WT-4000 Series Pneumatic-to-Direct Digital Control (DDC) Room Thermostats Installation Instructions
13
Operation
The WT-4000 Series Pneumatic-to-DDC Room
Thermostats are regulated by a number of operational
modes that can be triggered by inputs such as changes
in inside and outside environments, data received from
other sensing devices, and scheduled times. Each
mode is designed to optimize energy use under certain
conditions, and has a set of rules that manages
operation of HVAC equipment and restricts local room
thermostat requests.
The two types of operational modes are scheduled and
manual. Scheduled modes are triggered by occupancy
schedules, and provide energy savings by aligning the
operation of HVAC equipment to the actual building
occupancy. Manual modes are initiated by the user at
the room thermostat level, and adjust the operation of
HVAC equipment manually outside of the schedule, but
within set energy policy parameters.
The WT-4000 Series Room Thermostats are designed
to support any 0 to 22 psig (0 to 152 kPa) pneumatic
HVAC control system. Variation in branch line pressure
is proportional to the deviation of room temperature
from the setpoint. The proportional factor is determined
by the gain/sensitivity, which is defined as the change
in branch line pressure in psi (kPa) in response to a 1F°
(0.6C°) change in room temperature.
Figure 15 illustrates the linear relationship between
branch line pressure and room temperature, at a given
setpoint for a Direct Acting (DA) room thermostat
configuration. For a Reverse Acting (RA) room
thermostat configuration, the graph is inverted
horizontally.
Figure 15: Branch Line Pressure vs. Room Temperature
Gain/
Sensitivity
Setpoint
Pressure
FI
G
:brn
ch
_
ln
_pr
ss
r
Set-
Point
Half of the
Proportional Band
Half of the
Proportional Band
1F
° (
0
.6
C
°)
1F°
(0.6C°)
Dead Zone
±1F° (±0.6C°)
Temperature, °F (°C)
B
ra
n
c
h
Li
ne
P
re
s
s
u
re
,
p
si
g (
k
P
a)
