13
CRUV INSTALLATION, OPERATION, AND MAINTENANCE MANUAL
Sensor placement
INSTALLATION
SENSOR LOCATION IS CRITICAL
Sensor location has a signifi cant impact on humidifi er performance. See the
recommendations below and Figure 13-1.
Note: DriSteem recommends that you do not interchange room and duct
humidity devices. Room humidity devices are calibrated with zero or
little airfl ow, whereas duct humidity devices require air passing across
them.
Recommended humidity control (transmitter/humidistat) locations:
A
Ideal. Ensures the best uniform mix of dry and moist air with stable
temperature control.
B
Acceptable, but room environment can 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. If extended time
lag exists between humidity generation and sensing, extend 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 might not represent actual overall
conditions in the space.
F
Not acceptable. Do not place sensors near windows, door passageways,
or areas of stagnant airfl ow.
Recommended safety (airfl ow and high limit) sensor location:
G
Best sensing location for high limit humidistat or humidity sensor and airfl ow
proving switch.
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Outside air
Relief air
Return air
Air handling
unit
8' to 12'
(2.4 m to 3.7 m)
min.
Humidifi er dispersion assembly
Turning vanes
Window
Doorway
Window
Point of vapor absorption
Vapor absorption has taken place
Airfl ow 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
E
F
G
F
DC-1084M
Wall or
partition
Other factors affecting humidity control
Humidity control involves more than the
controller’s ability to control the system. Other
factors that play an important role in overall
system control are:
• Size of humidifi cation system relative to load
• Overall system dynamics associated with
moisture migration time lags
• Accuracy of humidistats and humidity
transmitters and their location
• Dry bulb temperature accuracy in space or
duct
• Velocities and airfl ow patterns in ducts and
space environments
• Electrical noise or interference
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mc_060508_0750
Temperature compensation option: Place a temperature compensation
sensor on the lower corner of the inside surface of double-pane window
glass on north- or northeast-facing window.
FIGURE 13-1: RECOMMENDED SENSOR LOCATIONS
