FDP3-Modbus for AHU (Air Handling Units)

Operation modes

The AHU-modified FDP3-Modbus interface can operate in either of:

  • Full Capacity Control:
    • The AHU can only be switched On/Off and run in either Cooling (setpoint 18 DegC) or Heating (setpoint 29 DegC).
  • Demand Level Control:
    • The 'external' BMS system signals via Modbus a Demand Signal which is proportional to compressor speed using demand data.
    • The demand data processing is implemented in the 'external' BMS system.

ONLY control with Modbus is possible.

Custom algorithms are implemented with the 'external' BMS system and use any of above control modes. 

 

FDP3-Modbus-AHU Installation

When installing FDP3-BMS interfaces configured for AHUs (Air Handling Units) please follow the instructions below, as well as the instructions (FDP3-Modbus AHU Strategy Description) attached to this article. The instructions of the standard FDP3-Modbus interface are not valid and therefore will not work.

 

Mounting

The FDP3 interface can be mounted on DIN rails, or on a surface using screws of up to 5mm diameter.

Please contact Toshiba Technical Support for further details on mounting a FDP3 interface inside a Toshiba unit, as they as can advise you better on their products.

 

TCC-net AB network

TCC-NET Terminals A, B on the FDP3 interface connect to the Toshiba TCC-NET remote controller network. The polarity of the AB network is not critical (this means it would work either way around). The TCC-NET network is NOT the same as the A-B-C network.

*Note that the FDP3 is powered from this connection and communicates with the indoor unit on this network. Therefore, if the unit looses power the FDP3 interface will loose power too.

**Note: Please contact your distributor and Toshiba customer service for information regarding required quantity of FDP3 interfaces, their respective installation and the use of a wired remote controller.  

 

DIP switches and Operation modes

Set the DIP switches as described in the attached installation instructions to operate the FDP3-Modbus-AHU interface in the required operation mode.

 

RS485 network for Modbus communication

For control/monitoring with Modbus the RS485 network for Modbus communication must be used. Please read the article RS485 network requirements for further information.

 

Modbus

With Modbus indoor units' parameters can be controlled and monitored (see section below for further information). 

The FDP3-Modbus-AHU interface supports the Standard RTU Modbus protocol. Please see the FDP3-Modbus installation instructions for default Modbus communication parameters, as well as Modbus commands. If Baud rate and parity need to be changed then please follow this link for FDP3 baud rate and parity settings. 

The Modbus address is set as described on page 4 of the FDP3-Modbus interface installation instructions (click here for the FDP3-Modbus installation instructions).

The Modbus registers base is '0'. However, do note that some BMS systems shift the register addresses by '1'. 

 Note that we offer a software only for testing ModTool communication (see below).

For further information please see this article:

 

Status LEDs

The FDP3 LEDs signal various statuses during start-up, as well as during operation. 

  • LED 1: flashes on startup and while searching for the unit. Once communication with the AHU has been established LED 1 will remain solid ON.
  • LED 2: If a fault occurs LED 2 will be solid ON.
  • LED 3: Once communication over TCC-Net between FDP3 and indoor unit(s) has been established LED 3 should be flashing indicating that information is being exchanged between the FDP3 interface and the indoor unit(s).
  • LED 4 flashes when data is being exchanged over the RS485 line.

 

Controlling and Monitoring via Modbus

Use only the Modbus registers listed in the attached installation instructions (file: AHU Strategy Description) for controlling the unit.

For monitoring the input registers use the input registers as detailed in the (standard) FDP3-Modbus Installation Instructions (instructions attached - see Page 3). No further registers are available for monitoring.

The scaling note in the AHU Installation Instructions only refers to use with our free software ModTool (ModTool Communication with our Products).

*Note that the TA Return Air Temperature Sensor is fixed, because the Fixed Resistance in the TA sensor connection on the AHU1 interface must be left in place.

 

Faults

In the event of a fault LEDs 1 and 2 change their status as follows:
  • LED 1 is Off and LED 2 remains solid (On).

Faults can also be monitored via Modbus. For further information, please read Fault Detection with FDP3-Modbus.