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Displacement ventilation systems supply air directly to the occupied zone.The air is supplied at low velocities to cause minimal induction and mixing. This system is used for ventilation and cooling of large high spaces, such as auditorium and atria, where energy may be saved if only the occupied zone is treated rather than trying to control the conditions in the entire space.
Cement and lime plant duct velocity at normal operations is 3000 to 3200 foot per minute, lead plant velocities are 4000 to 4500 foot per minute, as the dust is heavier. Other industries, such as grain have lower gas velocities. Higher duct gas velocity may require more powerful fans than lower duct velocities.
Displacement ventilation is best suited for taller spaces (higher than 3 meters [10 feet]). [2] Standard mixing ventilation may be better suited for smaller spaces where air quality is not as great a concern, such as single-occupant offices, and where the room height is not tall (e.g., lower than 2.3 meters [7.5 feet]).
The UFAD system was originally introduced in the 1950s for rooms with high heat loads and raised floors systems for cable and equipment management (e.g. computer rooms, control centers, etc.). The system was introduced into office buildings in the 1970s in West Germany, with the addition of occupant-controlled localized supply diffusers.
A diffuser is "a device for reducing the velocity and increasing the static pressure of a fluid passing through a system”. [1] The fluid's static pressure rise as it passes through a duct is commonly referred to as pressure recovery. In contrast, a nozzle is used to increase the discharge velocity and lower the pressure of a fluid passing ...
The viscous friction causes the flow properties to change along the duct. The frictional effect is modeled as a shear stress at the wall acting on the fluid with uniform properties over any cross section of the duct. For a flow with an upstream Mach number greater than 1.0 in a sufficiently long duct, deceleration occurs and the flow can become ...
A duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the fan flow.
Ducts for air pollution control in a 17000 standard cubic feet per minute regenerative thermal oxidizer (RTO). A round galvanized steel duct connecting to a typical diffuser Fire-resistance rated mechanical shaft with HVAC sheet metal ducting and copper piping, as well as "HOW" (Head-Of-Wall) joint between top of concrete block wall and underside of concrete slab, firestopped with ceramic ...