The resistance of duct fittings must be determined carefully so air flow at outlets will be the same as called for in the building design. The DFDB [ASHRAE, 1994] lists the dynamic loss coefficient, C, for 228 duct fittings. When more than one type of fitting can be used equally, the fitting with the smaller loss coefficient should be chosen. However, a higher-pressure-loss fitting may be desirable if the fitting is located in a branch near a fan or helps provide pressure balancing. Specific examples of fitting performance based on energy consumption are provided elsewhere in this chapter.
