Bitzer’s fresh approach to cascades

GERMANY: The gourmet German food specialist Frische Paradies is using a state-of-the-art R134a/CO2 cascade system in its new supermarket in Stuttgart.

Opened in early July, the €10.5m supermarket has been designed in the style of a modern market hall and relies on Bitzer reciprocating compressors along with the German manufacturer’s attendant Varipack frequency inverters.

Every year, Frische Paradies supermarkets are required to refrigerate more than 21,000 tonnes of food and display more than 12,000 high-quality delicacies. Quality and freshness are its highest priorities.

Frische Paradies consulted with Michael Müller from Hamburg-based engineers Eneratio and decided on the R134a/CO2 solution to provide the best combination of energy efficiency, cost-effectiveness and operating reliability.

The R134a/CO2 cascade system was manufactured by Compact Kältetechnik GmbH and installed by Kratschmayer GmbH

Commenting on the selection of both the reciprocating compressors and frequency inverters from a single source, Kratschmayer’s Uwe Schmid-Böcker said: “This is a crucial advantage for a system where reliability comes first. We can be sure that the quality is high and that both components are optimally compatible with one another.”

The Varipack frequency inverters were connected to the control units planned and built by Kratschmayer in close coordination with Bitzer and data management equipment supplier Wurm.

Bitzer attended site for the initiation of the system in order to advise and assist the customer.

“Naturally we do not leave customers in the dark with our compressors and frequency inverters, even if there are specialists as experienced as Kratschmayer on hand,” commented Benjamin Vornweg, a technical consultant at Bitzer. “For instance, we assisted in the configuration of the Varipack frequency inverters in Frische Paradies so that we would be able to look over the customer’s shoulder and see how easy it was to configure and commission our product solution. Ultimately it gives the customer extra peace of mind to know that the system has been connected properly and the goods are absolutely safe.”

Separate frequency inverters are installed on the R134a and CO2 stages. The frequency range of the Varipack in Frische Paradies is 25 to 70Hz for the six-cylinder compressor for medium-temperature applications (R134a stage) and 30 to 65Hz for the two-cylinder compressor for low-temperature applications (CO2 stage). The speed of 65Hz meets the requirements of the customer. Generally speaking, CO2 compressors from Bitzer can be run at up to 70Hz for subcritical applications.

Five Bitzer Ecoline reciprocating compressors work in the R134a stage (one 6GE-30Y and four 4FE-25Y models). The 6GE-30Y is operated by an FHU+73 Varipack frequency inverter. This allows the compressor’s output to be adjusted to meet the actual demand, which results in excellent system efficiency and control quality. The R134a manages the temperatures of the medium-temperature consumers and dissipates the waste heat of the CO2 stage.

Four Bitzer Octagon reciprocating compressors (2ESL-4K) are used in the CO2 stage. In this stage, too, one of the compressors is operated by an FEU+16 Varipack frequency inverter.

An advantage of the Varipack frequency inverter is that it can be operated in two ways. They are either dependent on an external set point signal – as in the case of Frische Paradies – or they can regulate smaller systems with up to two compressors with an optionally available extension module. In this case, the Varipack frequency inverters regulate the evaporation and condensing temperatures and can switch on a second fixed-frequency compressor. They can also be fully integrated into the switchboard or mounted via push-through installation. In the push-through installation variant, the rear part of the frequency inverter that is to be cooled is ‘pushed’ through the switchboard wall in order that the waste heat does not affect the interior of the switchboard. ‘A good and interesting solution proposed by Bitzer,’ says Uwe Schmid-Böcker.

The Varipack said to be extremely easy to commission thanks to its preconfigured BEST (Bitzer Electronic Service Tool) software.

Besides managing the frequency inverters, the master control system from Wurm carries out all regulatory, control and monitoring tasks. Of particular note is the special heat recovery module which was designed to manage a heat recovery circuit by feeding waste heat from the R134a stage into a 15,000-litre water tank.

A specially programmed main module from Wurm also manages peripheral system components such as pumps, ventilators and a glycol circuit. All control circuits can be operated and integrated into remote data monitoring with the Frigodata software.