A new centralised cooling plant will annually save 800,000 kWh energy and secure optimal operation at Denmark’s second biggest hospital, Aarhus University Hospital.

Stability and efficiency are key words at the new centralised cooling plant at Aarhus University Hospital. This, the main hospital of Denmark’s second largest city Aarhus, has replaced a huge amount of old decentralised cooling units with one, new centralised plant with a cooling capacity of 2.5 MW. It improves the level of stability of the necessary cooling of surgery rooms, scanners, server rooms and IT-equipment. At the same time it facilitates the possibility of the operations department to control and run the complete cooling plant more effectively - with much lower energy consumption than before.

It is estimated that the hospital will save around 3.5 mio kWh of energy annually, due to the installation of a highly energy efficient heating and cooling system. The new system combines the cooling system with the heating system, an obvious solution, which is not used very much worldwide.

Environmentally friendly solution
The new cooling plant is not only more efficient but also more environmentally friendly than the old system:

“Many old units used the greenhouse gas Freon 22 as refrigerant - this is forbidden in all new cooling systems in Denmark, and at Aarhus University Hospital it has been replaced by natural refrigiants. The choice fell on chillers using R290 (propane, GWP*=3.3) and heat pumps using R600a (iso-buthane, GWP=4). Other options like CO2 had also been evaluated but were found to be less efficient in the applications and the temperatures required. This way about 750 tons of CO2 emissions are saved annually”, says engineer Lars Torp Larsen from ALECTIA, who has installed the new heat pumps as part of the consulting group DNU I/S.

Moreover, the new cooling system saves around 800,000 kWh of energy per year and surplus heat from the cooling plant is reused. All the environmentally friendly results are additional benefits of the installation of a much better cooling system, where state-of-the-art energy technology is being used to the benefit of the hospital patients and its staff.

High efficiency heat pumps and chillers
The new cooling plant consists of two large air/liquid heat pumps, 9 air-cooled chillers and a number of compressors. The units are called SAB LightTM from Johnson Controls. Danfoss VLT® drives control the speed of the units. The new technology used combined with the frequency converters contribute to the total energy savings.

During the months of June, July and August the heat pumps are able to deliver all the heat required at the hospital. Therefore no extra heat has to be delivered from the public districtheating network. Surplus heat from the cooling production during the summer is reused for heating purposes. During the winter the heat pumps deliver a smaller portion of the heat consumption, while the main heat supply is taken care of by the district-heating supplier, AffaldVarme Aarhus.