Daikin VAM-FA8VE Technical Data Manual page 259

• HRV • VKM-GA(M)V1
11.2.2 Air Flow (Quantity), and Dynamic and Static Pressure
Ventilation fan performance parameters include air flow (quantity) and static pressure. These two
parameters relate closely to each other. Ventilation cannot be designed without these two parameters. The
first step of "designing a ventilation system" is to understand these two parameters.
Quantity
Air flow is the amount of air that a ventilation fan exhausts (or supplies) per unit time, generally expressed
in m
Pressure
This is a wind pressure expressed in the unit of Pa. Three types of wind pressure are used.
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•
•
Relationship between pressure types
"Static pressure (Ps)" is a pressure needed for overcoming the resistance of the duct when conveying air.
"Dynamic pressure (Pv)", on the contrary, is a pressure due to air stream. To determine air velocity,
measure the dynamic pressure of the air.
The "total pressure (Pt)" is the sum of static pressure and dynamic pressure.
Pt = Ps + Pv = Ps +
P-Q Curve (static pressure - flow characteristic curve)
"P-Q Curve" shows the performance of a ventilation fan by indicating the relationship between air flow and
static pressure.
Fig. a shows a case with a wall-mount supply opening that is so small that the internal pressure becomes
slightly lower than the atmospheric pressure. The static pressure is B mm.
Fig. b shows a case with a wall-mount supply opening that is so large that the internal pressure becomes
almost equal to the atmospheric pressure. The static pressure is 0 Pa.
• HRV • Heat Reclaim Ventilation
3 3
/h or m /min.
Dynamic pressure
This is a pressure produced by wind velocity, also called "velocity pressure." Deflection of a window
glass by strong wind during typhoon is due to this dynamic pressure.
Static pressure
When a balloon has been inflated, there is a pressure in the balloon that presses against the
membrane of the balloon. Static pressure is produced also when the air is still.
Total pressure
This is the sum of wind's dynamic pressure and static pressure.
Fan
Water column
manometer
2
V
γ
2g
Fig. a
Small
supply
port
Static
pressure
Stream
Ps Pv
(Static pressure) (Dynamic pressure) (Total pressure)
V : velocity (m/sec)
g : Acceleration of gravity (m/sec
γ : Air density (kg/m
3 )
Fig. b
Slightly lower
than the
atmospheric
pressure
No difference
Static pressure = point B
Static
Air flow = point B'
pressure
3
Air flow (m /h)
Pt
2
)
Large
supply
Almost equal
port
to the
atmospheric
pressure
Static pressure = 0
Air flow = point C'
3
Air flow (m /h)
2
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