Opentherm - calculating boiler control setpoint
Posted: Sun Dec 13, 2015 9:37 pm
Hi opentherm guru's
I am trying to construct a multi-zone heating system. Basic idea is that in the daytime the boiler would use the standard (Rehema iSense) thermostat in the the living room and in the night time use an alternative temperature sensor (MAX! wall thermostat) in the master bedroom. For those interested, hw consists of a RPI, OTGW with otmonitor and MAX! cube + wall thermostat and radiator valve controls. Using FHEM as domotica sw. Works great but just missing one thing, how to calculate the boiler temperature control setpoint when I am using the bedroom thermostat? Btw, the iSense does a great job in maintaining the room temperature when set to a constant setpoint.
I set the room temperature to a constant 21.5 oC and logged the boiler\thermostat data using FHEM and made a load of screenshots from the OTGW graphs. Trying to detect a pattern here. Easiest when nobody turns the hot water on
So far as I can see:
1: The (basic) boiler control setpoint calculated by the iSense varies (for a 21.5 oC room setpoint) between 40 and 45 oC. Seems to vary as a sinewave.
2: Periodically the control setpoint is increased to 90 oC for a short period of time. This seems to be triggered when the boiler water temperature falls to below the control setpoint by 5 oC.
3: This 90 oC boost ends when the boiler water temperature rises to about 10 oC above the control setpoint after a minimum boost time of +/- 4 mins.
Unfortunately the above observations do not always hold true. About 20% of the time the boosts seem to be triggered/stopped by something else. Turning on the hot water seems to have an impact, but this does not explain all the deviations. Also how does the thermostat calculate the basic bolier control setpoint.
Would be grateful if anybody could enlighten me further...
Thnx,
ModbusMan
I am trying to construct a multi-zone heating system. Basic idea is that in the daytime the boiler would use the standard (Rehema iSense) thermostat in the the living room and in the night time use an alternative temperature sensor (MAX! wall thermostat) in the master bedroom. For those interested, hw consists of a RPI, OTGW with otmonitor and MAX! cube + wall thermostat and radiator valve controls. Using FHEM as domotica sw. Works great but just missing one thing, how to calculate the boiler temperature control setpoint when I am using the bedroom thermostat? Btw, the iSense does a great job in maintaining the room temperature when set to a constant setpoint.
I set the room temperature to a constant 21.5 oC and logged the boiler\thermostat data using FHEM and made a load of screenshots from the OTGW graphs. Trying to detect a pattern here. Easiest when nobody turns the hot water on
So far as I can see:
1: The (basic) boiler control setpoint calculated by the iSense varies (for a 21.5 oC room setpoint) between 40 and 45 oC. Seems to vary as a sinewave.
2: Periodically the control setpoint is increased to 90 oC for a short period of time. This seems to be triggered when the boiler water temperature falls to below the control setpoint by 5 oC.
3: This 90 oC boost ends when the boiler water temperature rises to about 10 oC above the control setpoint after a minimum boost time of +/- 4 mins.
Unfortunately the above observations do not always hold true. About 20% of the time the boosts seem to be triggered/stopped by something else. Turning on the hot water seems to have an impact, but this does not explain all the deviations. Also how does the thermostat calculate the basic bolier control setpoint.
Would be grateful if anybody could enlighten me further...
Thnx,
ModbusMan