Pushing the CO2 equator further south

Many of the technical case study presentations throughout the ATMOsphere Europe 2013 conference demonstrated fruitful R&D efforts to improve the efficiency of CO₂-only refrigeration systems at higher ambient temperatures. Presentations by major CO₂ suppliers, including Carrier Commercial Refrigeration, Advansor and SCM Frigo, all indicated promising results with the use of parallel compression, ejectors and mechanical subcoolers, technology innovations used by the indus

Retailers call for CO₂ solutions for warmer climates

During the Second day’s Retail Panel, Amed Hafez, Equipment Manager for Modelo Continente Hipermercados (part of the Portuguese SONAE Group) that are now trialling their first hybrid CO₂/R134a cascade system, asked industry how confident they were that efficient CO₂ transcritical solutions for warm climates would be developed, and asked what the expected energy consumption of such systems would be compared to hybrid CO₂/R134a systems.

To answer his question, industry representatives spoke of the extensive R&D efforts underway to remove the so-called “CO₂-equator” presented by leading CO₂ system suppliers.

Promising initial results for CO₂ transcritical in warm climates using mechanical subcoolers

Lothar Serwas, Manager CO2OLtec Sales, presented Carrier’s efforts in developing the next generation of CO₂ DX systems for warm climates. For this, a number of innovations have been proposed and installed throughout Europe. These include:

Economizers: installed in Germany, Switzerland, Italy and Spain
Mechanical subcoolers: the first hydrocarbon mechanical subcooler has been installed in Spain, with two more planned
Ejectors: currently being lab tested in Carrier’s R&D centre, and for which field trial are planned in the coming year
Expanders: have also been modelled, but not yet been further investigated due to other more promising solutions

Successful field trial with CO₂ transcritical booster in Spain

Data from the field trial of their CO₂ transcritical booster and roof-top mounted hydrocarbon mechanical subcooler installation in Spain showed measured energy consumption is equal to HFC systems in southern European climates. The installation, which has an MT refrigeration capacity of 310 kW, has been operating successfully for one year in a supermarket in the Northwest of Spain, also showed that the CO₂ MT rack gains more than 30% in capacity, that the installed cost €/kW MT is equal to existing CO₂ range and the serviceability is equal to established CO₂ technologies. What is more, an electrical power saving of 14% can be achieved at an ambient temperature of 38°C.

Warm climate solutions in the form of high pressure subcoolers and parallel compression

According to Torben Hansen, Advansor is working on warm climate solutions for central European countries such as Romania, and is developing high pressure subcoolers: “Our experiences are not in the Iberian Peninsula, but in the US, where we also had 44°C this summer, and in Central European climates where temperatures reach 40°C, and we are very confident that we get efficient operation.” These systems involve the addition of a heat exchanger to get more sub-cooling, connected to a chilled water system, which is improves efficiency in comparison to having to compress CO₂ from -7°C. Other warm climate solutions proposed include removing flash gas by parallel compression, and water spray adiabatic systems, which also help to reduce flash gas.

CO₂ pump circulation system efficient in high temperatures

Mirko Bernabei from SCM Frigo also referred in his presentation to the company’s development efforts to widen the application range of CO₂ systems to warm climates. One of the applications SCM Frigo have developed is a CO₂ pump circulation system for MT, with and direct expansion LT, featuring the possibility to use CO₂ or NH3 for condensation. The CO₂ pump circulation system is easy to manage, is efficient and is also more efficient in high temperature climates. “CO₂ is a reality for the European retail market, and the technology will continue to improve,” Bernabei concluded his presentation.