History of a New Technology - Part 4
Technical Evolution – Booster, Economizer, and Double Stage
Following the completion of the first “full-scale” plant, we implemented numerous systems across Denmark and Sweden, and a few in Italy. Between 2003 and early 2004, about twenty systems were built. These machines were derived from the experience gained with the Treviso plant: units with compressors in parallel, single-stage type for MT (medium temperature) and internal compound two-stage for LT (low temperature), featuring an “open flash tank” type receiver.
Meanwhile, one leader in commercial refrigeration, Linde Carrier, completed in 2004 its first plant in Wettingen, Switzerland. Although it was a relatively simple system—single-stage for MT and cascade for LT—it was of significant size. There were, in the Wettingen plant, some interesting steps forward: first of all the first Bitzer transcritical compressor, then the first electric valve - from industry - for controlling high pressure in gas cooler and the first gas cooler CO2-air from Luve.
The company Bock had already available a small trascritical “open type” compressor at prototype level, designed for testing air conditioning for bus for a german company.
It was clear at this point that, even if everything was still at “field test” stage, there were more players exploring the new technology, however still at an early stage.
1. The High Pressure control valve and Economizer: Optimizing Flash Gas
in 2006 Danfoss released some field test valves for high pressure control, that is the model ICMTS, derived from a valve from industrial refrigeration, together with a proper controller, EKC326. The new devices made it possible to apply a proper control of pressure in liquid receiver, different from the first systems with a floating intermediate pressure. Enex started experiments of an innovative concept for CO2 systems: the economizer.
This device was designed to significantly improve machine efficiency when outdoor temperatures rise. In such conditions, flash vapor production increases; by using a two-stage expansion scheme and having an auxiliary compressor for suction of the flash vapor from intermediate receiver, we managed to drastically increase cycle performance.
The first large-scale real-world application for a system with economizer followed in 2008, in Freiburg.
The control of new design proved to be quite difficult, due to huge variation of flash vapor mass flow.
2. Booster Systems and Double Stage: Efficiency in Retail
In 2007 two new companies entered the market of CO2 “transcritical systems”. One of them was based in Denmark - Advansor - and the other in Sweden - Green&Cool; I knew both founders very well as we had contact in the past years for the plants we built, with Costan, in Scandinavia.
Between 2007 and 2008, one of the most pressing challenges for supermarkets was reached: managing both “fresh” (medium temperature) and “frozen” (low temperature) products with a single centralized unit.
This led to the Booster system. Enex and Advansor developed circa at the same time the new circuit, a design with integrated MT and LT that was considerably more efficient than a cascade system. By eliminating the intermediate heat exchanger, the associated temperature difference and the resulting thermodynamic loss between LT and MT was removed.
Enex also refined the use of machines with two-stage compressors, produced at that time exclusively by Dorin—the only ones in the market who believed in this technology since the beginning.
3. The Market Challenge: Skepticism vs. Innovation
Despite the clear technical data, the initial market response was still characterized by strong skepticism. Many operators feared the high pressures and the apparent complexity of the new designs. The market was substantially limited to Switzerland, Scandinavia and UK.
There were, in that period, several attempts to design large heat pumps for sanitary hot water, similar to what was happening in Japan after the success of small “Ecocute”. All that was important also for refrigeration, as Swep developed - for the promising market of heat pumps - a high pressure water cooled gas cooler which could withstand 120 bar, the model B16DW, which could be used as heat recovery heat exchanger in refrigeration units for retail. Moreover, Dorin compressors were improved, thanks to an extended test campaign which lasted several months, in order to bring at highest level their reliability.
For Enex a commercial turning point came from Switzerland in 2007. Thanks to the foresight of partners like Frigo Consulting and Kaeltering, several cutting-edge systems were installed. The main markets for Advansor were initially Denmark and UK, and in particular one large retailer. In Scandinavia Green&Cool made quite well. There was a systematic lack of components, as valves, for example, but at this point it was possible to assemble refrigeration units which were reliable enough.
The request from the market was however very limited.