A Laboratory Study of Pressure Losses in Residential Air Distribution Systems

March 7, 2002 - 12:00pm
Bldg. 90
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An experimental study was conducted to evaluate the pressure drop of residential air distribution system components that are either not available or poorly described in existing duct design literature. The tests were designed to imitate cases normally found in typical residential and light commercial installations. The study included three different sizes of flexible ducts, under different compression configurations, splitter boxes, supply boots, and a fresh air intake hood. The experimental tests apparatus followed ASHRAE Standard 120P - Methods of Testing to Determine Flow Resistance of HVAC Air Ducts and Fittings. The flexible duct study covered compressibility and bending effects on the total pressure drop, and the results showed that the available published references tend to underestimate the effects of compression in flexible ducts. The supply boots were tested under different configurations including a setup where the flexible duct elbow connection was considered as an integral part of the supply boot. The supply boots results also showed that diffusers have a major effect on the pressure losses in exit fittings. The study consisted of two parts: Component Analysis, and Complete System Analysis. Our component analysis results gave a better estimation of the total pressure drop in the complete system, compared with coefficients from existing literature. Our results help as new data for residential duct design. The results showed that it is crucial for designers and contractors to be aware of the compressibility effects of the flexible duct, and the installation of supply boots and diffusers, as they can increase the pressure drop by factors of two to five for the boots and nine for the flexible duct.

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