DRI-STEEM XT Series Electrode Steam Humidifier Installation, Operation, and Maintenance Manual • Page 13
Humidistat and transmitter locations are critical
Humidistat or transmitter location has a significant impact on
humidifier performance. In most cases, it is recommended 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 humidistat and
transmitter locations (see Figure 13-1):
A This is the ideal sensing location because this placement ensures the
best uniform mix of dry and moist air with stable temperature control.
B This location is acceptable, but the room environment may affect
controllability such as when the humidistat or transmitter is too close
to air grilles, registers, or heat radiation from room lighting.
C This location is acceptable because it provides a good uniform
mixture of dry and moist air, but if an extended time lag exists
between moisture generation and sensing, make sure the control
contractor extends the sampling time.
D This location behind a wall or partition is acceptable for sampling
the entire room if the sensor is near an air exhaust return outlet. This
location is also typical of humidistat or transmitter placement for
sampling a critical area.
E These locations are not acceptable because they may not represent
actual overall conditions in the space.
F These locations are not acceptable. Do not place humidistats or
transmitters near windows, door passageways, or areas of stagnant
airflow.
G This is the best location for a duct high limit humidistat or humidity
transmitter.
Figure 13-1:
Recommended humidistat and transmitter locations
Outside air
Relief air
Return air
AHU
8' to 12'
(2.4 m to 3.7 m)
minimum
Humidifier dispersion assembly
Turning vanes
Window
Doorway
Window
Point of vapor absorption
Vapor absorption has taken place
Airflow switch or differential pressure
switch (sail type 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
EF
G
F
Humidistat and transmitter
placement
Wall or
partition
DC-1084M
XT_IOM_Jan_2008.pdf 15 11/19/2009 10:13:34 AM
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