Vitodens Cold Temp Boost
While I am a pretty decent technician, I am spread out over 4 or 6 areas from DDC to Power Generation and cannot focus on one area. Condensing boilers are not something we deal with so little background and almost zero experience. Viessmann has no local tech rep and national would not return calls.
The one that is giving me grief is the combination of 4 Vitodens 200s controlled by a Vistocontrol-S WB2 control panel. There is no associated domestic hot water system and it uses a low loss header. The system feeds a supply/return heating system that has heating coils in the main fan and the VAVs supplying offices.
Most of the time it works fine, but when we hit temperatures in the sub zero range, it simply does not supply enough heat to VAV box heating coils to maintain temperatures in office along the outside walls (no baseboard heat, just heating coil in the VAV box).
Someplace in the whole setup I would guess there is a toggle you can have it run to max temperature and not worry about the condensing portion.
I cannot find it. The best I came up with was to remove the supply line sensor and fake it out. That seems to work (short test) the reaction is to fire up to 3 boilers (in the test I saw) and they hit their limit at 175 or so, then shut-down and dropped to 145 or so and then started to fire again. I am not sure what it would do long term. Its very slow response and the concern is something gets unhappy and just shuts them all down completely.
What I would like is to be able to find a command or dry contact toggle that would simply make them run that way (we can tie it into the DDC system such that once the OAT drops to a point around 0 it triggers that).
Preferably through the Vitocontrol-S.
The max temp on the Vitodens 200 is 167 deg F. The way to do this is to adjust your heating curve on the Vitocontrol S. If it is working great at all but near design conditions, then maybe a reference point shift is the way to go. This can be accessed pretty easily, but not something that I am going to get into in an open forum.
Contact me through my profile and I will get you the info that you need to make the adjustment. There is also a way to activate an external call for heat which will make it ignore the Outdoor Reset Curve, but if you set it up correctly, you won't need to. Viessmann is our preferred boiler manufacturer for commercial boilers and we have taken the time to become C-Pro contractors with them. Also, let me know where your located.