Controling my Boiler with my RPi

[Koos]

Hi to all

I have an Boiler type Vailant hw PRP CW4 VHR nc CW 4/3 and I want to control it with my RPi 2 B.

Can I use only an OpenTherm Gate or must I still connect my roomcontroller

Does somebody have an working solution?

Grz Koos

[marcelr]

Maybe this question was better asked in the OTGW thread.

First of all, I'm not sure if your boiler supports OpenTherm.

If it does, there are still some things to be resolved:
AFAIK the OTGW is not a thermostat in itself. This means that you will need a device that records room temperature, and has a control algorithm in it to calculate the boiler temperature setpoint, based on a room temperature setpoint, the actual temperature, and the specific thermal features of you home. Then it should be able to send this info to the boiler. Typically, such a device is called a room thermostat. If you can read room temp with your raspi, and you happen to have a thermostat algorithm as described above, then I think it could be done.

grtz,

marcelr

[ModbusMan]

Hi Marcel,

Any ideas on how to calculate the boiler temperature setpoint? Seems to be the "missing link" of domotica since can't find any info anywhere on the internet. (Unless I go and work for Rhema...)

Thnx,
ModbusMan

[marcelr]

That's on my list for the Christmas break. What we need is a control algorithm that takes care of long dead times, in combination with a PID controller.
In boilers, that's typically done with TPI control (a mixture of PI and bang-bang control).

Found a nice (more sophisticated) example the other day:

Control Engineering Practice 9 (2001) 1195–1208
Robust tuning procedures of dead-time compensating controllers
Ari Ingimundarson, Tore Hagglund*
Department of Automatic Control, Lund Institute of Technology, Box 118, S-221 00 Lund, Sweden

(with example code, in the Matlab control toolbox)
Will have to get my OTGW working, first, though. I soldered everything together, can run the tests, but when it's connected, my toon can no longer do OpenTherm ... that needs to be fixed first.

grtz,

marcelr

[ModbusMan]

Hi Marcel,

I also had another post running on this. (Opentherm - calculating boiler control setpoint).

I will look up the article you suggested. Only managed to find the spec. for OpenTherm v2.2 from 2003 which is probably good enough for now. I also built an OTGW and using Otmonitor can get a graph of the boiler controller setpoint compared to the room temperature setpoint, room temperature, boiler water temperature, relative modulation level and outside temperature as seen/set by my Remeha iSense thermostat. Data does show some kind of a pattern but also displays some irregular behaviour...

Hope you get your OTGW working soon.

grtx,
ModbusMan

[marcelr]

Will have to get my OTGW working, first, though. I soldered everything together, can run the tests, but when it's connected, my toon can no longer do OpenTherm ... that needs to be fixed first.

Done.

Connection: toon thermostat - toon boiler module - OTGW - EMS-OT converter - boiler.
(It's a bit of a Heath Robinson now, but it works)
Updated the OTGW firmware to the latest. It's up and running, get the right graphs, but no numbers in the logs ... will need to get that fixed.

EDIT: All software transferred to a headless raspi 2 B. Configured otmonitor properly, it's logging away happily.

First findings:

Status gets updated every 3 seconds, boiler water temp, return temp, relative modulation level, and control setpoint are updated every 12 seconds, the rest of the OT data every 85 seconds.

Control bandwidth will be limited by this 12 second interval (for me at least, other hardware may have higher update rates for these variables). No problem, we're looking at slowly varying systems.

grtz,

marcelr

[marcelr]

I will continue the control bit of this thread in this thread (it's not specific for RPi, and I will focus on Eneco's toon thermostat):

http://www.domoticaforum.eu/viewtopic.php?f=75&t=10664

grtz,

marcelr