Siemens RDU50U, RDU50.2U, RDU20U Technical Instructions

RDU20U, RDU50U and
RDU50.2U

Technical Instructions

Document No. 155-735

November 1, 2006

Room Temperature Controllers
with LCD for Heating and
Cooling Systems

RDU20U and RDU50U

RDU50.2U

Siemens Industry, Inc.

Description

The RDU Series Room Controller with LCD is designed for heating and cooling
systems.

Features

• Modulating Proportional + Integral (P+I) control

• Control depending on room or remote air temperature

• Output for a 0 to 10 Vdc actuator (RDU50U and RDU50.2U)

• Output for a floating (3-position) or on/off output actuator (RDU20U)

• Adjustable actuator run time (RDU20U)

• Automatic heating/cooling changeover (RDU20U and RDU50U)

• Manual heating/cooling changeover (RDU50.2U)

• Operating modes: Normal, Energy Saving and Off

• Operating mode changeover input for remote control

• Selectable installation and control parameters

• Adjustable minimum limitation for cooling output

• Optional selectable Direct Acting or Reverse Acting output

• Selectable display of room temperature or setpoint

• Fahrenheit or Celsius selectable

• Minimum and maximum setpoint limitation

• Operating voltage, 24 Vac

Application

• Individual room temperature control in heating or cooling HVAC applications.

• Control of that are heated or cooled.

Product Numbers

Table 1.

Product Numbers

Features

RDU20U

Automatic heating/cooling changeover

RDU50U

Automatic heating/cooling changeover

RDU50.2U

Manual heating/cooling changeover switch

Technical Instructions RDU20U, RDU50U and RDU50.2U Room Temperature Controllers
Document Number 155-735 with LCD for Heating and Cooling Systems
November 1, 2006

Page 2 Siemens Industry, Inc.

Accessories

ARG70 Adapter Plate for 4-inch × 4-inch conduit boxes
QAH11.1 Changeover/Remote Temperature Sensor
141-570 Lockable Thermostat Guard

Ordering

The temperature sensor, valves, and damper actuators must be ordered separately.

Table 2. Equipment Combinations.

RDU50U and

RDU50.2U

Product Number

Description

Technical

Instructions

SSB61U..

0 to 10 Vdc valve actuators

155-192P25

SSC61U..

155-313P25

SQS65U

SSC61.5U

SQS65.5U

155-190P25

GDE16…

44 lb-in NSR air damper actuators

155-187P25

GLB16…

88 lb-in NSR air damper actuators

155-187P25

RDU20U

SSB81U..

Floating control valve actuators

155-195P25

SSC61U..

155-314P25

SSC81U

SQS65.5U

155-308P25

GDE131…

44 lb-in NSR air damper actuators

155-187P25

GLB131…

88 lb-in NSR air damper actuators

155-187P25

All Models

Powermite MZ Series

Two-way globe zone valves

155-198P25

Powermite MZ Series

Three-way globe zone valves

155-199P25

Powermite MT Series

Two-way globe zone valves

155-196P25

Powermite MT Series

Three-way globe zone valves

155-197P25

Powermite 599 Series

Two-way ball valves

155-704P25

Function

The controller measures the room temperature with its integrated sensor or via a
remote return air temperature sensor (QAH11.1) and maintains the setpoint by
delivering continuous control commands to the actuators (0 to 10 Vdc [RDU50U and
RDU50.2U] or 24 Vac on/off, or three-position [RDU20U]). The controller provides P+I
control. The factory setting for the proportional band in heating mode is 3.6°F (2°C),
and in cooling mode 1.8°F (1°C) (adjustable). The integral action time is five minutes
(adjustable). Motor run time for the RDU20U is adjustable from 50 to 150 seconds in
10-second increments.

RDU20U

Figure 1. Heating/Cooling Modes.

C/O Changeover
P-band Proportional band
T Room temperature
W Room temperature setpoint
Y Y output percentage

NOTE: Diagram only shows

P-characteristic

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
YOut 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
TW Water temperature

Figure 6. Automatic Changeover Mode.