RDU20U, RDU50U and RDU50.2U Room Temperature Controllers
Technical Instructions
with LCD for Heating and Cooling Systems
Document Number 155-735
November 1, 2006
Siemens Industry, Inc.
Page 3
Function, Continued
RDU50U and RDU50.2U
Figure 2. Heating Mode, RA.
(DIP Switch 2 in ON Position)
Figure 3. Cooling Mode, RA.
(DIP Switch 2 in ON Position)
Figure 4. Heating Mode, DA.
(DIP Switch 2 in OFF Position)
Figure 5. Cooling Mode, DA.
(DIP Switch 2 in OFF Position)
T
Room temperature
XpH Proportional band heating
XpK Proportional band cooling
W
Room temperature setpoint
Y
Out
Output percentage
NOTE:
The diagrams only show the proportional part of the P+I controller.
Automatic Changeover
RDU50U and RDU20U
The water temperature measured by the changeover sensor (QAH11.1) is used by the
controller to switch from heating to cooling mode, or vice versa. When the water
temperature is above 82°F (28°C), the controller switches to Heating mode; below
61°F (16°C), it switches to Cooling mode.
If immediately after switching on, the temperature is between the two changeover
points, the controller will start in Heating mode. The medium temperature is measured
at half-minute intervals and the operational status updated. The value of the current
temperature reading and the mode can be visualized temporarily by selecting
parameter P14.
In systems without automatic changeover, the temperature sensor can be replaced by
an external switch for manual changeover. In systems with continuous heating mode,
no sensor will be connected to the controller’s input. With continuous cooling mode, the
controller changeover input must be bridged.
CM Cooling mode
HM Heating mode
M
Operating mode
T
W
Water temperature
Figure 6. Automatic Changeover Mode.
