GL2018 highlights: CO2 systems now competitive in any climate
Among the 175 papers and keynotes presented at the 13th IIR-Gustav Lorentzen Conference on Natural Refrigerants on June 18-20, 2018 in Valencia, Spain, CO2 was the refrigerant which was most frequently the subject of study (93 papers), ahead of hydrocarbons (44 papers), ammonia (27 papers) and water (6 papers). 43 of the 93 studies on CO2 concerned commercial cooling, with an emphasis on transcritical CO2 systems and technical solutions which would improve the energy efficiency of these systems, especially in hot countries.
According to Shecco1, CO2 transcritical technology is gradually gaining ground in different parts of the world. By March 2018, the total number of installed CO2 transcritical refrigeration systems was about 17,800, including 14,000 in Europe, 3,100 in Japan, 340 in the USA, 210 in Canada and 102 in South Africa. Such systems are also installed in Australia (20), Indonesia (13), Argentina (7), Chile (4), Brazil (3), Taiwan (2), China (1), Jordan (1) and Columbia (1). The total amount is expected to reach 27,000 by 2020 and 81,000 by 2030.
K. B. Madsen and E. E. Kriezi2 used a simulation tool to investigate the impact of add-on ejector solutions on standard transcritical CO2 architecture, booster or parallel compression systems. Booster systems have been used in supermarkets on larger scale since 2007 and parallel compression systems since 2011. Currently, three ejector solutions are mainly used in installations: high pressure lift ejectors (HP ejector) as an add-on to parallel compression systems, low pressure lift ejectors (LP-ejector) as an add-on to booster systems, and liquid ejectors as an add-on to any system for supporting flooded operation of the evaporators.
The authors calculated the energy savings compared to a standard booster CO2 system and the payback times of the various add-on ejector solutions for 128 locations across the globe, taking into account the average annual temperature (between 0°C and 30°C) and the cooling capacity of the system (from 40 to 300 kW).
Finally, for warm climates with average annual temperature of 15°C and above, the HP ejector solution is economically beneficial; the payback is between 0.66 of a year (average annual temperature of 30°C and 300kW of cooling capacity) and 2.63 years (15°C; 75 kW ). The LP ejector solution has a slightly longer payback period.
For colder climates with average annual temperature between 0°C and 15°C, the most competitive solution is the liquid ejector with paybacks between 0.63 of a year (15°C; 300 kW) and 3.70 years (0°C; 40 kW). Though HP and LP solutions are providing significant energy savings compared to a standard booster system, they result in longer payback times.
In another study3, G. Pisano stresses that a supermarket located in Southern Italy, with peak temperatures of 45°C, could reduce energy consumption by almost 30% by switching from a “simple CO2 booster” configuration (A) to a “booster with parallel compression, liquid and vapor ejector” configuration (E). A return on investments (ROI) of only 2 years is obtained when comparing aggregated costs (capital + running costs) of configurations A and E.
In conclusion, the author observes that there are now more than 200 installations using parallel compression in conjunction with ejectors, making it possible to consider these fully mature and available technologies, and leading CO2-based refrigeration plants outperform HFC systems at any European latitude with reasonable return on capital investments.
1 Skacanová K., de Oña A., Gkizelis A. Global market and policy trends for CO2 and ammonia in refrigeration. In: 13th IIR-Gustav Lorentzen Conference on Natural Refrigerants, June 18-20, 2018, Valencia (Spain). Paris: IIF-IIR, 2018. Available in Fridoc.
Madsen K. B., Kriezi E. Financial aspects of ejector solutions in supermarket and smaller industrial systems. In: 13th IIR-Gustav Lorentzen Conference on Natural Refrigerants, June 18-20, 2018, Valencia (Spain). Paris: IIF-IIR, 2018. Available in Fridoc.
3 Pisano, G. The use of ejectors technology: how to boost efficiency in warm climates – a real example from Italy. In: 13th IIR-Gustav Lorentzen Conference on Natural Refrigerants, June 18-20, 2018, Valencia (Spain). Paris: IIF-IIR, 2018. Available in Fridoc.