Siemens RCU50U, RCU50.2U Technical Instructions

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RCU50U and RCU50.2U

Room Temperature Controllers for
CAV Systems

Technical Instruction

Document No. 155-327P2

Rev. 1, March, 200

Description

Features

Application

RCU50U

The RCU microprocessor controlled CAV room controller is designed for air only, or air
and water heating and/or cooling systems. Controllers have proportional response.

• Modulating P-control

• 0 to 10 Vdc output for heating or cooling

• Automatic heating/cooling changeover (RCU50U)

• Manual heating/cooling changeover (RCU50.2U)

• Operating modes: Normal, Energy Saving, Frost Protection and Standby (RCU50U)

• Operating modes: Normal and OFF (RCU50.2U)

• Active 0 to 10 Vdc input for set point shifting (RCU50U)

• Operating mode changeover input for remote control (RCU50U)

• Adjustable minimum limitation for cooling output (RCU50U)

• Operating voltage 24 Vac

Controlling individual room temperature in HVAC installations that are heated or cooled
Controlling these types of equipment:

• Valve actuators

RCU50.2U

• Air damper actuators

Product Numbers

Product Numbers Features

NOTE:

Table 1.

RCU50U Without operating mode selector

RCU50.2U With manual heating/cooling changeover switch

To order without logo, change suffix to "/U/NL".

Example:

Siemens Building Technologies, Inc.

RCU50/U/NL.

Technical Instructions RCU50U and RCU50.2U Room Temperature Controllers

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Document Number 155-327P25 for CAV Systems
Rev. 1, March, 2002

Ordering

The temperature sensor, changeover mounting kit, and valve and damper actuators
must be ordered separately.

Table 2. Equipment Combinations.

Function

Heating-Cooling with
Minimum Limitation
Cooling

Product Numbe

Description Technical Instructions

QAH11.1 Temperature sensor 155-329P25

GDE16… 44 lb-in NSR Air damper actuator

155-187P25

GLB16… 88 lb-in NSR Air damper actuator
SSB61U Valve actuator 155-192P25

SSC61U

Valve actuator 155-313P25
SSC61.5U
SQS65U

Valve actuator 155-190P25
SQS65.5U

The controller measures the room temperature with its integrated sensor and maintains
the set point by delivering 0 to10 Vdc control commands. The RCU50U and RCU50.2U
provide P-control. With the RCU50U, the proportional band can be 2°F or 7°F (1°C or
4°C) in heating mode and 1°F or 3.5°F (0.5°C or 2°C) in cooling mode (selectable with
DIP Switch No. 4). With the RCU50.2U, the proportional band is fixed, 7°F (4°C) in
heating mode and 3.5°F (2°C) in cooling mode.

• RCU50U – When in the heating mode, on increase in temperature, the output signa
goes down (Reverse Acting - R.A.) from 10 to 0 volts. When in cooling mode, on
increase in temperature, the output signal goes up (Direct Acting - D.A.) from 0 to 1
volts.

• RCU50.2U – The output signal can be reversed 0 to 10 or 10 to 0 volts via the DIP
switch.

Y10 [%] Y10 [%]

100

c/o

100

T Room temperature
Y10 Output percentage
W Room temperature set point
XpH Proportional band heating

TH0577R1

0

XpKXpH

W

VR

T [˚F]

XpK Proportional band cooling
VR 0 to 100% minimum limitation of
cooling output
c/o Changeover

Figure 1. RCU50U Function Diagram.

Heating-Cooling

Y10 [%]

100

0

TH0578R1

Figure 2. RCU50.2U Function Diagram.
Minimum Limitation of

Cooling Signal

RCU50U

Using the potentiometer located on the circuit board, the cooling signal output can be
limited to a minimum value of between 0 and 100%. This can be used to ensure a
minimum supply air volume. When used in connection with a VAV controller, this
setting must be taken into account. To set minimum limitation, use a screwdriver to
adjust the potentiometer (see Figure 3). Values on the scale are percentage of full
operation.

