Swegon CASA, HRV (FTX), rotary heat exchanger and MODBUS

Fresh air at home is very important ! For more than 15 years ago, at a major renovation of our house, we installed an HRV or in Swedish FTX system. Since then there have been nice updates for FTX equipment so when one of the fans was a little noicy and when the motor for the rotor died it was time to do an upgrade instead of repairing the old one. So we purchased an CASA R7 Genius(R7).

For me its important to get as much data as possible, to optimize energy consumption in our house, so despite that the the R7 have a nice app we also added a SEM interface to get the data, via MODBUS, that is available.

Intro

MODBUS

Swegon have choosen to use MODBUS RTU which is a serial RS 485 interface. For the Genius SW4.0 the register listing is found here. Please note the use of different register types according to the picture.

USB interface

In my case I choose the Waveshare USB to RS 485 converter to connect to my Raspberry Pi(RPi). 

Termination resistor

In a RS 485 network there schould be terminating resistors at each end of the network. With just 2 devices in the network both will be terminated. By deafult there is terminating resistor in the USB converter but in the SEM you have to move the jumper JP1 to the right position.

NodeRed

NodeRed(NR) is used, to get and display the data, and the nodes dashboard and modbus are added.

Implementation

Wireing

Just follow these instructions and connect the USB converter to your Master, RPi, or selected device.

NodeRed

Pick the "Modbus Read" node, edit it and set

"FC => FC 4: Read Input registers"

"Adress => 6201"

"Quantity => 5"

"Poll Rate => 2 => second(s)"

Create a new server with the default values

"Type => Serial"

"Serial port" is found via the search function

"Serial => RTU-BUFFERED"

"Baud rate => 38400"

"Unit-id => 1

save, add a debug node "Deploy", check the debug window and an array of temperatures will show. Check the register listing to se which.

Adding a chart node could show you the data as in the picture.

Remark

Function codes

Please note that NodeRed seems to follow MODBUS standard but 

• "Read Input registers" are refered to "FC 4" but Swegon have the reference "3x" as stated above.
• "Read Holding registers" are refered to "FC 3" but Swegon have the reference "4x" as stated above.
• Write to a Swegon "4x" register is done with a NodeRed "FC 6: Preset Single Register"

MODBUS protocol specification

Is found here