Conference Agenda

Ultra-low temperature (ULT) freezers maintain storage temperatures of -50°C to -86°C in ambient conditions ranging from 16°C to 32°C. Freezers with cascade refrigeration systems have been used for decades to preserve cultures, vaccines, samples, specimens, and viruses. Typically, these ULT freezers are stand-alone units, and large institutions operate freezer farms containing hundreds of freezers. Climate change has contributed to an increase in average global temperatures and more frequent high-temperature extremes, such as heatwaves. This paper examined the impact of rising temperatures on ULT freezers. Three key changes were identified: a decrease in efficiency, an increase in heat load, and an increase in component operating temperatures. These changes were investigated using a 400-litre freezer, which maintained a storage temperature of -85°C at ambient temperatures of 20°C and 33°C. The evaluation included the power profile, the pressures for both stages, and the temperature in the compressor compartment.

Rising ambient temperatures significantly impact the thermodynamic performance of transcritical CO₂ refrigeration systems. To investigate these effects, detailed mathematical modelling of the gas cooler was developed and integrated into a CO₂ refrigeration system model. The thermodynamic performance was investigated in the broad range of ambient temperature between 25 ^oC and 40 ^oC, and high-side CO₂ pressure from 75 bar to 140 bar. The results of COP and cooling capacity show a significant decrease with increasing ambient temperature. To improve the performance of CO₂ refrigeration systems at high ambient temperatures evaporative or spray cooling can be employed to enhance the heat transfer in the gas cooler and reduce gas cooler temperature and pressure. In this paper experimental and modelling results are used to investigate the impact of spray cooling on the performance of CO₂ refrigeration systems at high ambient temperatures.

As global temperatures rise due to climate change, convenience stores face increasing challenges in maintaining optimal refrigeration and store temperatures. This study evaluates the impact of extreme heat on a small independent UK convenience store using an EnergyPlus™ model to simulate thermal dynamics during the UK July 2022 heatwave. The analysis examines air conditioning (A/C) performance, refrigeration efficiency, and indoor temperature stability under varying cooling capacities. Results show that if the A/C system was designed using EnergyPlus™ algorithms, there would be sufficient spare capacity, with the model predicting that the store temperature would stay stable even during outdoor peaks of 40.15°C. Sizing for a peak outdoor temperature of 27.7°C revealed that indoor temperatures exceeded the setpoint by 4.0°C. To enhance store resilience, strategies such as A/C sizing for higher peak temperatures are advised to adapt for future climate conditions.