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Thread: Evohome + HGI80 & Domoticz users - zones calling for heat functionality?

  1. #111
    Automated Home Guru
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    No, please don't shut up . The more users that ask about a feature the more likely it is to rise to the top of my to-do list. To make it enjoyable, I have to find something to finish every few weeks. So, I'm often switching tasks when I hit a roadblock.

    The differential gives you the lower temperature (setpoint minus differential) which triggers the DHW to re-heat. There's also the overrun setting in the controller menu which keeps the DHW valve open for the specified time after the boiler demand has stopped to extract further heat (I'm not 100% sure that this value is sent in the 10A0 message though).

  2. #112
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    That makes sense. I'd call that hysteresis, or trigger level, or something.

    Not sure what benefit there is to sending in the message though? Perhaps the OT Gateway uses it to blend DHW and CH demand into a final heat demand from the boiler?

  3. #113
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    The differential is just another name for hysteresis yes.

    I think you're confusing the hot water sensor and OpenTherm bridge - the hot water differential is sent in the communications between controller and CS92A. The CS92A is informed of the user set hot water set point and differential so that it's battery saving algorithm can make better decisions about when to transmit temperature updates.

    Below setpoint-differential updates are very infrequent (once an hour I think) unless there is a change of several degrees. In the differential range updates are much more frequent (about one per degree rise) and when the set point is crossed an update is always sent immediately to avoid heating past the set point.

    To do this the controller has to be able to communicate to the CS92A what the set point and differential actually are.
    Last edited by DBMandrake; 9th February 2017 at 06:53 PM.

  4. #114
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    Quote Originally Posted by DBMandrake View Post
    The differential is just another name for hysteresis yes.
    Maybe. I was just saying what I'd call it!

    Quote Originally Posted by DBMandrake View Post
    I think you're confusing the hot water sensor and OpenTherm bridge.
    Not at all. I just hadn't considered that the controller might broadcast that information at all, let alone for the benefit of the temperature sensor! Do you have an evidence that the CS92A does what you've described? That would be pretty clever if so.

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