CO2 system for the Copenhagen metro | HiRef S.p.A.


CO2 system for the Copenhagen metro

CO2 system for the Copenhagen metro

  • Buildings

Year: 2019

Location: Copenhagen, Denmark

Product category: Heat pumps

The Copenhagen underground to choose CO2 technology by HiRef. A transcritical system that uses the natural refrigerant CO2 R744.

Environmental and social sustainability as a top priority

customer's request

Environmental and social sustainability as a top priority

Denmark is first and foremost an environment-friendly country, and for the air conditioning of the new underground server room of the Copenhagen metro, it chose a system made by HiRef and using a natural refrigerant.

The most popular option offered by the other bidding contractors was propane (R290): natural, and with a very low environmental impact. The limit of this hydrocarbon, however, is flammability, a feature that can turn a highly environment-friendly substance into a deadly hazard for human health.

The choice of CO2


The choice of CO2

HiRef proposal was judged the best combination of reduced environmental impact and protection of human health - based as it is on a transcritical regime that uses the natural refrigerant CO2 (R744).

CO2 is natural, has a global warming potential (GWP) equal to 1 and is not flammable, however, it is more challenging to manage than other refrigerants and requires a specific conditioning system with higher production costs. These aspects did not deter the client who chose CO2 as a refrigerant, a friendly option for the environment with a strong focus on human health. A highly valuable choice!


The system consists of 4 air-cooled water chillers of the CDA series.

The units are built with independent refrigeration circuits with modulating compressors to boost the system energy efficiency, also obtained thanks to the innovative gas cooler pressure optimisation system, able to maximise output in all operating conditions (patent registered by HiRef S.p.A.).

The new chillers replaced obsolete machinery, in installation settings characterised by major architectural constraints.

This achievement was the result of the collaboration between HiRef's R&D department and HiRef's subsidiary Tecno Refrigeration, the Group company with the highest level of CO2 expertise.

In addition to consultancy on system construction, a FAT test was also carried out in HiRef's Tribano facility near Padua, in the presence of the customer and delivering specific technical training to the personnel in charge of installation locally.

Units installed:

1x CDA91FL


Plant power rating: 500 kW


The unit functions and efficiency were tested to verify operation according to design.

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