Central heating return temperature on opentherm

[Bart]

Opentherm supports return temperature, but is this parameter used by evohome for control setpoint (to keep the boiler in condensing mode as much as possible)?
My boiler does not support the measurement of return water temperature, and I wonder if that affects the way that evohome manages heat demand.

[Richard]

Lots of boilers don't support a return water temperature Control ID...

As long as the flow temp is maintained under 55-60 degrees the boiler will naturally condense...

A boiler and associated heating system designed for a Delta T of 20 Deg C running at 70 degrees flow temp would mean return temperatures that would cause the boilers flue gasses to condense...

[Bart]

Taking in to consideration that return temperature is the only factor that determines if a boiler makes use of energy from condensation or not, and if Evohome does not use this info (if available) in the heat demand calculations, I find it debatable whether Evohome should be averted as a system that uses the boiler as much as possible in the condensation range. One can only claim that about a whole heating system, including adequately sized radiators and flow, maximum output temperature, no automatic bypass valve should be present, etc.
As it seems strictly from the Evohome perspective, making use of condensation energy is only a secondary effect, by no means deliberate actions are taken by the controller to get to / remain in condensation mode.

I've seen discussions about delta T, I've seen 12 degrees Celsius mentioned as a rule of thumb for calibration in older systems, the 20 you say would be great - and feasible when designing a new system, but not always possible on older systems that facing upgrades to the boiler and control system.

[Richard]

Taking in to consideration that return temperature is the only factor that determines if a boiler makes use of energy from condensation or not, and if Evohome does not use this info (if available) in the heat demand calculations, I find it debatable whether Evohome should be averted as a system that uses the boiler as much as possible in the condensation range. One can only claim that about a whole heating system, including adequately sized radiators and flow, maximum output temperature, no automatic bypass valve should be present, etc.
As it seems strictly from the Evohome perspective, making use of condensation energy is only a secondary effect, by no means deliberate actions are taken by the controller to get to / remain in condensation mode.

I've seen discussions about delta T, I've seen 12 degrees Celsius mentioned as a rule of thumb for calibration in older systems, the 20 you say would be great - and feasible when designing a new system, but not always possible on older systems that facing upgrades to the boiler and control system.

I don't think its evohome that states that it uses the boiler in condensing mode as much as possible, I think it was a Honeywell statement about OpenTherm in general. evohome is very much a system that concentrates on 'comfort' rather than 'efficiency' and will achieve comfort however it sees fit. The side effect of multiple sensors around the house is efficiency.

As for flow and return water temperature differences (delta T), all new condensing boilers (since early 2000's) are designed for 20 deg C. You must bear in mind that older boilers will be on/off boilers and not modulating condensing boilers so can run at Delta T 11 deg C. All new boilers should be installed to run at Delta T 20 deg C and if this means radiator upgrades, then this should be the case to ensure optimum efficiency.