Conference Agenda

The strategy for tackling the challenges of high ambient temperatures in transcritical CO₂ refrigeration systems design must be innovative and multi-dimensional. In 2023 an innovative system featuring a pressure exchanger has been introduced in the market: it partially recovers the mechanical energy lost through the transcritical expansion valve to create additional free subcooling, while bolstering the performance and resilience of CO₂ refrigeration systems in hot climate. Together with other systems, this technology is tailored to reduce energy consumption year-round and ensure reliable operation under higher ambient temperatures. The present paper reports the ultimate experimental results of a pressure exchanger integrated in a real installation as part of a demonstration activity within the EU-funded ENOUGH project. The installation, located in Hungary, showed efficiency gain of 15% on average compared to standard booster systems, with temperatures higher than 20°C, and allowing a reliable and more efficient operation up to 45°C.

Extreme temperature conditions are becoming frequent also in temperate areas. While carbon dioxide is spreading all over the world, as a safe and environmentally friendly refrigerant, there is an increasing need for making CO2 cycle efficient also under high ambient temperature, while assuring affordability, serviceability and cost competitiveness.
The Plank transcritical cycle involves heat rejection at two different pressure levels: heat is first rejected at a pressure lower than the optimal one of corresponding simple cycle, thus resulting in reduced compression ratio, then pressure is increased by a pump, to meet the optimal rejection pressure as required by the secondary fluid thermal flow capacity.
In this paper, thermodynamic analysis of a CO2 refrigeration cycle identifies optimal heat rejection pressures under extreme ambient temperature. By numerical simulations the practical implementation of the cycle is critically discussed, considering finite heat rejection exchange areas. Considerations related to the relative sizing of the two gas coolers and comparison with simple compression cycle are presented.

Over the years typical refrigeration system design temperatures have risen from 28°C to 35°C. It is expected that peak temperatures in the future will regularly exceed 40°C. New refrigeration systems will need to be designed for the expected peak temperatures. Whilst refrigeration system energy efficiency may increase at times at peak temperatures, there is a great opportunity to use the peak temperature designs to improve energy efficiency all year round.

Forward thinking designers must navigate through issues of rising temperatures and the goal to achieve Net Zero by 2050. This paper aim is to focus on the design of new refrigeration equipment that will be in operation for decades to come. It will consider how improving the overall refrigeration system energy efficiency may help offset the rising peak temperatures.

In this work a novel technology to adapt transcritical R744 supermarket refrigeration systems to warm and hot climates as well as to rising temperatures was proposed and exhaustively investigated. The novel solution consisted of a booster device (increasing the transcritical fluid R744 pressure) followed by an air-cooled gas cooler and located between the conventional air-cooled condenser/gas cooler and high-pressure expansion valve. The results obtained revealed energy savings by from 2.31 % to 2.91 % in Seville (Spain) and from 4.64 % to 5.73 % in New Delhi (India). To further increase the energy benefits from the proposed technology, the use of an expander replacing the high-pressure expansion valve was also considered. As a consequence, energy savings by 7.80 % in Seville and 14.44 % in New Delhi with an additional investment recovery time of about 3 years in both of the selected locations were assessed.