Specifications

DRI-STEEM CRUV Electric Humidifier Installation, Operation, and Maintenance Manual • Page 13
Humidistat and transmitter placement
Installation
mc_060508_0750
Humidistat and sensor locations are critical
Humidistat and sensor location have a significant impact on
humidifier performance. In most cases, do not interchanging 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, 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.
Figure 13-1:
Recommended sensor location
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