A: The cooling tower effectiveness equation isn't directly in the handbook — it's adapted from the direct evaporative cooler efficiency equation by substituting water temperatures for air temperatures, which is physically appropriate since water is the working fluid being tracked in a cooling tower. Sometimes on the PE exam you need to recognize that a formula's structure can be adapted to a slightly different scenario rather than looking for a formula that maps exactly to your problem. Understanding where the equation comes from conceptually lets you derive it or adapt it on the fly.