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Need some help optimizing fuel consumption of my Vitodens 100 boiler
I have a Vitodens 100 boiler with a low loss header and VT2218 delta-T circulator feeding old gravity piping with cast iron radiators. My problem is that installer used default settings for boiler outdoor reset heating curve and 20 F delta-T setpoint for circulator. The system gets hot very fast (180 F boiler water @ 14 F outdoor temperature).
In an effort to improve fuel efficiency, I decided to take a less aggressive approach and try a heating curve making 150 F boiler water @ 4 F outdoor temperature (average winter minimum temperature is 4 F in my area). This leaves some room to handle colder weather down to -26 F @ 180 F boiler water (extreme minimum winter temperature for my area is -40 F)
The other trick is to get the circulator pumping faster with the winter weather. I intially was hoping to use a delta-T setpoint of 35 F on the circulator to minimise boiler return water temperature, but I'm afraid that it would slow the pump down too much and for too long and won't give me the heat flow I need to heat the house. I took a cue from the measured delta-T always settling down to 15 F by the end of a heating cycle. So far, in warm weather, the delta-T setting of 15 F on the ciculator gives a very smooth operation with the circulator in control of delta-T at all times. I tried running the circulator with a delta-T setting of 20 F, but the boiler and circulator started making wild swings during the early stages of the heating cycle and during the later part of the heating cycle lost control as the delta-T dropped below the setpoint and the circulator was already operating at minimum speed.
Hope this makes some sense, as hydronics is not my field of expertise.