on/off to Opentherm

This Forum is about the Opentherm gateway (OTG) from Schelte

Moderator: hvxl

on/off to Opentherm

Postby stijn.k » Sat May 11, 2019 12:42 pm

Hey
I have a question. my home automation system only supports on/off boilers. but we now have a new heat pump that does not work with on/off Can I switch the on/off signal to Opentherm with a gateway?
I would love to hear more about this.
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Re: on/off to Opentherm

Postby marcelr » Sat May 11, 2019 3:17 pm

Highly unlikely, it's a totally different protocol. You can emulate on/off with an OpenTherm device (e.g., Google Nest ...), but the other way around is not possible AFAIK.
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Re: on/off to Opentherm

Postby hvxl » Tue May 14, 2019 12:51 pm

The OTGW can do a very simplistic conversion from on/off to opentherm. If the contacts on thermostat interface are shorted, the OTGW will send opentherm messages to the boiler asking for a water temperature of 80 degrees at maximum 100% relative modulation. While this may somewhat work for normal boilers, I have no idea what will happen with a heat pump. I have heard rumours that some heat pumps actually operate based on room temperature and setpoint, rather than the control setpoint. Since the OTGW does not have information on room temperature or setpoint when no opentherm thermostat is connected, it does not send those messages.
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