Honeywell AUTOMATIC CONTROL User Manual

ENGINEERING MANUAL OF AUTOMATIC CONTROL
DAMPER SELECTION AND SIZING
465
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
resistance
Substituting (total resistance – damper resistance)
for series resistance:
Fig. 29. Damper System Characteristics of
Parallel Blade Dampers.
100
0
0
% DAMPER OPENING
% FULL AIRFLOW
C1498
100
CHARACTERISTIC RATIOS =
SERIES RESISTANCE
DAMPER RESISTANCE
INHERENT
CHARACTERISTIC
20 10 5 3 2 1
100
0
0
% DAMPER OPENING
% FULL AIRFLOW
C1499
100
CHARACTERISTIC RATIOS =
SERIES RESISTANCE
DAMPER RESISTANCE
INHERENT
CHARACTERISTIC
5 3 120 10
or
For parallel blade dampers:
Damper resistance = 29% of total resistance
or
For opposed blade dampers:
or damper resistance = 9% of total resistance
For example, if a coil (Fig. 31) with a pressure drop of 0.55
(in. wc) is located in series with an opposed blade damper, the
damper should have a pressure drop of 0.06 (10 percent of
0.55 = 0.06).
Characteristic ratio
(Fig. 29 and 30) =
series resistance
damper resistance
2.5 =
100
dam
p
er resistance
– 1
10 =
100
dam
p
er resistance
– 1
0.06 IN. WC
DROP
0.55 IN.WC
DROP
C1497
9
100 – 9
= 10% of series resistance
Characteristic ratio =
total resistance – damper resistanc
e
dam
p
er resistance
=
total resistance
dam
p
er resistance
– 1
29
100 – 29
= 41% of series resistanc
e
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 36 by 64 in. (2304 in
2
) duct with an
airflow of 20,000 cfm and a pressure drop of 0.06 across a
parallel blade damper, determined the damper size as shown
in Table 5.

Honeywell AUTOMATIC CONTROL Specifications

General

Brand	Honeywell
Model	AUTOMATIC CONTROL
Category	Controller
Language	English