Problem 12.1: Why do large cooling systems move cooling with

From Chapter 12 Problem Set. Level 1: Conceptual Mastery.

Question

Why do large cooling systems move cooling with water rather than air? In your answer, reference specific heat, density, and the practical size of the distribution system.

Answer

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Air has a specific heat of approximately 0.24 BTU/lb·°F versus water’s 1.0, and is roughly 800 times less dense. To move the same BTU load, air-based systems require vastly greater volumetric flow through massive ductwork with high-powered fans. A chilled water system consolidates cooling into a central plant with compact piping – a six-inch chilled water pipe carries the same capacity as a four-foot air duct – with a fraction of the pumping energy and far simpler redundancy.