Installation guide

9
SENSING DEVICE PLACEMENT AND WIRING
OPTION: Aquastat
This option protects the humidifier from damage due to
freezing. Should the temperature of the water in the
humidifier drop to near freezing the aquastat will energize
the heat source as needed.
OPTION: High Limit Controller
This option is recommended for all duct humidifier
applications. It is usually set for 90 to 95% RH and
protects the duct system from condensation due to a rise
in duct RH or drops in air temperature or air volume.
On/Off Humidistats*
DRI-STEEM may provide three types of on-off controls:
a wall or a return air, duct mounted humidistat, or a
pneumatic/electric relay.
Modulating Humidistats*
Humidistats can be supplied for either wall or duct
mounted applications. These humidistats are powered by
a 21 VDC supply provided by the VAPOR-LOGIC
2
control
board. A 0-15 VDC modulated control signal is returned
to the VAPOR-LOGIC
2
control board which modulates the
output of the humidifier.
To use a signal from a pneumatic humidistat,
DRI-STEEM can provide a transducer for a 3-20 psi
pneumatic input range. This pneumatic input is con-
verted to a 0-135 ohm signal. This 0-135 ohm signal is
adaptable to the VAPOR-LOGIC
2
control board.
*Humidity set-point is made at the humidistat.
Modulating Humidity Sensors with Transmitters
DRI-STEEM can supply sensors with transmitters for
either wall or duct mounted applications. They are
powered by VAPOR-LOGIC
2
and have an output of 4-20
mA and a 0-100% RH range. (Humidity set-point is done
at the VAPOR-LOGIC
2
keypad.)
OPTION: Variable Air Volume (VAV) Control Kit
When this system is ordered, a second modulating
humidity sensor with transmitter is supplied (for duct
mounting). This transmitter limits humidifier output during
periods of low air flow to prevent saturation of air being
humidified.
NOTE: The wiring diagram (found on the inside of
the humidifier control cabinet) will show proper
wiring for these controls.
Figure 9-1: Shielded cable
OM-311
OPTION: Cold Snap RH Offset
This option prevents condensation from forming on
windows during periods of frigid weather. It consists of a
temperature sensor with transmitter mounted on an
appropriate window to sense glass temperature. When the
glass temperature falls below the dew point, the RH set
point is automatically lowered. When the cold snap ends
and the glass temperature rises, the normal RH setpoint is
automatically restored.
Cold Snap Transmitter Placement (See figure 10-1.)
1. Position the cold snap transmitter control box
on a wall adjacent to lower window framing and
route the temperature sensor umbilical cord
behind the wall and out through window
framework.
2. Place the flat surface of the temperature
sensor tip on the lower corner of the glass
surface.
3. Temporarily hold the sensor tip in place with
strips of masking tape.
4. Apply a small amount of clear RTV silicone
adhesive over and around the sensor tip
(making sure the sensor tip is in contact with
the window glass).
5. After adhesive has cured, remove masking
tape.
Temperature
Transmitter
Shielded Cable
Sensor
Tip
T+
T-
VAPOR-LOGIC
2
Note: DRI-STEEM recommends using #18 gauge
plenum rated shielded cable for transmitter wiring
and grounding shield at a common point in control
cabinet. (See figure 9-1.)