ASHRAE Terminology

the static pressure existing at the outlet of an operating pressure relief device due to pressure in the discharge line.

in-line duct fan with centrifugal blades which can develop static pressures higher than normal duct fans. Also identified as a tubular centrifugal fan.

in a fluid-carrying pipe, a device with a reduced diameter to increase the fluid velocity sufficiently to induce a lower static pressure at that point to draw another fluid into the line.

device to maintain constant downstream static pressure or volume flow.

see static pressure loss.

see static pressure loss.

the fan total efficiency multiplied by the ratio of fan static pressure to fan total pressure.

the difference between the fan total pressure and the fan velocity pressure. Therefore, it is the difference between static pressure at the fan outlet and total pressure at the fan inlet.

the point of operation where the external static pressure is zero.

(1) normal force per unit area that would be exerted by a moving fluid on an infinitesimally small body immersed in it if the body were carried along with the fluid. (2) pressure exerted by a fluid at rest.

see static pressure loss.

(1) volumetric flow rate required to maintain a constant static pressure in the test section. (2) the amount of air interchanged between the room side and outdoor side through a unit as a result of construction features, faulty sealing techniques, temperature differential, or height differential. See infiltration.

small bore tube inserted perpendicular to a flowing stream with its orifice facing the stream to measure total pressure. At present, the term is often used for a double-tube instrument from which the flow velocity can be calculated with one orifice facing the flowing stream to register total pressure and the other perpendicular to the stream to register static pressure.

the static pressure of a fluid at the outlet of the pumping device, expressed in terms of the height of a column of the fluid or of the height of some manometric fluid that it would support.

static pressure relative to the atmosphere.

the actual pressure of the fluid, which is associated not with its motion but with its state. The pressure is exerted uniformly throughout the entire fluid. The portion of the fluid pressure which exists by virtue of the degree of compression only. If expressed as gage pressure, it may be negative or positive. In a dynamic system, static pressure is the difference between total and velocity pressures. in. H2O (kPa).

(1) external static pressure loss for forced-air systems using packaged air-handling equipment, the static pressure loss resulting from airflow through the supply and return ductwork and other elements external to the packaged air-handling unit. Compare to internal static pressure loss and total static pressure loss. (2) internal static pressure loss for forced-air systems, the static pressure loss resulting from airflow through the internal elements of the packaged air-handling unit. These internal elements may include such items as filters, coils, dampers, mixing sections, etc. Compare to internal static pressure loss and total static pressure loss. (3) total static pressure loss for forced-air systems, the sum of the external static pressure loss and the internal static pressure loss. See internal static pressure loss and external static pressure loss. The term is not applicable to an individual fan or a fan located within a builtup air-handling unit. Fans are rated by the term fan total static pressure, which is not the same as fan total pressure. Compare to fan total pressure.

method in which ducts are sized so that the regain in static pressure due to decreased velocity between two points totally or partially compensates for the frictional resistance between the points.

the static pressure of a fluid at the inlet of the pumping device, expressed in terms of the height of a column of the fluid or of the height of some manometric fluid that it would support. It is a positive value. See static suction lift.

the static pressure of a fluid at the inlet of the pumping device, expressed in terms of the height of a column of the fluid or of the height of some manometric fluid that it would support. It is a negative value. (See static suction head).

the pressure which exists by virtue of the degree of compression and the rate of motion. It is the algebraic sum of the velocity pressure and the static pressure at a point. Thus, if the fluid is at rest, the total pressure will equal the static pressure.

see static pressure loss.

in a turbocompressor, the ratio of the variation of enthalpy of an isentropically compressed vapor to the work to be effectively supplied to the compressor (the enthalpy relating to the total pressure of the fluid at inlet and the static pressure at outlet).

(1) in a moving fluid, the pressure that would induce an equivalent velocity if applied to move the same fluid through an orifice, so that all pressure energy is converted into kinetic energy. Velocity pressure is always a positive value, in. H2O (kPa). (2) the difference between the total pressure and static pressure (relative to the same datum).

contraction in a pipeline or duct that increases the fluid velocity to lower its static pressure, followed by a gradual expansion to allow recovery of static pressure. Used for metering and other purposes that involve change in pressure.