I gather that Daikin has four different control protocols, and most devices include only one:
- S403 (aircons?)
- S21 (aircons)
- F1/F2 (large scale)
- P1/P2 (small scale domestic)
It can be hard to work out which interface each device has. I have an Altherma LT (EHBH08CB), so I’m mainly interested in controlling that. It has a P1/P2 interface (the only one of these four which is mentioned in the Installer manual).
The Daikin Control Systems catalogue lists a number of Modbus (RS485) interfaces and the devices which they are compatible with (on page 132). I’m surprised that the Altherma HT and LT have different interface units (RTD-W and RTD-LT/CA respectively), given that both have P1/P2 interfaces. I suspect this has something to do with the additional non-Modbus controls on these units (e.g. resistance and voltage control of fan speeds, which would only apply to an aircon unit) and that the Modbus part of these interfaces might be identical, but I’m not sure.
Given one of these interface units, attached by a pair of wires to the P1/P2 connector on the hydrobox/indoor unit (in parallel with the built-in controller), one should be able to connect a PC, Raspberry Pi or Arduino to the Modbus interface (with a suitable adaptor) and read all sensors (and change all settings) from there.
From the above answers, it seems that a BRP069A61/62 LAN controller may provide an easier interface (HTTP/websockets), and also integrate with a PV system (without extra programming). However it requires a wired LAN connection (not wi-fi), which I don’t have anywhere near the hydrobox. A powerline network would probably work, but less reliably.
There is some documentation of the RTD-W’s Modbus registers here. I would expect the RTD-LT/CA to have similar registers, as the hydrobox/indoor unit functions are very similar.
The Control Systems catalogue (page 133) says that the flow rate can be monitored by Modbus using the RTD-LT/CA (for Altherma LT), but not using the RTD-W (for Altherma HT).