Installation guide

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Recommended sensor locations
Sensor or transmitter location has a significant impact on
humidifier performance. In most cases, we recommend that you do
not interchange duct and room humidity devices. Room humidity
devices are calibrated with zero or little airflow; whereas duct
humidity devices require air passing across them.
Recommended sensor locations (see figure below):
A Ideal—ensures the best uniform mix of dry and moist air with
stable temperature control.
B Acceptable—room environment may affect controllability
such as when sensor is too close to air grilles, registers, or heat
radiation from room lighting.
C Acceptable—provides uniform mixture of dry and moist air,
but if extended time lag exists between moisture generation and
sensing, make sure control contractor extends sampling time.
D Acceptable—(behind wall or partition) for sampling entire room
if sensor is near an air exhaust return outlet. Typical placement
for sampling a critical area.
E Not acceptable—these locations may not represent actual overall
conditions in the space.
F Not acceptable—do not place sensors near windows, door
passageways, or areas of stagnant airflow.
G Best location for duct high limit humidistat or humidity sensor.
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Figure 25-1:
Recommended sensor location
Outside air
Relief air
Return air
Air handling
unit
8' to 12'
(2.4 m to 3.7 m)
min.
Humidifier dispersion assembly
Turning vanes
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transmitter on the lower corner of the inside surface of double-pane
window glass on north or northeast facing window
Window
Doorway
Window
Point of vapor absorption
Vapor absorption has taken place
Airflow switch (sail type) or differential
pressure switch recommended for VAV
applications)
High limit humidistat or high limit
transmitter (set at 90% RH maximum) for
VAV applications
Damper control
C
A
E
F
D
B
E
F
G
F
DC-1084
Other factors that affect humidity
control
Unsatisfactory humidity control may involve
more than the controller’s capability to
control the system. Other factors that play
an important role in overall system control
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to load
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moisture migration time lags
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transmitters and their location
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or duct
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and space environments
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VL3_IOM.pdf 29 11/19/2009 9:11:12 AM