Control of boiler via Opentherm gateway from Rapberry Pi

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Control of boiler via Opentherm gateway from Rapberry Pi

Postby John@T4sLtd.co.uk » Sat Feb 10, 2018 10:49 pm

I've just has an Atag iC Economiser 35 installed which has an Opentherm interface.

I don't want to buy any off the shelf controls as I've written an open source BMS framework for some projects I'm doing with some universities.

I'd like to be able to turn the space heating on and off, and set the flow temperature from the Pi. I'd also like to able to set the domestic hot water temperature, though this is less important.

I see there is a gateway kit available from https://www.kiwi-electronics.nl/openthe ... it?lang=en with a pre-programmed PIC.

Am I likely to be able to use this kit with the standard firmware to interact with the boiler space heating ?

Are there any other interesting features or monitoring of the boiler I can do over this interface ?

Many thanks, J/.
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Re: Control of boiler via Opentherm gateway from Rapberry Pi

Postby marcelr » Mon Feb 12, 2018 8:35 am

John@T4sLtd.co.uk wrote:I've just has an Atag iC Economiser 35 installed which has an Opentherm interface.

I don't want to buy any off the shelf controls as I've written an open source BMS framework for some projects I'm doing with some universities.

Could you provide a link, please? Would be interested to have a look at that software.

John@T4sLtd.co.uk wrote:I'd like to be able to turn the space heating on and off, and set the flow temperature from the Pi. I'd also like to able to set the domestic hot water temperature, though this is less important.

I see there is a gateway kit available from https://www.kiwi-electronics.nl/openthe ... it?lang=en with a pre-programmed PIC.

Yes, and some other types. Forum member Cyril makes a very compact version for an orange pi zero:
https://www.domoticaforum.eu/viewtopic.php?f=75&t=11816
and there's a Nodo version as well:
https://www.nodo-shop.nl/en/opentherm-g ... teway.html

John@T4sLtd.co.uk wrote:Am I likely to be able to use this kit with the standard firmware to interact with the boiler space heating ?

It depends on what you want. In general, this OTGW is capable of talking to the boiler. It is NOT a thermostat, and has no control software on board. But you can set values for some parameters.
John@T4sLtd.co.uk wrote:Are there any other interesting features or monitoring of the boiler I can do over this interface ?
Many thanks, J/.

I am using this OTGW (with standard firmware) to monitor my boiler. It records the communication between boiler and thermostat. I have been using another one (with interface firmware, in combination with my computer and some dedicated software) to emulate a boiler, so as to be able to do some testing with a thermostat, without burning a single kg of gas. I think you need this version of the firmware (which is easily replaced), to make a raspberry pi or similar generate the OpenTherm boiler settings and then transfer them to the boiler through the OTGW.
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Re: Control of boiler via Opentherm gateway from Rapberry Pi

Postby John@T4sLtd.co.uk » Mon Feb 12, 2018 8:18 pm

>Could you provide a link, please? Would be interested to have a look at that software.

Hi marcelr,

It's early days for the BMS functionality. We have one system managing the heat store and scheduling of a biomass system, and seven which are are part of a PhD project linking ecohouses to import and export heat mains to control the scheduling of heating and heat import and export from/to the 10,000 litre central heat store. We've also used quite a bit for monitoring (non control) applications. There are some examples of data logged by this system linked in the document I hope I've managed to attach. User interfaces are currently limited, as is support for sensors and other devices. It's very much a framework which can be added to rather than a packaged solution. It's written in C++, but access to sensors is via IP address and port number, so any modules for sensor access could be written in any language.

The source hasn't been released yet, and could use a lot of tidying and documentation before it is, but when it is released, it will be under the Mozilla Public License Version 2.0

There is some documentation here: http://t4sustainability.co.uk/oBeMS/ which is a bit out of date, but gives an idea of what I'm trying to do. I suggest having a read of that, then asking some me questions. We can arrange a chat on the phone if you like.

Cheers, J/.
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Re: Control of boiler via Opentherm gateway from Rapberry Pi

Postby John@T4sLtd.co.uk » Mon Feb 12, 2018 8:36 pm

Marcelr wrote:
>John@T4sLtd.co.uk wrote:

>>Am I likely to be able to use this kit with the standard firmware to interact with the boiler space heating ?

>It depends on what you want. In general, this OTGW is capable of talking to the boiler. It is NOT a thermostat, and has no control software on board. But you can set values for some parameters.

I appreciate it's not a thermostat. What I'd like in essence is gateway which has an Opentherm interface on one side going to the boiler only, and an interface on the other side that can talk to a Rapberry Pi. The convention here seems to be to use the serial interface which is fine.

At a minimum I want to be able to send commands from the Pi to the boiler via the gateway to start and stop the space heating, and set the boiler central heating flow temperature and the domestic hot water temperature.

I think the mode of operation I want is described here under Stand-alone operation: http://otgw.tclcode.com/standalone.html#intro

Does this look sensible ?

Many thanks, J/.
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Re: Control of boiler via Opentherm gateway from Rapberry Pi

Postby John@T4sLtd.co.uk » Mon Feb 12, 2018 8:38 pm

I've never use PICs before. Given that I'll have to reprogram the PIC, what's the simplest PIC programmer it's worth getting ?

Cheers, J/.
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Re: Control of boiler via Opentherm gateway from Rapberry Pi

Postby marcelr » Mon Feb 12, 2018 10:52 pm

I think the PIC comes pre-programmed. Once programmed, you don't need a programmer to re-program it. It can be done on the mounted PIC, using the software from Schelte's website, without any extra handling of the device.

Kiwi electronics only sell the RS232 version of the OTGW, IIRC. And even then, you'll still need to do the soldering yourself. It's easily combined with a serial-to-USB adapter, though. One of mine (the monitor) is connected to a raspi3 in that way, and has been logging continuously for the last two years or so. If you buy this unit, be careful with the serial connection. The plug on the PCB and the sub-D connector may have a different numbering than what you would expect.

The standalone firmware gives you the possibility to send a series of commands/parameters to the boiler, not sure how many, I've never used this feature.

If you want full control over whatever you send to the boiler, you could use the interface firmware, and write the complete I/O from scratch. That's what I've done for boiler emulation in combination with a real thermostat. The code is somewhere on this forum, but I'll need to look for it. If you want to simulate a thermostat in combination with a real boiler, the procedures are pretty much the same, only the directions are reversed (and the command bits in the OT frames are different). The OTGW in this case just functions as an adapter that converts serial data to OpenTherm-compatible signals and vice versa. You will need to be a bit knowledgeable on the OpenTherm protocol in this case. A (rather old) version of the OT protocol is available from this forum.
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