Basic Documentation

Table 1. Definition of Sizing Parameters.
Single-blade Damper Venturi Air Valve Sizing
Parameter
definition typical value definition typical value
Maximum
Airflow
A selected rating value. Above
this point, system may be
considered too loud or lose too
much pressure.
Often selected
between 2,000 and
3,000 fpm.
The flow rate approximately
maintained by the spring
when the actuator is at the
end of the stroke.
Typically occurs
at 1,700 to 1,900
fpm.
Minimum
Airflow
A selected rating value. Below
this point, the flow sensor may
be inaccurate. Depends on the
sensor and the required
accuracy.
Usually between 0
and 500 fpm.
The flow rate approximately
maintained by the spring
when the actuator is at the
other end of the stroke.
Typically occurs
at 100 to 200
fpm.
Maximum
Pressure
Drop
Above this pressure, control
may become difficult.
Dampers have been
applied successfully
at 6 in. WC of drop.
At this pressure drop, the
spring is fully compressed and
can no longer regulate airflow.
3 in. WC for all
available Venturi
air valves.
Minimum
Pressure
Drop
Pressure measured across the
fully open damper at a rated
flow.
Usually less than 0.1
in. WC.
At this pressure drop, the
spring is fully extended and
can no longer regulate airflow.
Usually 0.6 in.
WC or 0.3 in. WC
for low pressure
valves.
FLOW RANGES OF TERMINAL UNITS & VENTURI AIR VALVES
0 1000 2000 3000 4000 5000 6000 7000 8000
TYPE
LGS_04
AV_106
LGS_06
AV_108
LGS_08
AV_110
LGS_10
AV_112
LGS_12
LGS_14
AV_210
LGS_16
AV_212
AV_312
LGS_18
FLOW (CFM)
STARTING FROM
TU SHUT-OFF
AV CAL MIN
to FLOW SIGNAL
0.02" (~350FPM)
to 1000 FPM
Figure 5. Airflow Ranges for Venturi Air Valves
and Single-blade Dampers of Various Sizes.
Minimum Pressure Drop
Minimum pressure drop is an important parameter of
an airflow control device. It is the pressure drop
across a fully open device at a given airflow rate.
The minimum pressure drop (along with the
pressure drop of the other system components)
determines the static pressure that the supply and
exhaust fans must provide to achieve the desired
system airflow.
The system pressure drop is an important factor in
fan energy consumption. Designers motivated by the
Green Building movement and sustainability strive to
select low-pressure components, so they favor
single-blade dampers.
2 3
Like the air capacity, the minimum pressure drop
depends on the size of the airflow area. Figure 6
comp
ares of the airflow open area for a Venturi air
valve and a single-blade damper.
2. U.S. Department of Energy, Low-Pressure-Drop HVAC
Design for Laboratories, DOE/GO-102005-2042 (February
2005).
3. Siemens Building Technologies, Inc., Green Lab Facilities:
Steps Toward Sustainability Technology Report, 149-488,
(April 2008).
Siemens Industry, Inc. Page 5 of 8
Document No. 1
49-985