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An ammonia refrigerated sea water system with a total refrigeration capacity of 480kW has been delivered to replace an out-dated freon system with a total capacity of about 350kW. The ammonia system allows for significantly faster cooling times, while it does not require more energy than the previous system even though the refrigeration capacity of the compressors has increased by 40%.

“With the new system there is no ice required and the chilling time is still less than what they achieved before with ice,” said Evert Potgieter of PAM Refrigeration, the company that completed the new installation on board the Ruwekus fishing vessel. The new system can chill the total catch of 200 ton sardine from +18°C down to -1°C in less than 5 hours. Measurements of the cooling time showed that the actual time to cool the same quantity of water compared to the old system was less than half the time.

Other system features include:

• A large titanium chiller and a condenser suitably sized for sea water condition over +25°C.
• Two new Grasso screw compressors, ‘model E’ each with 75kW electrical motors
• Titanium heat exchangers to avoid corrosion of and leakages from the tubes from the heat exchangers
• No ice is required with the new system unlike with the old one

Ammonia system ensures efficiency improvements

One of the technical challenges was to design the system in a way that the increased refrigeration capacity did not imply increased energy requirements and so that the refrigeration system could still be powered by the existing power generator on board the vessel.

Indeed, thanks to improved efficiency, the ammonia system does not require more energy than the previous system even though the refrigeration capacity of the compressors has increased by 40%. Moreover, a larger condenser reduces the absorbed power of the screw compressors, contributing to the improved energy requirements.