Determining Damper Size - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

CHARACTERISTIC RATIOS =
100
20 10 5 3 2
0
0
% DAMPER OPENING
Fig. 29. Damper System Characteristics of
Parallel Blade Dampers.
CHARACTERISTIC RATIOS =
100
20 10
0
0
% DAMPER OPENING
Fig. 30. Damper System Characteristics of
Opposed Blade Dampers.
To achieve performance closest to the ideal linear flow
characteristic, a characteristic ratio of 2.5 for parallel blade
dampers (Fig. 29) and 10 for opposed blade dampers (Fig. 30)
should be used. The percent of the total resistance needed by
the damper can be determined by:
Total resistance (100%) = damper resistance + series
Characteristic ratio
(Fig. 29 and 30) = (Fig. 29 and 30)
Substituting (total resistance – damper resistance)
for series resistance:
ENGINEERING MANUAL OF AUTOMATIC CONTROL
SERIES RESISTANCE
DAMPER RESISTANCE
1
INHERENT
CHARACTERISTIC
100 C1498
SERIES RESISTANCE
DAMPER RESISTANCE
5 3 1
INHERENT
CHARACTERISTIC
100
C1499
resistance
series resistance
damper resistance
DAMPER SELECTION AND SIZING
total resistance – damper resistance
Characteristic ratio =
or
=
For parallel blade dampers:
2.5 =
Damper resistance = 29% of total resistance
or
29
= 41% of series resistance
100 – 29
For opposed blade dampers:
10 =
damper resistance
or damper resistance = 9% of total resistance
9
= 10% of series resistance
100 – 9
For example, if a coil (Fig. 31) with a pressure drop of 0.140 kPa
is located in series with an opposed blade damper, the damper
should have a pressure drop of 0.014 kPa (10 percent of 0.140
= 0.014).
0.014 kPa
DROP
Fig. 31. Typical Pressure Drop for Coil and
Damper (Series Resistance).

DETERMINING DAMPER SIZE

The desired relationship of damper resistance to series
resistance developed in DAMPER CHARACTERISTICS is
used to determine the desired damper pressure drop. This
pressure drop is then used in the damper sizing procedure in
Table 4.
For example, for a 915 mm by 1625 mm (1.487 m
with an airflow of 9.45 m
across a parallel blade damper, determined the damper size as
shown in Table 5.
459
damper resistance
total resistance
– 1
damper resistance
100
– 1
damper resistance
100
– 1
0.140 kPa
DROP
M15303
3
/s and a pressure drop of 0.014 kPa
2
) duct