ASHRAE Journal - August 2019 - 58

COLUMN ENGINEER'S NOTEBOOK

one that causes the FSD to fully
FIGURE 5 Wiring of reopenable FSDs.
close (by zeroing the actuator input
signal). The "fire-stat" (aka "electronic fusible link") is the high
165°F
250°F
120V
limit thermostat provided with the
1 Hot
Standby
FSD to close the damper (actua2 Neutral
Power
tors are spring-return, fail-closed)
when air temperature exceeds the
Closed
fire-stat setpoint, typically 165°F
Open
(74°C) but usually increased to
250°F (121°C) for FSDs used for
Fire/Smoke Damper
smoke exhaust. The FSD must be
FAS
FAS
FAS
FAS
on standby power (like all FSDs
Command Status Status
Command
Closed Open
Reopen
Open/Close
used for smoke control) and a
transformer is required because
Fire Alarm System
120V modulating actuators are
not available. FSDs with available
airfoil blades, opposed blade action, and modulating
FSDs (e.g., area detection) so DSDs are not always
actuators control airflow exactly the same as a stanrequired. But regardless who provides the DSD, the
dard modulating damper, so there is no value to using designer must ensure that it is compatible with the
separate FSDs and control dampers in series.
air velocities that can be expected through the FSD.
In almost all cases, this means the DSD must function
Using FSDs as Balancing Dampers
with zero velocity since most systems shut off during
FSDs can also be used as balancing dampers where the unoccupied hours (zero airflow). Even 24/7 systems
damper is partially closed to deliver the desired airflow
can have very low airflow rates if they are VAV with
rate during normal operation then fully opened by the
low minimum airflow setpoints.5 So sampling tubetype DSDs can seldom be applied to FSDs since they
FAS for smoke control (e.g., smoke exhaust) duty. The
typically have a minimum velocity requirement of
classic example is exhaust from corridors in high-rise
200 to 300 fpm (1 to 1.5 m/s).
residential buildings: during normal operation, air is
exhausted equally from each floor, but for smoke conReopenable FSDs
trol mode, only the "fire floor" is exhausted at a high
Almost all FSD manufacturers have an option using
exhaust rate. For this duty, the FSD would have a modutwo fire-stats, one to close the damper at a relatively
lating 24V actuator with a built-in potentiometer, often
low temperature, e.g., 165°F (74°C), and a separate one
called a 3-position actuator (fully open, fully closed,
closing the damper at a higher temperature, e.g., 250°F
and partially open as determined by the potentiometer
(120°C), allowing the FAS (usually through manual fireadjusted during system balancing). Wiring is similar to
fighter control overrides) to reopen the damper if air
Figure 4 with a transformer and three wires for the three
temperature first rises above the low temperature limit
positions.
but is below the high temperature limit. This requires a
FSD Smoke Detectors
non-standard 3-wire connection from the FAS as shown
Factory installed duct smoke detectors (DSDs) are
in Figure 5. To the author's knowledge, there is no code
available from most FSD manufacturers, but, at least
that requires this additional control, and unless it is well
in the area where the author practices, they are selcoordinated with the FAS design, installation errors can
dom used because the smoke detectors usually are
occur.
required to be compatible with the FAS, often propriThe author had a project where the FSDs were proetary and not always available from FSD manufactur- vided with dual fire-stats, one for 165°F (74°C) and
ers, and also because there are other ways to control
one for 350°F (177°C) (the FSD's maximum rated
58

ASHRAE JOURNAL

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ASHRAE Journal - August 2019

Table of Contents for the Digital Edition of ASHRAE Journal - August 2019

Contents
ASHRAE Journal - August 2019 - Intro
ASHRAE Journal - August 2019 - Cover1
ASHRAE Journal - August 2019 - Cover2
ASHRAE Journal - August 2019 - 1
ASHRAE Journal - August 2019 - Contents
ASHRAE Journal - August 2019 - 3
ASHRAE Journal - August 2019 - 4
ASHRAE Journal - August 2019 - 5
ASHRAE Journal - August 2019 - 6
ASHRAE Journal - August 2019 - 7
ASHRAE Journal - August 2019 - 8
ASHRAE Journal - August 2019 - 9
ASHRAE Journal - August 2019 - 10
ASHRAE Journal - August 2019 - 11
ASHRAE Journal - August 2019 - 12
ASHRAE Journal - August 2019 - 13
ASHRAE Journal - August 2019 - 14
ASHRAE Journal - August 2019 - 15
ASHRAE Journal - August 2019 - 16
ASHRAE Journal - August 2019 - 17
ASHRAE Journal - August 2019 - 18
ASHRAE Journal - August 2019 - 19
ASHRAE Journal - August 2019 - 20
ASHRAE Journal - August 2019 - 21
ASHRAE Journal - August 2019 - 22
ASHRAE Journal - August 2019 - 23
ASHRAE Journal - August 2019 - 24
ASHRAE Journal - August 2019 - 25
ASHRAE Journal - August 2019 - 26
ASHRAE Journal - August 2019 - 27
ASHRAE Journal - August 2019 - 28
ASHRAE Journal - August 2019 - 29
ASHRAE Journal - August 2019 - 30
ASHRAE Journal - August 2019 - 31
ASHRAE Journal - August 2019 - 32
ASHRAE Journal - August 2019 - 33
ASHRAE Journal - August 2019 - 34
ASHRAE Journal - August 2019 - 35
ASHRAE Journal - August 2019 - 36
ASHRAE Journal - August 2019 - 37
ASHRAE Journal - August 2019 - 38
ASHRAE Journal - August 2019 - 39
ASHRAE Journal - August 2019 - 40
ASHRAE Journal - August 2019 - 41
ASHRAE Journal - August 2019 - 42
ASHRAE Journal - August 2019 - 43
ASHRAE Journal - August 2019 - 44
ASHRAE Journal - August 2019 - 45
ASHRAE Journal - August 2019 - 46
ASHRAE Journal - August 2019 - 47
ASHRAE Journal - August 2019 - 48
ASHRAE Journal - August 2019 - 49
ASHRAE Journal - August 2019 - 50
ASHRAE Journal - August 2019 - 51
ASHRAE Journal - August 2019 - 52
ASHRAE Journal - August 2019 - 53
ASHRAE Journal - August 2019 - 54
ASHRAE Journal - August 2019 - 55
ASHRAE Journal - August 2019 - 56
ASHRAE Journal - August 2019 - 57
ASHRAE Journal - August 2019 - 58
ASHRAE Journal - August 2019 - 59
ASHRAE Journal - August 2019 - 60
ASHRAE Journal - August 2019 - 61
ASHRAE Journal - August 2019 - 62
ASHRAE Journal - August 2019 - 63
ASHRAE Journal - August 2019 - 64
ASHRAE Journal - August 2019 - 65
ASHRAE Journal - August 2019 - 66
ASHRAE Journal - August 2019 - 67
ASHRAE Journal - August 2019 - 68
ASHRAE Journal - August 2019 - 69
ASHRAE Journal - August 2019 - 70
ASHRAE Journal - August 2019 - 71
ASHRAE Journal - August 2019 - 72
ASHRAE Journal - August 2019 - 73
ASHRAE Journal - August 2019 - 74
ASHRAE Journal - August 2019 - 75
ASHRAE Journal - August 2019 - 76
ASHRAE Journal - August 2019 - 77
ASHRAE Journal - August 2019 - 78
ASHRAE Journal - August 2019 - 79
ASHRAE Journal - August 2019 - 80
ASHRAE Journal - August 2019 - Cover3
ASHRAE Journal - August 2019 - Cover4
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