Enex’s ejector technology

Solving the “CO2 equator” challenge: Enex’s ejector technology

Enex has been actively developing solutions to increase CO2 system efficiency in warm ambient climates like Spain and Italy. Using parallel compression and ejectors in unison, the company has realised significant efficiency gains and cost (first cost + energy cost) reductions.

At this year’s ATMOsphere Europe 2015, R744.com caught up with Sergio Girotto to find out more about the Italian manufacturer’s state-of the art technology.

This design solution for a widespread use of CO2 in refrigeration is ready and proven, after 2 years in development,”

Girotto.

Ejector technology: improving CO2 system efficiency

To address the fact that the maximum evaporation temperature is limited by the closing temperature gap between the air inlet temperature and refrigerant temperature at the evaporator outlet, in 2012 Enex developed its ejector liquid overfeeding technology. This allows the evaporation temperature to always be the maximum allowed by the thermal load, enabling significant energy savings even at the high outdoor temperatures found in southern Europe.

The measured energy consumption from Enex’s liquid ejector installations confirms laboratory measurements: savings of between 10% and 15% only as a result of improved evaporator feeding.

Immediately after the first installation of liquid ejectors, in 2012, it became clear that there was another possibility: using gas ejectors as a “help” for auxiliary compressors. Thanks to the cooperation with Frigo-Consulting and Alpiq the improved design became reality in 2013 in one installation in Bulle (Fribourg region). Further improvements were introduced in some other installations in 2014. Now the complete solution is called “multijet”, even if it is a combination of several improvements,”

Girotto.

Multijet ejector solution saves up to 30%

According to Girotto, Enex’s “full saving” CO2 system, which features ejectors, can reduce energy consumption by 25% to 30% compared to a standard CO2 solution, thanks to a combination of:

  • Evaporator overfeeding: achieves energy savings of 13-15% when combined with an optimal control logic for suction pressure
  • Auxiliary compressors, for flash vapour re-compression: achieves energy savings of 15% on a typical summer day in southern Italy
  • Pre-compression with ejectors: reduce the mass flow faction managed by the main compressors, thereby maximising the benefits of auxiliary compressors, especially in warm ambient climates

While the initial cost of the Multijet ejector solution is higher than a R404A system, the lifetime cost is significantly lower, as revealed by a cost comparison between a standard CO2 refrigeration system, a multijet CO2 solution, a R404A solution and a solution with mechanical sub cooling.

The positive performance of Enex systems using liquid and gas ejectors at operational test sites has also been noted by Danfoss’ Funder-Kristensen in a presentation at ATMOsphere Europe.

Improvements to system reliability and ease of service

In addition to system efficiency the overfeeding design makes the refrigeration system more robust, as it avoids the “nightmare” of liquid suction to compressors, which is the most frequent cause of compressor breakdown.

About Enex

Enex has more than 10 years experience in applications using CO2. The company has produced more than 500 large size CO2 transcritical refrigeration units and several CO2 heat pumps for the most demanding markets and climatic conditions. Today, Enex dedicates many of its resources to research and development, having established fruitful relationships with universities and research organisations, which have led to significant innovations in the field.

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