The most commonly used refrigerant in RSW (refrigerated seawater) systems for fishing vessels today is HCFC-22 (R-22). However, the Montreal Protocol dictates the abolishment on the CFC and HCFC refrigerants, known to deplete the ozone layer if released t o the atmosphere. Other available alternatives are HFC refrigerants, which are strong global warming gases and highly taxed in Norway, or ammonia which needs special precautions due to its toxicity.
CO2 is an excellent alternative among the natural refri gerants, especially in applications where the toxicity and flammability of ammonia and hydrocarbons may be a problem. In preliminary calculations it has been shown that the energy efficiency is somewhat higher at low seawater temperatures, somewhat lower at high. Other investigations indicate higher efficiency figures for CO2 relative to halocarbon refrigerants.
A very interesting aspect of CO2 as refrigerant is the much smaller swept volume required, which mainly is a result of the higher operating pres sure for CO2. As illustrated in figure 1, the necessary swept volume of the compressor for CO2 is reduced to about 20 % of that required for HFC-404A. Therefore, the size of the compressors and tubing can be reduced significantly. This means that there ar e a potential to reduce the volume of the system, which is a very important indicator of cost of the system, but also an important indicator for a potential to reduce costs related to volume requirement onboard fishing vessels.
SINTEF Energy Research is very well prepared to develop a RSW CO2 system due to the already existing general knowledge base, available computer design-, simulation- and optimisation tools, well equipped laboratory facilities and skilled staff. This is a good basis for making a uni que and requested product. Hopefully it will also make the basis for other future products based on CO2 technology within the marine sector, both offshore and for the land-based fish processing industry.