New aalborg university hospital Ammonia district cooling
New Aalborg University Hospital under construction. Image from

Danish ‘Super’ Hospital Chooses Ammonia-Based District Cooling/Heating System

The ammonia system from Johnson Controls uses lake water as its cold source and will be up to eight times as efficient as conventional cooling systems, according to the utility provider.

A new 330,000m2 (3,552,090ft2) “super” hospital being built in Aalborg, Denmark, has chosen an ammonia/NH3 (R717)-based district cooling and heating system manufactured by Johnson Controls (JCI) and installed by utility provider Aalborg Forsyning, owned by the Aalborg municipality.

The New Aalborg University Hospital includes oncology wards, a psychiatric department, Aalborg University’s Faculty of Health Sciences, a patient hotel and more. It is expected to open in the first half of 2024.

The 11MW (3,128TR) ammonia system includes three Sabroe ChillPac ammonia chillers, two Sabroe HeatPac ammonia heat pumps, a heat exchanger and other auxiliary equipment. The system delivers 12°C (54°F) water to the hospital and the return temperature is 18°C (64°F).

The flexible combination of ChillPac and HeatPac units is also marketed by JCI as the Sabroe DualPac. 

“The project is expected to be one of the most energy-efficient refrigeration plants in the world, with an all-year efficiency of up to 23, where conventional plants are two to five,” said Michael Sandager, Project Engineer with Aalborg Forsyning. “So we expect to have a reliable system that is up to eight times as efficient as conventional cooling.”

This means that the hospital expects to save 80% of its electricity consumption, compared to the system in the old hospital, and 500–700 metric tons of CO2 per year. An additional benefit is that the facility “occupies much less space and eliminates noise and vibration,” JCI said.

Catering to patients

The ammonia district cooling/heating system will provide around 80% of the hospital’s cooling needs, including medical equipment cooling, air conditioning, cooling of servers and more. An important point in the system design is that the hospital patients need air that is carefully filtered and conditioned to provide comfortable temperature and humidity, particularly in the summer. This means that reliability is crucial, said Sandager, stressing that it was important to Aalborg Forsyning that the technology they chose was not experimental, but proven in the market already.

The system uses water from a lake as its cold source. The lake is artificial, created by the chalk mining activities of Danish cement manufacturer Aalborg Portland, and the water has a temperature between 5 and 13°C (41 and 55.4°F). 

In the colder months of the year, from December to June, the “free cooling” from the lake will be sufficient to cover all the hospital’s cooling needs, according to JCI. The rest of the year, the hospital will need additional cooling to meet peak demand.

“It would have been possible to simply install a chiller to cover the peak demand during the afore-mentioned [warmer] months, but Aalborg Forsyning opted to install a combined chiller and heat pump solution for greater flexibility,” JCI wrote in a case study. “This means they have the freedom to use a lower percentage of the available free cooling capacity and make the chiller do more work – i.e. working longer and harder to provide the required cooling.” “Meanwhile the diverted cold water can be used to drive the heat pump to produce hot water for other customers,” JCI added.

Want to find out more, or have something to say about this story? Join the ATMO Connect network to meet and engage with like-minded stakeholders in the clean cooling and natural refrigerant arena.

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