In hot climates a “novel technology” could reduce the energy consumption of commercial CO2 (R744) refrigeration systems by up to 14% compared to standard setups, according to new research from the University of Southern Denmark (USD).
The concept integrates a pressure booster device and an air-cooled gas cooler installed behind the existing heat rejection component and replaces the high-pressure expansion valve with an expander. Modeling demonstrated potential energy savings compared to conventional CO2 systems in Seville, Spain, and New Delhi, India. In Seville, average summer highs are between 35 and 40°C (95–104°F), and in New Delhi they frequently exceed 44°C (111.2°F).
The findings were presented by Guruchethan Matha, a postdoctoral researcher at USD, at the International Institute for Refrigeration (IIR)’s inaugural International Conference on Refrigeration Adapting to Rising Temperatures (Adaptation 2025). The event, hosted by the Institute of Refrigeration UK, was held August 10–13 in Manchester, England.
“The combined solution results in an energy savings of 7.8% in Seville and 14.4% in New Delhi with a return on investment [ROI] of roughly three years in both locations,” Matha said.
The design: The researchers broke the design into two stages. First, they installed the booster device followed by an additional air-cooled cooler between the outlet of the air-cooled condenser or gas cooler and the inlet of the high-pressure expansion valve. Then they replaced the high-pressure expansion valve with an expander.
- The booster device, which Matha related to a pump, slightly increases the refrigerant’s pressure with “less electricity” than a parallel compressor, with the air-cooled cooler returning the temperature to the previous outlet. The design reduces refrigerant vapor content and minimizes flash gas formation, lowering compressor load.
- Although the technology offers a “cheap” solution compared to other subcooling techniques, it provides only a “marginal” energy savings, according to Matha, with a 2.3‒2.9% reduction in Seville and a 4.6‒5.7% reduction in New Delhi.
- However, including the replacement of the high-pressure expansion valve with an expander, which Matha related to turbine technology, allows the recovery of energy and increases the COP by 8.5% at an ambient temperature of 23°C (73.4°F) and by 22.5% at 40°C.
Modeling loads: The parameters used by the researchers for the comparison included a low-temperature (LT) load of 35kW (10TR) at −32°C (−25.6°F) and a varying medium-temperature (MT) load, based on the ambient conditions, of around 100kW (28.4TR) at −8°C (17.6°F).
Economic assessment: Both the booster device and the expander are under development. Industry manufacturers provided cost estimates of the equipment, including €15,600 ($18,300) for the booster device, €9,000 ($10,600) for the expander and €7,000 ($8,200) for the air-cooled gas cooler.
- “If the booster device operates with a 50% efficiency, it will take nearly 10 years for the return on the investment,” Matha said, adding that, at 65% efficiency, it will take eight years.
- Adding the expander to recover energy cuts the ROI to three years based on operation with a 65% efficiency.
Quotable: “To further open the doors to supermarket [CO2] applications in warm and hot climates, the literature highlights the need for simpler and more affordable technologies to enhance the performance of transcritical R744 refrigeration systems,” Matha said. “[Our] proposed technology requires relatively few additions with off-the-shelf standard components.”
“The combined solution results in an energy savings of 7.8% in Seville and 14.4% in New Delhi with a return on investment [ROI] of roughly three years in both locations.”
Guruchethan Matha, a postdoctoral researcher at USD
