U-38
CHAPTER 4
•
Characteristics
1. How to Read the Characteristic Curves
1.1 Obtaining Characteristics from Static Pressure Loss
(1) Static pressure loss from a straight pipe duct length (at required air volume)
(2) Static pressure loss at a curved section (at required air volume)
(3) Static pressure loss of related parts (at required air volume)
Total static pressure loss
Estimated static pressure loss curve
obtained from
and
Air volume
Static
pressure
Intersection with air volume static
pressure characteristic curve
Air volume at application point
Total static
pressure loss
Static pressure loss at
application point
Required air
volume
2. Calculating Static Pressure Loss
2.1 How to Read the Air Volume - Static Pressure Curve
It is important to know the amount of static pressure loss applied
onto the Lossnay when using ducts for the air distribution. If the
static pressure increases, the air volume will decrease. The air
volume - static pressure curve (Q-H curve) example shows the
percentage at the decrease. A static pressure of 0.08 in H2O (19.6
Pa) is applied to Point A, and the air volume is 300 CFM (500 m
3
/
h). The duct resistivity curve shows how the static pressure is
applied when a duct is connected to the Lossnay. Thus, the L =
32.7 ft (9.97 m) duct resistivity curve in the diagram shows how the
static pressure is applied when a 32.8 ft (10 m) duct is connected.
Intersecting Point A on the Lossnay Q-H curve is the operation
point.
Duct Resistivity Curve
300CFM
(500 m
3
/h)
0.08 in H
2O
(19.6 Pa)
L = 32.8 ft (10 m)
A
64 ft (20 m)
48 ft (15 m)
33 ft (10 m)
16 ft (5 m)
Q-H curve
Static pressure
Duct resistivity curve
Air volume
Air volume
Static pressure
(Duct length)
Example
Duct Static Pressure
When duct is long Increases
If length is the same but the air volume Increases increases
If the duct diameter is narrow Increases
If the duct inner surface is rough
(such as a spiral)
Increases
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