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Thread: Boiler with separate HW and CH max and OpenTherm

  1. #1
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    Default Boiler with separate HW and CH max and OpenTherm

    I have a Vaillant boiler which could use two different Max Flow temperatures depending on whether it was Hot Water (HW) or Central Heating (CH) demand. Problem is that you can use this feature only with Vaillant's own eBus controllers. That is not a route I want to go down especially since I have Evohome and OpenTherm controlling the boiler.

    Currently the way OpenTherm works with my boiler is that there is only a single Heating demand and OpenTherm sets the maximum flow temperature required based on the demand it receives from Evohome. My boiler allows me to limit the flow temperature but only the Central Heating max temperature knob is operational, the Hot Water temperature knob continues to stay redundant.

    Are there any boilers what work with OpenTherm where the max flow temperatures can be set separately and they work as such? I'm trying to see if it is even possible to have a lower max flow temperature when there is only CH demand and a higher max flow temperature when there is HW demand - while still using Opentherm.

    Are there any Vaillant boiler users that used to use an eBus controller before and how have connected an OT Bridge via the VR33? What happens then?

  2. #2
    Automated Home Ninja Dan_Robinson's Avatar
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    Intergas.

    Ideal Vogue

    I know which one I would have. And do have. Running in this configuration too.

  3. #3
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    So is your boiler able to use different max settings based on whether the demand is HW or CH and that demand is coming via the Evohome Opentherm bridge?

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    Automated Home Ninja Dan_Robinson's Avatar
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    Hot water demand comes from the hot water bdr. Evohome does not give a specific hot water command. Just a demand for 100%.

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    So are you using Opentherm and a BDR together to drive the boiler?

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    Automated Home Ninja Dan_Robinson's Avatar
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    Yep. OpenTherm is pretty pointless in hot water. Bdr activates the boiler for hot water. Boiler controls a diverter valve for the cylinder.

    Valve sits in Heating mode normally. OpenTherm bridge then regulates the heating setpoint.

  7. #7
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    OK excellent. So clearly your boiler has two switched inputs to allow this to happen. Which boiler is it BTW? I agree that OpenTherm is pretty pointless in HW, but my silly boiler can only switch between HW and CH mode via the eBUS as opposed to switched inputs. Hence I am having to think of another solution to achieve what you have managed.

  8. #8
    Automated Home Ninja Dan_Robinson's Avatar
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    You are discovering why the more discerning of us call them Faillant leakoTec.

    I have the Intergas Eco RF 24 installed as a system boiler on the D Plan.

    This is my go to boiler and configuration for any project with efficiency and performance on the spec sheet.

    On the 17th I start a job which has been named the "36DD Plan" as it is a brace of Intergas Eco RF 36 boilers with a 400 litre twin c coil cylinder. Each boiler has a coil on hot water priority.

    Because of the size of the house and Honeywell not letting mere mortals play with their posh toys, I have to use heatmiser controls and that will be linked with Control 4 etc. I will compensate the heating using the inTouch app (part of the boilers) which will give a very effective alternative.

    Here is a single boiler version doing 240 square metres of ufh across 4 floors and couple of radiators and towel rails:

    20160729_121434.jpg


    I was "summoned" to an M&E meeting at short notice, so knocked this up the night before to show them how it worked :

    Schematics.jpg
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

  9. #9
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    So are there any boilers that have the ability to have different HW and CH flow temperatures and where the OperTherm Gateway is able to tell the boiler what it is trying to heat? either HW or CH, or is the Opentherm gateway always assuming that all boilers are Heat Only and makes no difference between HW and CH, so just run everything at a higher flow temperature to satisfy both?

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    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by bruce_miranda View Post
    So are there any boilers that have the ability to have different HW and CH flow temperatures and where the OperTherm Gateway is able to tell the boiler what it is trying to heat? either HW or CH, or is the Opentherm gateway always assuming that all boilers are Heat Only and makes no difference between HW and CH, so just run everything at a higher flow temperature to satisfy both?
    the boiler will modulate to the flow temperature that the controller requests

    by Vaillant ecoTECplus with VR33 adapter and evohome with OT bridge does exactly this

    normal flow temp circa 45degC, when there is hot water cylinder demand the flow temperature is increased to the max set at the boiler, in my case 70degC

    the boiler simply responds to the new flow temp setpoint

    make sense?
    I work for Resideo, posts are personal and my own views.

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