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Thread: Heating Partial Load

  1. #41
    Automated Home Ninja
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    Quote Originally Posted by bruce_miranda View Post
    Just make sure you don't have a Zone Valve on the CH that shuts off before even the first radiator. That's when the bypass is really needed.
    It's a combi, so there should be no motorised valves as the system isn't zoned as far as i'm aware.

  2. #42
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    I have a Vaillant ecotech 843 IQ with a EVohome system. The problem with the Partial Load D.000 set to auto is that when one or two rads call for heat it will often throttle the CH output so low that the CH water temp is only showing 40C for 30 mins or so - so no rapid heating of a room as required. I have set Partial Load to 24kW which stops this happening. D018 pump mode can also be set to Comfort which keeps the pump running all the time there is a heating demand. Finally I have reduced the anti-cycling time to allow the Evohome setting to dominate.
    It does seem that all these eco controls are not suitable when the boiler is controlled by a simple on/off demand switch especially in old houses when individual rooms will have very different heating requirements

  3. #43
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    This is where OT should, in theory, really help. The ability to vary the Target flow temperature based on Heat Demand is what is needed.

  4. #44
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    Quote Originally Posted by rarrarrar View Post
    I have a Vaillant ecotech 843 IQ with a EVohome system. The problem with the Partial Load D.000 set to auto is that when one or two rads call for heat it will often throttle the CH output so low that the CH water temp is only showing 40C for 30 mins or so - so no rapid heating of a room as required. I have set Partial Load to 24kW which stops this happening. D018 pump mode can also be set to Comfort which keeps the pump running all the time there is a heating demand. Finally I have reduced the anti-cycling time to allow the Evohome setting to dominate.
    It does seem that all these eco controls are not suitable when the boiler is controlled by a simple on/off demand switch especially in old houses when individual rooms will have very different heating requirements
    This is almost exactly what I have done. I've set heating partial load to a little more than the maximum of all my radiators open at once, D.018 to comfort, D.014 to 100% (thanks @mtmcgavock - this made a big difference, along with opening all the lock shields to full) and anti-cycle time to 15m, so at a 70 degree target flow the anti-cycle time is 2.5m.

    What's your anti-cycle time set to?

  5. #45
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    Quote Originally Posted by rs1987 View Post
    This is almost exactly what I have done. I've set heating partial load to a little more than the maximum of all my radiators open at once, D.018 to comfort, D.014 to 100% (thanks @mtmcgavock - this made a big difference, along with opening all the lock shields to full) and anti-cycle time to 15m, so at a 70 degree target flow the anti-cycle time is 2.5m.

    What's your anti-cycle time set to?
    Boiler max anti-cycle time D.002 is set to 6 mins ( default is 20)
    EvoHome has min burn time of 3 mins and 6 cycles per hour.
    Although short cycle times are in-efficient , in a large Victorian house with not great insulation and individual room controls waiting 20 mins before heat comes through is not acceptable.

    It would be nice for Evohome to be able to adjust boiler CH temp based on zone demand %.

    If I made the boiler choice again I would not have gone for the Green IQ model but one with less sophisticated control, however at the time it was suggested that new Regs could not be met with a more basic boiler and an on/off control from the EvoHome .

  6. #46
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    Evohome already offers OpenTherm - which does indeed adjust the CH temp based on the zone demand %.

  7. #47
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    Quote Originally Posted by bruce_miranda View Post
    Evohome already offers OpenTherm - which does indeed adjust the CH temp based on the zone demand %.
    Not in UK and some forum posts have suggested issues.

  8. #48
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    Quote Originally Posted by rarrarrar View Post
    Boiler max anti-cycle time D.002 is set to 6 mins ( default is 20)
    EvoHome has min burn time of 3 mins and 6 cycles per hour.
    Although short cycle times are in-efficient , in a large Victorian house with not great insulation and individual room controls waiting 20 mins before heat comes through is not acceptable.
    I put my minimum burn time up to 5 minutes and the anti-cycle timer on 10 mins. The shorter cycle was just not working as effectively. I'd rather have a 0.5 degree overshoot than a 0.5 degree undershoot.

  9. #49
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    Quote Originally Posted by rarrarrar View Post
    Not in UK and some forum posts have suggested issues.
    Issues Like?

  10. #50
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    has anyone figured out evohome opentherm r8810 with a worcester boiler yet? tried the nefit converter couldn't control the boiler firing so went back to bdr91. I too was trying to improve cycling/efficiency I've since changed some settings and seeing how it goes.

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