A municipal ice skating rink in Aarhus, Denmark, has realized energy consumption savings of 50% by installing a CO2 (R744) rack as well as a floor with CO2 pipes underneath rather than a water/glycol secondary system.

The direct expansion R744 system, a SteelX rack from Danish OEM Advansor that is equipped with heat recovery, was installed in 2019 by Danish contractor Multi Køl & Energi A/S. The project also included the installation of a new pump system to distribute the CO2 through the pipes, along with new insulation, lighting, ventilation and heating in the rink.

The project was part of Aarhus Municipality’s wider goal to reduce energy consumption across its building stock. The CO2 cooling system replaced an ammonia brine chiller that was no longer efficient enough.

The choice to install pipes to pump the CO2 refrigerant directly under the ice, rather than employ a secondary glycol loop, was made to achieve the most stable temperature across the entire rink, which results in the best possible ice quality. “The whole ice rink floor had to be dug up and replaced, so it was decided to pump the CO2 refrigerant directly into pipes under the rink floor,” said Anders Mønsted, Business Developer for the Industrial Segment at Advansor. “That solution is not possible with ammonia, and this is partly where the energy savings are achieved.”

“Our new CO2 refrigeration solution from Advansor has met our expectations in every way,” said Nicolaj Kiilerich, Project Manager at the Department of Technical Services and Environment, City of Aarhus. “We have reduced our electricity consumption for the refrigeration system by 50%, while the heat recovery system has also reduced our district heating consumption. All in all, we are very happy.”

The SteelX solution chosen by Aarhus includes parallel compression, permanent magnet motors and an HP gas ejector. The cooling capacity is 405kW (115TR) at -6°C (21.2°F) and 30°C (86°F) ambient temperature. The ice rink’s system was designed for a COP of 2.8, according to Mønsted.

The set point temperatures are -10°C (14°F) for ice hockey games, -8.6°C (16.5°F) for ice hockey training, -11°C (12.2°F) for figure skating and -12°C (10.4°F) for curling. When the rink is closed, the set point is -6.5°C (20.3°F).

“Our new CO2 refrigeration solution from Advansor has met our expectations in every way.”

Nicolaj Kiilerich, City of Aarhus

The original CO2 rack

The SteelX rack from Advansor is the original model in Advansor’s portfolio, and it is billed as a “robust, ultra-high quality” system that is fully customizable.

It has frequency inverters installed on the MT1 compressors, as well as low-temperature suction accumulators, liquid injection and a hot-gas dump as standard. Several types of controls are available, including from Danfoss, Carel and Würm.

Optional features on the SteelX include advanced heat recovery, permanent magnet motors, ejectors, a gas cooler bypass, a subcooler, and hot gas defrost.

The SteelX from Advansor is ISO 9001:2015 certified.

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