Sensible Heat Ratio (SHR)

Every cooling coil does two jobs at once, dropping temperature and wringing out water, and SHR says how the work splits. A dry Denver office runs SHR 0.90; a Houston restaurant with a hundred breathing customers and a dish line might sit at 0.65; a natatorium is lower still. Equipment has its own SHR, set by coil rows, fin spacing and face velocity, and the design rule is simple: the coil's SHR must be at or below the room's, or moisture accumulates.

This is where oversizing does its damage. A unit with more capacity than the room needs satisfies the thermostat quickly, runs short cycles, and never lets condensate form, so it delivers a high effective SHR regardless of nameplate, and the building runs 74 °F at 65 % RH with mould in the closets. Slowing the fan lowers coil SHR (colder, wetter coil); speeding it raises SHR. Worked example: 24,000 BTU/hr sensible plus 6,000 latent gives SHR = 24,000/30,000 = 0.80, the textbook residential default. Given SHR and one component you can recover the other: 30 kW sensible at SHR 0.75 implies 10 kW of latent load and a 40 kW coil.