User Manual

Siemens Building Technologies Application : 74 RWD32/74 – 04.2001
HVAC Products RWD32 2
The main sensor senses the supply air temperature and on a rise in temperature
the RWD32 via Q1, Q2 digital outputs modulates the three position cooling valve
as determined by the cooling set point and proportional band settings.
The auxiliary temperature sensor (X2) senses the outside air temperature, and
adjusts the supply air temperature setpoint as per the temperature shift program
set up in the controller.
Three position control has no feedback from the valve actuator to determine it’s
position, so the timing of the actuator must be known to the controller. During
commissioning the actuator timing must be entered. A common actuator timing for
small three position valve and damper actuators is 150 seconds from fully open to
fully closed, so this means that the controller modulates the actuator over the Xp
proportional band range for 150 seconds.
E.g. An Xp proportional band of 4º C and 150 second cycle time means that for a
4º C change the controller will drive the actuator for 150 seconds.
A synchronous check on the position of the actuator is carried out on a regular
basis.
Cooling sequence
Load
Setpoint
Cooling
0%
100%
Q
2
Q
1
Xp
Valve
Opening
Actuator timing
L
S1
D1
N
BM
X1 X2MM
X1
M
G AC 24 V
Q12 Q14
RWD32
Q11
Q22 Q24
Q21
Q1 Q2
N1
TOOL
PC
G
(L) AC 230 V
N
Y1 Y2
N
GO
CCV
BM
X2
RWD32
N1 RWD32 controller
X1 Main temperature sensor
X2 Outside air temperature sensor.
S1 Time clock or switch
Q1 Opening contact for 230Vac 3 - position control valve
Q2 Closing contact for 230Vac 3 - position control valve
CCV 3 – position 230Vac chilled water control valve
PC Personal computer
Description of operation
Function diagram
Connection diagram