Boiler with dual OpenTherm interface: recommended use?

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macfreek
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Boiler with dual OpenTherm interface: recommended use?

Post by macfreek »

Hi,

I have a Intergas Extreme 36 CW5, in a new home, currently with "dumb" thermostats. I like to add a smarter controller and consider the OTGW. However, this particular boiler has two OpenTherm interfaces, which are both needed(!). I think I have an idea how to make it work, but love to get some feedback!

First a little explanation of the boiler and dual OpenTherm. My home is relative new (build in 2018), and has (low temperature) floor heating downstairs, but regular (high temperature) radiators upstairs. Traditionally this is provided by a single pump and a heat exchanger between the two zones, that ensures that the floor heating doesn't get too hot. However, this is not the case, it is in fact physically one pump which pumps water through both circuits directly. It is called a LT/HT zone configuration by Intergas. Here is how it works: there are two thermostats, one downstairs and one upstairs. If the thermostat downstairs is asking for heat, the boiler will pump lukewarm water through the whole system, upstairs and downstairs. If the thermostat upstairs is asking for heat, the boiler will shutdown the system downstairs and pump hot water through the radiators upstairs. To do this, there is a electric valve in front of the low temperature circuit downstairs. If both thermostats ask for heat, the system will alternate between the two modes in 7 minute cycli. The idea of this system is that the boiler almost only needs to produce lukewarm water.

In practise, this system works well, and because of the good isolation of new homes, I hardly every change the temperature. Upstairs, the thermostat is set to "cold" (to ensure it never goes into high temperature mode), downstairs it is set to comfortable day and night.
I do have some smart radiator valves (thermostats) on a few radiators, but most radiators are currently permanently open.

However, I like some insight in the current usage and behaviour, some more control, and preferably feed the system with the outside temperature too. To give an example of the additional control: I want to be able to either shut down a specific radiator when that room is not in use, or want to demand for some more heat if I want to heat up a specific room. For that later, I need to add some logic (set the upper level thermostat with OT interface temporary to higher temperature till that room is heated, then set it to lower temperature again). In addition, there is a electric floor heating in the bathroom, so it becomes clear that I need to program some logic into a central controller.

Since I don't know of any "smart" off-the-shelf thermostat solutions that handle my situation, I thought I'm better off integrating these components myself.

For the central controller, I probably will have some work to do. I have a Homey, so my guess is to use that for the logic (good News: there are apps to control the radiator valves, the electrical heating and there is an app for the OTGF webserver, and some heating apps too).

My question: what do I need to buy to get this to work? I guess two OpenTherm Gateways for starters. Now, I'm a bit unclear about the best way to let this communicate with the controller (Homey or otherwise). Ideally, I like both Gateways to connect to the network using a single Ethernet cable.

Since the OTGW PCB features a RJ232 connector, my initial thought was to look for a Raspberry Pi with two serial interfaces (running two two instance of the OpenTherm Monitor software, listening on different TCP ports).

I haven't found such Rasberry Pi but I understand that there are also versions of the OTGW with USB ports or wifi or LAN. There is little information on that on otgw.tclcode.com, so I assume those are add-ons by 3rd party manufacturers.

Any advice for a good choice would be very much appreciated.

My preference would be to buy a pre-soldered version, as well as matching housing (I can cut or drill a bit, but don't have a 3D printer yet). Last (perhaps stupid) question: I'm of the opinion that open source and payment are not mutually exclusive. Is there an easy way to send a few euro commission to Schelte? Or select a shop where he benefits a bit?
hvxl
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Re: Boiler with dual OpenTherm interface: recommended use?

Post by hvxl »

I designed the OTGW with a serial interface because that was the easiest and I have an 8-port serial terminal server in the same cabinet where the OTGW was going to be located. To connect the device to a Raspberry Pi, you can just use a USB-Serial converter. These can be bought for a few Euro. In your case you'll need 2 (or one with 2 RS232 ports, but those are usually more expensive than 2 single ones).

It is true that the nodo shop offers versions of the OTGW with a USB or WiFi interface. But those are really just the original serial OTGW, with a serial to USB converter or serial to WiFi converter added on top.

Recently someone else also offered to make a donation to the project. While this is not necessary, the gesture is greatly appreciated. So I added a paypal link to the bottom of the main page of the web site.
Schelte
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