The graph in Figure 1 of the article "Air Conditioning for Humid Climates" (10/04) is misleading. The caption of the original figure, from a 1999 publication, indicated that it represented the annual sensible and latent loads for cooling ventilation air — that is, the annual load to cool one scfm of 100 percent outside air down to space conditions. The article implies that these are annual room cooling loads for one scfm of air. But 95 percent of residential systems process only return air, not 100 percent outdoor air. The outside air load comes from return duct leakage if the return leak is in the attic or crawlspace, or from infiltration. The statement that "on a hot, humid day in a house with a properly sized 5-ton cooling system, 3 tons of that capacity might be working to dehumidify the air, while 2 tons are working to actually cool it" is just plain wrong.
Donald P. Gatley, P.E.
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