From Cold Air Distribution: System Design Guide

4.7 Duct Leakage

Leakage of supply air from ducts reduces the cooling capacity delivered to the conditioned space. If the leakage is to an unconditioned space, it represents an increase in the total load and a loss of energy from the system. If the leakage is to a conditioned space such as a return air plenum, the cooling capacity is not entirely lost from the system, but additional supply air must be provided to meet the space loads.

Leakage can also cause condensation on adjacent surfaces if the supply air temperature is lower than the ambient dew point. This concern is heightened with cold-air distribution systems.

The HVAC Air Duct Leakage Test Manual (SMACNA 1985) defines leakage classifications and provides a method for rating, analyzing, and testing duct leakage. The leakage class, C L, is a number proportional to the leakage in cfm/100 ft 2 (L/s per m 2) of duct surface at 1 in. w.g. (250 Pa) static pressure.

ASHRAE/IESNA 90.1-1989 (ASHRAE 1989) recommends that ductwork designed to operate at static pressures above 3 in. w.g. (746 Pa) be constructed and leak-tested to leakage class 6 or better. A leakage class of 3 is attainable for all duct systems by careful selection of joints and sealing methods and by good workmanship (SMACNA 1990; ASHRAE 1993).

Although leakage as a percentage of total flow rate is a useful criterion for system analysis, the SMACNA leakage classifications and test method require evaluation in terms of leakage...

Copyright American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 1996 under license agreement with Books24x7

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Air Handlers
Air handlers are a system-like device used in ventilating systems. They typically consist of a blower, heat exchange medium for heat or air conditioning, and housing.
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Variable air volume (VAV) units are manufactured assemblies of air valves and dampers contained in a single enclosure. As HVAC system components, they regulate airflow to a room or zone in response to a thermostat or other signaling device.
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HVAC ductwork includes pipe or closed conduits made of sheet metal, fiberglass board, or other suitable material for conducting air to and from an air handling unit.
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Air hose and air duct hose is used in pneumatic systems and controls, or as supply lines for pneumatic devices and tools.
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HVAC fans and blowers are used to move air through heating, ventilating, and air conditioning (HVAC) systems. They are an integral part of the air handling systems that bring or draw fresh air into buildings.

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