I’m looking at adding weather compensation to my Evohome Intergas OpenTherm setup by customising the OTGW firmware.
The good thing is that the OTGW can read the Outside temperature from the external sensor connected to the boiler.
The R8810 OpenTherm bridge calculates the control setpoint from percentage demand based on the Max CH water setpoint.
The latter defaults to 90C with Intergas even if Tmax is manually set lower via the boiler temperature display. The boiler will clamp the maximum to the boiler setting though e.g. 60C.
It is possible to set Tmax lower from the OTGW. Immediately the control setpoint is seen to reduce proportionally.
I’m looking for a recommendation on the best algorithm for weather compensation.
1. Should I reduce the Max CH water setpoint based on the outside temperature according to a heating line.
2. Or should I clamp the control setpoint temperature, based on a maximum calculated from the outside temperature, leaving the Max CH water setpoint at 90C?
The difference will be that for the latter a % demand will be mapped to a consistent temperature as long as that temperature is below a weather compensated maximum.
But for the former the % demand will map to a different temperature based on the outside temperature, lowering as the outside temperature increases?
The good thing is that the OTGW can read the Outside temperature from the external sensor connected to the boiler.
The R8810 OpenTherm bridge calculates the control setpoint from percentage demand based on the Max CH water setpoint.
The latter defaults to 90C with Intergas even if Tmax is manually set lower via the boiler temperature display. The boiler will clamp the maximum to the boiler setting though e.g. 60C.
It is possible to set Tmax lower from the OTGW. Immediately the control setpoint is seen to reduce proportionally.
I’m looking for a recommendation on the best algorithm for weather compensation.
1. Should I reduce the Max CH water setpoint based on the outside temperature according to a heating line.
2. Or should I clamp the control setpoint temperature, based on a maximum calculated from the outside temperature, leaving the Max CH water setpoint at 90C?
The difference will be that for the latter a % demand will be mapped to a consistent temperature as long as that temperature is below a weather compensated maximum.
But for the former the % demand will map to a different temperature based on the outside temperature, lowering as the outside temperature increases?
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