Siemens RAB20 Series Technical Instructions

RAB20 Series

Two-pipe Fan Coil Room
Thermostat with Automatic
Changeover

Technical Instructions

Document No. 155-526P25

ET RAB-2

March 2, 2007

RAB20.1

Description

Features

Application

Two-wire, gas diaphragm-based fan coil room thermostat for heating or cooling
systems with two-pipe fan coil applications.

•

Automatic changeover

•

Manual, three-speed fan switch

•

Fan release function

•

Dual setpoint temperature scale

•

Two-point control algorithm (On/Off)

•

24 to120 Vac, 277 Vac operating voltage

•

Two mounting styles: electrical wall box or drywall

•

Wall plate adapter (ARG70) included with electrical wall box mount styles

The RAB20… is used in heating or cooling systems with external automatic
changeover devices (aquastats) to maintain the selected room temperature.

Typically used in commercial, high-rise and light industrial buildings in conjunction with:

•

Zone valves

•

Thermal valves

• Fans

•

Aqua sensors (changeover sensors, provided by others)

Product Numbers
Accessory
Technical Design

See Table 1.
ARG70 Wall box adapter
The RAB20… fan coil room thermostat is based on a two-wire, gas diaphragm

technology.

Siemens Building Technologies, Inc.

Technical Instructions RAB20 Series Two-pipe Fan Coil Room Thermostat
Document Number 155-526P25
March 2, 2007

Operation

Heating Mode
Cooling Mode

Fan Speed

Fan Release Setting

Ventilation

Changeover

If the room temperature falls below the selected setpoint, the heating contact is closed.

If the room temperature rises over the selected setpoint, the cooling contact is closed.
The fan control speed can be controlled two ways:

• Manually, using the three-speed fan switch on the thermostat cover for continuous
operation.

(Low), (Medium), (High).

• Automatically, by switching to the selected fan speed using the thermostat for
controlled operation. Prior to commissioning, the jumper position corresponding to
the thermostat function must be selected.

There are three jumper position choices on the printed circuit board:

SR1
SR2
SR3

Auto
Auto

When the ventilation function (

Select fan speed as continuous operation

Fan is switched with the cooling valve
Fan is switched with the heating valve

) is selected (on the RAB20.1.. only), the heating and

cooling contacts are always open and the fan works at the selected speed.
Heating/cooling changeover is automatic, based on room temperature. Changeover is

achieved externally using an SPDT aqua sensor (not included) wired between
Terminals W, Y and the zone valve to change switch action.

Adjustments

The required temperature can be selected by a rotating setpoint adjuster on the front of
the thermostat.

High and low setpoint limit stops can be engaged to limit temperature range.

Table 1. Product Numbers.

Mounting Style Product

Description

Number

Electrical Wall

Box (with wall

box adapter)

RAB20UW

RAB20.1UW

Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover

Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover; fan only
function

Drywall

RAB20U

Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover

RAB20.1U

Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover; fan only
function

Page 2 Siemens Building Technologies, Inc.

RAB20 Series Two-pipe Fan Coil Room Thermostat Technical Instructions
Document Number 155-526P25
March 2, 2007

Warning/Caution Notations

WARNING:

Specifications

Ambient Conditions

Wiring

Housing

Agency Certification

Operating voltage 24 to 120 Vac, 277 Vac
Frequency 50/60 Hz
Setpoint adjustment range 50°F to 85°F (10°C to 30°C)
Setpoint limit stops Adjustable
Switching differential (SD) ≤1.8°F (1°C), fixed
Switch rating 6A RES, 3.5A FLA, 12A LRA
Switch action Single-Pole, Double-Throw (SPDT)
Output 2-position (On/Off)
Weight 5 oz. (0.14 kg)
Dimensions 3.80 × 4.45 × 1.68 inches

(96.4 × 113.1 × 42.8 mm)
Color Ivory white with gray selector knobs
Operation

Temperature 32°F to 122°F (0°C to 50°C)
Relative humidity <95%

Transport/Storage

Temperature –4°F to 122°F (–20°C to 50°C)
Relative humidity <95%

Screw terminals for wires of 2 × 16 AWG
or 1 × 14 AWG
minimum 20 AWG

Material Plastic
Enclosure rating NEMA1
Bellows Environmentally-friendly gas

Conforms to CE requirements
UL listed to 873 (E35918)
cUL listed to Canadian standard
C22.2 No. 24-93

Personal injury, or loss of life may occur if you do
not perform a procedure as specified.

Part Number Description Technical Instructions

SFA71U 24V NC
SFA11U 120V NC
SFA208V/25 208V NC
SFA277V/25 277V NC
FTA71 24V NC 155-109
599 Series Zone

Valves

Siemens Building Technologies, Inc. Page 3

Table 2. Control Valves.

Two-way

Three-way

155-521

155-320P25