26
VAPOR-LOGIC
®
VERSION 6 INSTALLATION AND OPERATION MANUAL
INSTALLATION
HUMIDISTAT AND SENSOR LOCATIONS ARE CRITICAL
Humidistat and sensor location have a significant impact on humidifier
performance . In most cases, 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 26):
A Ideal . Ensures the best uniform mix of dry and moist air with stable
temperature control .
B Acceptable, but 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 . If extended time
lag exists between moisture 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 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 sensing location for a high-limit humidistat or humidity transmitter and
airflow proving switch .
Outside air
Relief air
Return air
Air handling
unit
8' to 12'
(2 .4 m to 3 .7 m)
min .
Steam dispersion assembly
Turning vanes
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 .
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
E
F
G
F
DC-1084
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 humidification 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 airflow patterns in ducts
and space environments
• Electrical noise or interference
Step 1 – Field wiring: Sensor placement
FIGURE 26-1: RECOMMENDED SENSOR LOCATION
