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Integration of Daikin air conditioning systems in Modbus

Description of the MB-LON gateway experience for Daikin air conditioner dispatching via Modbus RTU protocol

MB-LON Daikin DMS504B51 Modbus
Daikin Interface Gateway DMS504B51

Yesterday we completed the air conditioning testing phase of a building automation project at a private residence where several types of industrial networks (LonWorks and Modbus in this case) had to be interconnected.


The facility initially installed 20 Daikin air conditioning units, a Daikin DCS302CA51 central remote control, and a Daikin DMS504B51 interface gateway to integrate the system into the LonWorks network. However, the subsequently installed monitoring and control system used the Modbus RTU protocol.  To integrate networks among themselves, the designers chose the MB-LON gateway as the most budget-friendly solution.

The input data was the documentation of Daikin equipment, a map of Modbus registers made by the designers, and a list of air conditioner parameters corresponding to them. According to the assignment, each air conditioner had to have five input values for control and five output values for monitoring:

The total number of variables per air conditioner was 10. Accordingly, 200 variables were required to serve twenty air conditioners. Since the MB-LON gateway can handle up to one hundred variables, it was necessary to use two gateways for this system. The gateway is configured using the LonMaker package. In this project MB-LON is configured to work as a Slave device of the Modbus network.

The nciGatewayOpts variable, located in the Node Object function block, is used to configure the Modbus network parameters. It specifies the communication speed and the network address.

MB-LON block NodeObject
NodeObject block settings

Each variable (input and output) is served by its own function block. For the control variables these are FromModbus blocks (they correspond to the Holding Modbus registers), for the read variables - ToModbus (they correspond to the Input Modbus registers).  LonWorks variable type is selected in SCPTnvType property. Setting the correspondence between LonWorks variable and Modbus register is provided through configuration property SCPTlocation of each functional block.

MB-LON block FromModbus
FromModbus block settings
MB-LON block ToModbus
ToModbus block settings

For more information about the settings of each block, see the MB-LON documentation. As a result, the final design for the entire system looks as follows:

During the pre-commissioning stage some peculiarities of working with Daikin equipment were identified and taken into account, but in general the integration was smooth and at the moment the air conditioning system is put into normal operation.

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