Briefs: A CO2 secondary refrigerant system to test icebreakers

Travelling through the North Pole's ice-capped seas could reduce sea transport distances between Hamburg and Osaka, Japan, or Shanghai, China, for instance, by more than 4000 nautical miles, thus allowing for great time and financial savings. The Ice Breaking Laboratory, situated in Helsinki, designs icebreakers and vessels that can sail through ice capped seas, for Aker Arctic Technology Inc. All new ships are tested as models in the laboratory's ice model tank, which includes an 8 x 60 m surface with up to 100 mm thick ice. Previously ice thickness was only 26 mm, but thanks to the equipment newly designed by York/Johnson Controls, Finland, this has improved. CO2 was chosen as a heat transfer medium from 4 screw compressors (vs. ammonia which could not be used here) with R-404A as refrigerant. The system uses 100 kg of R-404A and 2 tonnes of CO2 and has a capacity of 200-500 kW, delivering air temperatures down to between -6°C and -27°C. The ice is made by spraying fresh water over the pool through 118 gravity coils, divided into 6 separately controllable groups, placed over the pool and ensuring that the ice is as even as possible. During freezing, a heat recovery system saves hot water in a 50 m3 (2500 kWh) tank which is used to melt the ice once it has been broken.