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Siemens Building Technologies, Inc.

c/o

Y10 [%]

100

T Room temperature
Y10 Output percentage
W Room temperature set point
XpH Proportional band heating
XpK Proportional band cooling
c/o Changeover

XpH

0

XpK

W

T [˚F]

RCU50U and RCU50.2U Room Temperature Controllers Technical Instructions

c

For VAV Systems Document Number 155-327P25
Rev. 1, March, 2002

Minimum Limitation of
Cooling Signal,
Continued

Figure 3. Potentiometer Location (RCU50U).

Inversion of Output
Signal

RCU50.2U

Set Point Shifting

RCU50U

With the RCU50.2U, the output signal can be inverted with the help of DIP Switch
No. 1. If set to ON, 0V corresponds to 0% travel and 10V to 100% travel. In position
OFF, 0V corresponds to 100% travel and 10V to 0% travel.

Signal Input 1 and 2 is used for outside temperature compensation. Using a 0 to 10 Vd
signal, the set point can be shifted by ±22.5°F at 72°F set point. The neutral position is
at 5 Vdc and means no set point shift.

Q(%)

heating cooling

100

W Original set point
W1 Highest set point at 10V input
W2 Lowest set point at 0V input
set point shift

72ºF

0

Set Point Shift (K)

TH0621R1

Figure 4. Set Point Shifting (RCU50U).
Automatic Changeover

RCU50U

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

W2 W1

22.5ºF

0

22.5ºF
1

W

22.5ºF 22.5ºF

5

(72ºF)

10

T [ºF]

Input Voltage (V)

(V) Input voltage

temperature is above 82°F (28°C), the controller switches to heating mode; below
61°F (16°C) it switches to cooling mode.

CM

HM

TH0579R1

Siemens Building Technologies, Inc.

M

61

(16)82(28)

Figure 5. Automatic Changeover Mode.

˚

(˚C)

CM Cooling mode
HM Heating mode
M Operating mode
T

Water temperature

W

T

W

F

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Technical Instructions RCU50U and RCU50.2U Room Temperature Controllers

o

Document Number 155-327P25 for CAV Systems
Rev. 1, March, 2002

Set Point Limit Stops

The room temperature set point can be limited in increments of 2°F (1°C) by using the
minimum and maximum set point limit stops. This prevents arbitrary set point
readjustments.

To set limit stops, remove the set point knob by pulling it straight off the shaft.
Reposition gray tabs for high and low stops in the holes around the perimeter of knob
as required. See Figure 6.

65

7

0

2

0

60

15

55

10

50

L

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i

s

&

75

20

18

22

6

2

5

1

24

14

26

12

1

0

8

S

t

a

e

80

28

30

85ºF

30

Cº

f

a

Operating Modes

Normal Mode

Frost Protection Mode
(RCU50U)

Energy Saving Mode

Operating Mode
Changeover Switch

(RCU50U)

TH0625R1

Figure 6. Set Point Limit Stops.

When dry contact (D1 and Ground) is open, the set point knob setting takes over
control and normal mode is initiated.

Frost protection mode can be initiated by activating the external operating mode
changeover switch, if DIP Switch No. 1 is set to OFF.

If the room temperature falls below 46°F (8°C), the controller will automatically switch t
frost protection mode. In that case, the heating valve opens and the room temperature
is maintained at a set point of 46°F (8°C). The set point adjusted by the user will be
ignored.

Energy saving mode can be initiated by activating the external operating mode
changeover switch, if DIP Switch No. 1 is set to ON.

In energy saving mode, the heating set point is 61°F (16°C) and the cooling set point is
82°F (28°C), independent of the position of the set point knob.

A changeover switch can be connected to status input D1–GND. When the switch
closes its contact (caused by an open window, for instance), the operating mode
changes from normal operation or standby to energy saving mode (if DIP Switch No. 1
is set to ON), or from normal operation or energy saving mode to standby (if DIP Switch
No. 1 is set to OFF).

The operating action of the switch (N.C. or N.O.) can be selected.

Mechanical Design

The unit consists of two parts:

• Plastic housing which accommodates the electronics, the operating elements and
the built-in room temperature sensor.

• Controller base.

The housing snaps into the top and bottom of the mounting base.

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Siemens Building Technologies, Inc.