The Energy Penalty of Poor Duct Design
March 01, 2001
A home with a poor duct system can't be energy efficient no matter how tight or well-insulated it is.
My company, Energy Master Home Incorporated, recently renovated a duct system for an energy association officer who had tried to build a model energy-efficient home for himself and his family. He had taken pains to follow every recommendation of a well-known energy guru. His house was tight and well insulated-although not as well insulated as he thought-and there was little we could do to reduce his heating and cooling loads. But, his ducts were a different story. The ducts were delivering 1,493 CFM of conditioned air from a two-stage, 5-ton geothermal heat pump (when it was operating at high speed). Since 400 CFM are needed to effectively deliver each ton of cooling capacity, the ducts were essentially strangling the air conditioner. It was delivering only 80% of what it could produce. As it turned out, ACCA Manual J load for the house was 4 tons. As the ducts were delivering almost 4 tons of conditioned air, the customer and his family were not unduly uncomfortable. This situation presents an all-too-common dilemma for the whole-house auditor. Strangely, the inefficiency of the duct system was compensating for oversized equipment. ...
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