We study fan performance by using scaling law among the variables such as fan static pressure
head, volume flow rate, air density, rotational speed, fan diameter, and input power.
Fan static pressure
rise was measured with a hand-held micro-manometer.
For the fan energy differential to dominate the latent energy differential, the system fan static pressure
would have to be high; or the system would have to operate at near-peak airflow a large number of hours; or the system would have to be located in a very dry climate where the ambient summer absolute humidity is below about 55 grains (121.3 g/kg) [humidity ratio 0.0079], which is not the case in any of the 'A' climate zones5 (2A, 3A, 4A, 5A, etc.) in the eastern two-thirds of the United States.
IV=internal variables generated from fan laws (B1 and B2) using the input fan static pressure
([P.sub.B0]) where ([P.sub.B0]=[P.sub.B1]=[P.sub.B2]) see Figure 1:
Though fan total pressure does diverge from fan static pressure
as flow increases as shown in Figure 2, the magnitudes of the two measurements for this series FPTU are of the same magnitude over the range of values tested.
Quantity Symbols n impeller rotational speed [p.sup.fs] fan static pressure
[P.sub.r] fan shaft input power [p.sub.t] total pressure [q.sub.v] volumetric airflow rate [[eta].sub.ed] overall fan efficiency when the fan total pressure is included through a test with outlet duct [[eta].sub.esd] overall fan efficiency when tested without outlet duct BY ARMIN HAUER, MEMBER ASHRAE
Finally, the fan static pressure
, [P.sub.sf], is the fan total pressure less the fan velocity pressure ([P.sub.sf] = [P.sub.tf] - [P.sub.vf]).
In either case the energy input will always closely approximate that occurring when the filters are dirty and upon which the fan static pressure
wg (Pa) [Power.sub.fan] = power consumption of terminal unit fan/motor, W [P.sub.s] = fan static pressure
Consider each of the quantities, specifically total fan pressure, fan velocity (dynamic) pressure, and fan static pressure
, described in detail below.
The fan static pressure
requirement for the heavy and extra heavy hoods is more than 2.0 in.
(c.) Fan energy calculation assumes the following fan static pressures
: --Single wheel AHU (Scenarios A and C): Supply fan static pressure
of 3.5 in.