Which statement best describes the effect of fouling on a cooling tower?

• A. Fouling improves heat transfer efficiency.
• B. Fouling has no effect on performance.
• C. Fouling reduces energy consumption.
• D. Fouling reduces heat transfer efficiency and increases energy consumption.

Answer: (D)

Fouling adds deposits to the cooling-tower surfaces, creating an insulating layer that increases thermal resistance. This lowers the heat transfer coefficient, so the tower can reject less heat for the same water and air flow. To achieve the same cooling load, the system must move more water or air and run pumps and fans longer or harder, which drives up energy use. So the statement that fouling reduces heat transfer efficiency and increases energy consumption is the best description. The other options are inconsistent with how fouling impacts performance: it does not improve transfer, it does affect performance, and it typically increases—not decreases—energy use.