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Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort. A duct system is also called ductwork. Planning (laying out), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design. [2]
Rooftop HVAC unit with view of fresh-air intake vent Ventilation duct with outlet diffuser vent. These are installed throughout a building to move air in or out of rooms. In the middle is a damper to open and close the vent to allow more or less air to enter the space. The control circuit in a household HVAC installation.
Industrial exhaust ducts are pipe systems that connect hoods to industrial chimneys through other components of exhaust systems like fans, collectors, etc. Ducts are low-pressure pneumatic conveyors to convey dust, particles, shavings, fumes, or chemical hazardous components from air in the vicinity to a shop floor or any other specific locations like tanks, sanding machines, or laboratory hoods.
In a UFAD design, conditioned air stays in the lower, occupied part of the room, while heat sources such as occupants and equipment generate thermal plumes, which carry the warm air and heat source generated pollutants towards the ceiling where they are exhausted through the return air ducts. [8]
There are two major systems to classify ductwork airtightness, one based on European standards, the other based on ASHRAE standard 90.1-2010.Both are based on the leakage airflow rate at a given ductwork pressure divided by the product of the ductwork surface area and the same ductwork pressure raised to the power 0.65.
A major consideration of duct design is to minimize duct pressure losses, turbulence, as poor duct geometry, increases turbulence, and increases plant electrical usage. Round duct work suction pressure collapse, in ducts over 6 feet in diameter, is prevented with rings at supports, and roughly 3 diameter centers.
Air streams are mixed to save energy and improve energy efficiency by partially recirculating conditioned air.. The most common application for an air-mixing plenum is the mixing of return air (or extract air) with fresh air to provide a supply air mixture for onward distribution to the building or area which the ventilation system is serving. [1]
HVAC turning vanes are sheet metal devices inside of mechanical ductwork used to smoothly direct air inside a duct where there is a change in direction, by reducing resistance and turbulence. See also