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Thread: Boiler with separate HW and CH max and OpenTherm

  1. #61
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    I dropped Honeywell a message via their evohome web message service to ask about adding functionality to control the max CH temp. Though the lady seemed pretty knowledgeable, she said she would pass it on to the technical people.

    Might also be worth everyone else dropping them a line if they think it would be a useful upgrade to be able to set max temps within evohome for OT demand?

    I also suggested being able to calibrate the max heat demand dependent on difference in zone temps ie 10 deg colder- max 70, 5 deg colder say 60, 3 deg colder say 55 etc

  2. #62
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    Quote Originally Posted by fergie View Post
    I dropped Honeywell a message via their evohome web message service to ask about adding functionality to control the max CH temp. Though the lady seemed pretty knowledgeable, she said she would pass it on to the technical people.

    Might also be worth everyone else dropping them a line if they think it would be a useful upgrade to be able to set max temps within evohome for OT demand?

    I also suggested being able to calibrate the max heat demand dependent on difference in zone temps ie 10 deg colder- max 70, 5 deg colder say 60, 3 deg colder say 55 etc
    There is some logic to these requests; however, unless people are constant zone temperature fiddlers, I do not see a particularly large energy saving. This morning, with an OAT close to 0C, my usage in the first hour was 0.7CM3s or about 8kWhs. I now just let Evohome do its own thing and consumption over the past hour was only 0.3CM3s or 3kWhs. Yesterday, again with a cold start, my total usage was 46kWhs. My settings are 3 zones at 20C, with the other 9 zones at a constant 15C. I appreciate that no two houses are the same; however, I have learnt that using the Economy mode during the day actually costs me more thanks to Honeywell's heating logic. My boiler is currently operating with an OT demand of 29% ( highest zone 26%) with a Flow Temp of 52C and return of 42C. Heating is optimum start at 07:30 and Optimum Stop at 22:30.

    Screen Shot 2018-01-31 at 12.56.32.jpg

    The spike at 9am was when my wife had a bath and the the system switched to HW re-heat.

  3. #63
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    How are you monitoring? Iíd like to be able to take graphs like that

    My house is very efficient, but different size rooms heat at different speeds and different rooms are used at different times on different days. A lot of the time the boiler is showing me say 70deg our temp and 69deg return - a complete waste. Iíd be happy to have zones heat slower if it is more efficient. What I donít want is a difference of more than 1 deg that makes the boiler run at full pelt.

  4. #64
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    Quote Originally Posted by fergie View Post
    How are you monitoring? I’d like to be able to take graphs like that

    My house is very efficient, but different size rooms heat at different speeds and different rooms are used at different times on different days. A lot of the time the boiler is showing me say 70deg our temp and 69deg return - a complete waste. I’d be happy to have zones heat slower if it is more efficient. What I don’t want is a difference of more than 1 deg that makes the boiler run at full pelt.
    I bought a NorthQ Gas Optical Spot Monitor off Fleabay for £30. Cheaper than Loop Energy as it is a standalone product. It's 100% accurate to 3 decimal places as it is just recording complete revolutions of the last digit.

  5. #65
    Automated Home Legend paulockenden's Avatar
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    I've been pondering this requirement for a separate max temp for CH and DHW when using OpenTherm.

    Although it sounds sensible to have them different, using the same flow temp for both is only the same as happens with a BDR91 controlled boiler, isn't it?

    P.

  6. #66
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    Quote Originally Posted by paulockenden View Post
    I've been pondering this requirement for a separate max temp for CH and DHW when using OpenTherm.

    Although it sounds sensible to have them different, using the same flow temp for both is only the same as happens with a BDR91 controlled boiler, isn't it?
    Yes, but that's out of necessity. It's the only option available with BDR control. That doesn't mean it's the best and only option. If better control can be achieved, but only if using OpenTherm, then why not do it?

  7. #67
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    Imo it is very straightforward to do. I actually thought OT told the boiler if it were CH or HW its heating, but sadly not.

    So if all OT is sending is a temperature command, it would be very easy for it to distinguish itís self betweeen CH and HT and therefore send a revised temp via OT to the boiler - rather than trying to demand 90 deg all the time!

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