FCR015 Communicative controller for VAV damper, RS485

Communicative controller for VAV damper

2 x DI (presence, window), 2 x DO triac 24 V AC for thermic valves (heating, cooling) , 3 x AO 0..10 V (heating, cooling, VAV box), 1x Modbus slave / RS485 for SCADA/primary controller, 1x Modbus master / RS485 for UC095


FCR015 is a communicative controller of heating and cooling panels and a VAV (variable air volume) damper. It measures temperature and CO2 concentration in the room air using a room unit and it may either work autonomously, or be connected to a primary controller (MiniPLC or SoftPLC) or SCADA (RcWare Vision or any other SCADA able to act as Modbus master). As a room unit, UC905 is used.

  • Individual room control for systems with heating and cooling panels and VAV dampers

The controller communicates with a room unit UC905 over a dedicated bus (K2+, K2-). The room unit UC905 reads room temperature, CO2 concentration in the room air, setpoint correction by a knob, and operating status, which is selected by a short  push of the button or in the menu. Measured temperature range is 0 to +50 °C, CO2 range 0 to 2000 ppm. Read and entered values are processed in a PI (temperature) and proportional (CO2) control algorithm. On the output, there are analogue 0..10 V sequences to control the valve actuators and VAV controller.

The binary input DI1 switches between Comfort and Standby operating modes. The DI2 switches to Off mode.

The triac outputs DO1 and DO2 are controlled as PWM or 2-stage outputs copying the AO1 and AO2 sequences respectively. They also may be controlled over the bus as auxiliary outputs.

The controller incorporates real time clock with weekly scheduler (6 events per day). It switches between the Comfort, Precomfort, and Off operation modes. There is a binary presence input on the controller for access card reader, PIR sensor etc. Both NO and NC contact may be used, the selection follows in the configuration software. Each operation mode has separate setpoints for heating and cooling which are used as basis setpoints for setpoint calculation: to the basic setpoint, the manual setpoint correction is added, and the result is used as actual setpoint for heating or cooling.

The air volume setpoint (0..10 V output signal for the VAV controller) is derived from the CO2 concentration in the air, and operation status:


  • Comfort: the CO2 concentration is controlled with a proportional controller so as to achieve the setpoint (default is 800 ppm), with minimum air volume as set in a parameter of the configuration tool
  • Standby: there is minimum air volume required as set in the minimum air volume parameter
  • Off: the VAV output goes to 0 V.

Three LEDs indicate correct function: green (PWR) – power OK, red (TX1) – transmit data to the building bus, and red (TX2) – transmit data to the room unit. On the top there are four DIP switches: K1 bus end, and init switch to set factory defaults (Modbus address 1, communication 9600 bps, N, 8, 1).

The controller communicates with the management system over RS485 bus with Modbus RTU and therefore can be used in many control systems. See the variable list (Modbus table) in a separate document Room units and controllers  – Communication protocol description. Another bus, K2, communicates with the room unit. To configure and commission the controller use domat.exe, which is free to download at www.rcware.eu.