- "Heat transfer has the greatest single effect on chiller performance. Large chillers can have more than five miles of condenser and evaporator tubes, so high heat transfer is fundamental to maintaining efficiency. Chiller efficiency declines rapidly when tubes become fouled. Contaminants, such as minerals, scale, mud, algae and other impurities, increase thermal resistance and reduce overall performance. These contaminants accumulate on the water side of heat transfer surfaces in both closed- and open-loop systems. Fouling occurs gradually over time, depending on the quality and temperature of the water used."
http://www.plantservices.com/articles/2004/192.html