Evaluation of different evaporator and condenser concepts in sea water chillers using CO2 as refrigerant.

On board cooling of pelagic fish has often been performed using a Refrigerated Sea Water (RSW) refrigeration plant with halocarbon HCFC 22 as working fluid. According to EU-regulations, refilling of this fluid is not allowed from 2015. HFC alternatives may have considerable greenhouse warming potential and are heavily taxed in some countries, thus only a short time solution. The main natural alternative, ammonia, has significant drawbacks that can be unacceptable particularly for smaller vessels and for rebuilding of existing ships. Carbon Dioxide (CO2) is an environmental friendly, inexpensive, non-toxic, non-flammable alternative. One drawback is the high operating pressure which could give heavy, bulky and expensive heat exchangers. Different CO2-evaporator and condenser solutions were installed and tested on three fishing boats. One boat has pillow (dimple) plates and two boats have tube in shell type with either CO2 on shell side or CO2 inside tubes. This paper presents and compares the different heat exchanger solutions and boat owners experience using the CO2 RSW-system.