vary significantly over a day, resulting in a challenging peak and valley load pattern on the electrical grid. This paper presents the design, development, and experimental performance investigations of a novel plates-in-tank CTES unit design intended for integration into pump-circulated CO 2 industrial refrigeration systems. The CTES unit is composed of a stainless steel container filled with water as the latent storage medium and fitted with a pillow plate heat exchanger. The refrigerant (CO 2 ) circulates within the heat exchanger to transfer heat with the storage medium. The current study demonstrates the feasibility of implementing a latent CTES unit directly into the primary refrigerant circuit for peak shaving of the refrigeration load. The results show that the evaporation and condensation temperatures of the refrigerant are the most critical parameters influencing the performance of the charging and discharging cycles, respectively. The unit demonstrated a mean discharge rate of 7.90 kW over a total discharging cycle time of approximately 4.5 h. The resulting maximum discharged energy was calculated to 35.29 kWh.
Highlights
The demand for electricity in modern society is high
Thermal Energy Storage (TES) can represent one solution, as it allows for peak shaving of the thermal demand, ranging from several cycles per day to a seasonal timescale depending on the application [7]
The results have shown that integrating the Phase Change Material (PCM)-Heat Exchanger (HEX) as a subcooler downstream the condenser could increase the Coefficient Of Performance (COP) by 8% in UK climate conditions
Summary
The demand for electricity in modern society is high. The peak and valley consumption pattern that is dominating today is a challenge for the grid. With the current growth in the air-conditioning market, the IEA predicts that over 40% of the total peak power demand in hot climates will be caused by space cooling in 2050 [6]. CTES integrated into Air-Conditioning (AC) systems for buildings have shown good performance by enabling peak shifting of up to 100% of the cooling load to off-peak hours depending on system design [8]. This approach has been popular for commercial buildings occupied only during working hours, which causes a substantial difference in the peak and off-peak cooling load [9]. Latent heat storage provides high energy density storage, a tailored phase change temperature and a near-constant stor age temperature during the charging and discharging processes [10]
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