Technical Instructions
RDF20U Room Temperature Controller with LCD
Document Number 155-334
for Two-Pipe Fan Coil Units with Electric Heat
September 27, 2007
Page 2
Siemens Industry, Inc.
Accessories
ARG70
Adapter plate for 4-inch × 4-inch or 2-inch × 4-inch conduit boxes
141-570
Lockable thermostat guard
QAH11.1
Changeover/remote temperature sensor
Warning/Caution
Notations
WARNING:
Personal injury or loss of life may occur if you do not perform
a procedure as specified.
CAUTION:
Equipment damage may occur if you do not follow a
procedure as specified.
Operation
The controller acquires the room temperature via its integrated sensor or optional
external return air temperature sensor (QAH11.1) and maintains the setpoint by
delivering two-position valve control and electric heat output commands.
The switching differential is 2 K (3.6
F) in Heating mode and 1 K (1.8
F) in Cooling
mode (adjustable).
Fan Operation
The fan is switched to the selected speed via control output 12, 11 or 10.
When
the “Temperature-dependent fan control“ function is activated (can be selected
with DIP Switch No. 1), the fan is switched on/off depending on the temperature,
together with the valve.
It is switched off when any of the following occurs:
•
leaving the heating or cooling sequence, provided the “Temperature-dependent fan
co
ntrol“ function is activated.
•
manually changing to Standby “ ” provided no setpoints (example, for freeze
protection) are set and active.
•
activating an external operating mode changeover switch, provided application
conditions do not call for Economy mode.
•
turning off the controller’s power supply.
NOTE:
To avoid overheating the electric heat or to prevent the thermal cut-out from
responding, the fan will overrun for 60 seconds (default Parameter 21) when
the electric heat is switched off.
CAUTION:
In the event of failure, the RDF20U cannot protect the electric heat against
overheating. Therefore, the electric heat must be equipped with a separate
safety device (high temperature detection thermostat).
Display
If DIP Switch No. 2 is set to ON (factory setting), the controller displays the measured
room or return air temperature (unless parameters or setpoints are temporarily
changed). If the DIP switch is set to OFF, the controller displays the Normal operating
mode setpoint. In this case, the value of the current temperature reading can only be
visualized temporarily by selecting Parameter P14.
