The Six Senses hotel opened in Crans-Montana, Switzerland, in February 2023. (Source: Six Senses)
The Six Senses hotel opened in Crans-Montana, Switzerland, in February 2023. (Source: Six Senses)

Luxury Swiss Hotel Installs Transcritical CO2 Booster System for Refrigeration and Heat Recovery

Ultrafroid, a Swiss refrigeration contractor, has installed a transcritical CO2 (R744) booster system – manufactured by Italian OEM Enex – in a new Six Senses hotel at the Crans-Montana ski resort in Switzerland.

The refrigeration system, which was commissioned in early December 2022, serves 26 medium-temperature (MT) cold rooms, 11 refrigerated Ginox cabinets and 5 low-temperature (LT) cold rooms across the hotel’s seven restaurants and bars. It also provides space heating and hot water for the hotel via heat recovery, explained Cédric Zufferey, Technical Officer at Ultrafroid.

While the seven-story luxury hotel opened on February 1, 2023, installation for the refrigeration system’s piping began in mid-2021, he added.

Reliable and efficient

The CO2 rack consists of six semi-hermetic reciprocating compressors from Italian manufacturer Dorin. Four of the compressors serve MT and the remaining two are for LT, said Zufferey.

“We only use Dorin compressors for COsystems since we started installing them,” he said. “They are very reliable and efficient.”

Ultrafroid’s transcritical CO2 rack at the Six Senses hotel in Crans-Montana, Switzerland. (Source: Ultrafroid)
Ultrafroid’s transcritical CO2 rack at the Six Senses hotel in Crans-Montana, Switzerland. (Source: Ultrafroid)

The system offers a capacity of 52kW (14.8TR) for MT, with supply temperatures of 1 to 10°C (33.8 to 50°F) and 8kW (2.3TR) for LT at -21°C (-5.8°F).

Due to the small capacity of the system and the ambient temperatures at the resort – which do not tend to exceed 29°C (84.2°F) – the system does not need any ejector or parallel compression technologies, he explained.

“The system is very efficient compared to alternatives,” he added.

To further improve the efficiency of the system, 100% of its waste heat is recovered for space heating and hot water via an Alfa Laval brazed plate heat exchanger. A second, emergency heat exchanger from Italian manufacturer Klimal is used as a backup to disperse excess heat if heating demand is not high enough to require all of the system’s heat.

Fewer refrigerant leaks

The system at Six Senses is monitored by a total of 51 controls from Swiss manufacturer Digitel, explained the company’s CEO, Marc-Etienne Jan.

The whole system is monitored via Digitel’s central DC58-2 unit, which is installed next to the rack and connects to the rest of the controls in the rack and around the hotel.

Four DC24TR controls monitor the high and medium pressures of the booster system and heat recovery.

The six compressors are managed via three DC24D and three DC25 controls. According to Digitel, Enex built these controls into the rack’s electrical panel during manufacturing for smoother integration.

Thirty-one DIN-mounted DC24DE controls are installed in the hotel’s cold rooms, and 12 compact, panel-mounted DC24EE controls are installed in the system’s refrigerated cabinets. These units control super heat by means of an electronic expansion valve, said Jan.

The Six Sense hotel in Crans-Montana has a total of 31 cold rooms – 26 medium-temperature and 5 low-temperature. (Source: Ultrafroid)
The Six Sense hotel in Crans-Montana has a total of 31 cold rooms – 26 medium-temperature and 5 low-temperature. (Source: Ultrafroid)

Ultrafroid, which monitors the system, can remotely access the system’s performance data via Digitel’s TelesWin software. It also allows Ultrafroid to change system parameters and check maintenance requirements.

To ensure the health and safety of hotel staff and guests, around 96 leak detectors were installed around the system. However, Zufferey noted that due to the high-pressure welding requirements of the system’s stainless-steel piping, leaks are very rare, which makes transcritical COinstallations much more reliable.

“It’s incredible; we have a lot [fewer] problems with CO2 installations than the old ones with synthetics,” he said.

“It’s incredible; we have a lot [fewer] problems with CO2 installations than the old ones with synthetics.”

Cédric Zufferey, Ultrafroid

Growth of CO2 in Switzerland

Ultrafroid installed its first CO2 system in Switzerland in 2003 in partnership with Enex, said Zufferey. Since then, the company has installed 60 CO2 systems, with the majority being in supermarkets.

While the type of system installed at the Six Senses in Crans-Montana is not commonly used in hotels or restaurants, laws in Switzerland left very few options for this project, he explained.

“In Switzerland there aren’t many choices for this kind of installation; because of the law we only have two choices,” he said. “We could use a chiller with a secondary circuit with glycol, for example, on a subcritical CO2 installation, or a complete CO2 installation like this one.”

Due to the amount of piping used in the installation – and therefore the required refrigerant charge – and the capacity of the system, synthetic refrigerants were not an option. Because of these regulations, the majority of new commercial installations and 100% of new supermarket installations in Switzerland are now CO2, he added.

Ultrafroid has been working with Digitel for around 10 years, with the two companies collaborating on more than 20 CO2 installations in total. Outside of its partnership with Ultrafroid, Digitel has been involved in 30 other CO2 installations across Switzerland, France and Germany, most of which are supermarkets, said Jan.

“Switzerland is very advanced in terms of CO2 installations because they started earlier, but others are catching up,” he said, noting that installations in France and Germany tend to be much larger than their Swiss counterparts.

“Switzerland is very advanced in terms of CO2 installations because they started earlier, but others are catching up.”

Marc-Etienne Jan, Digitel

Jan and Zufferey attributed part of CO2’s successes in Switzerland to the Kältering Group, which is a Swiss association of many refrigeration companies that has helped with R&D, education and training.

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