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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.
Cross-breezes work when two windows are opposite of each other. Cross ventilation is a natural phenomenon where wind enters an opening, such as a window, flows directly through the space, and exits through an opening on the opposite side of the building (where the air pressure is lower).
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]).
Air changes per hour, abbreviated ACPH or ACH, or air change rate is the number of times that the total air volume in a room or space is completely removed and replaced in an hour. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each hour.
Figure 1: Components of a centrifugal fan An external motor belt driven inline centrifugal fan discharging inline to the exterior of a building through a duct. Unlike non-inline/non-concentric impeller casing design with a cutoff blade above, the concentrically symetric cylinder casing and impeller geometry of inline type redirects the outflow around so that it is parallel to the inflow of gases.
In a water boiler, draft is the difference between atmospheric pressure and the pressure existing in the furnace or flue gas passage. [1] Draft can also be referred to as the difference in pressure in the combustion chamber area which results in the motion of the flue gases and the air flow.
Power flue – Fanned flues use the pressure created by a fan to power the movement of outside air into the appliance and combustion products to external air. Thus air and flue ducts can be much longer, of smaller diameter, and include changes of direction. Most ducting is concentric; the air duct contains the smaller flue duct within it.
The air column from a 3-foot-diameter (0.91 m) fan, therefore, has more than six times as much friction interface per volume of air moved as does the air column from a 20-foot-diameter (6.1 m) fan. [8] When the down column of air from an HVLS fan reaches the floor, the air turns in the horizontal direction away from the column in all directions.