Vitodens Operation

Mike T., Swampeast MO

Four days of solid modulation. Like the Energizer Bunny, it just goes and goes...

REMEMBER–Outside temps are <I>solar influenced</I>. New weatherproof temp sensor is on backorder.

"Target Temperature" is based on MY SIMPLE calculation of the reset curve in the Vitodens; 141° @ 8° outside with 0.8 shift. Temp I can measure continues to be significantly below the temperature reported by the boiler. "Boiler Temp" as reported when you first open the door is generally within a degree or so of my computed target (without solar influence).

Rapid dips in return temperature are from increasing TRV setting(s). First dip (about 7:00 a.m. on the 14th) is from one room; 2nd big dip (about 8:30 p.m. on the 14th) is from entire ground floor plus same room. Note how supply temp rapidly resumed the exact same curve, but return temp dropped (delta-t widened) until the TRVs were put back to their normal position a little bit after 4:00 p.m. on the 15th.

Turning up TRV(s) produces an immediate dip in return temp followed very closely by a dip in supply temp. Turning the TRV back down produces a rapid rise in return temp with little or no effect on supply temp.

The dips you see in the supply temp at midnight are from one minute of "reduced temperature mode" operation. (Took me a while to figure that out. Thought I had it set for continuous "normal temperature mode".)

The size of the dip seems to be a good indicator of the load on the system. Note that it is very sudden and quite deep during that big recovery response test on the 14th. Considering this is <B>only ONE MINUTE of reduced temperature mode operation</B>, and you can see the almost immediate drop in supply temperature it seems apparent that this puppy has TRUE modulation--not "stages" in ANY way...

Did a bit of tweaking of the curve and normal room temperature setting on the 14th--first time since boiler went into full operation on Nov 1.

Mike T., Swampeast MO

If You Wonder Why I'm Not Using Reduced Temp Mode

Three reasons:

1) Old boiler didn't have that option and I'm trying for the most comparable comparison.

2) My radiant floors really need constant circulation as their only control comes from the reset curve.

3) Still doubt if that little built-in circulator has sufficient flow ability to keep flow through the entire system if the supply temp drops significantly and all of the TRVs open wide.

Cliff Brady

Haven't hit steady state yet

but the my Pinnacle analog reset module has done well down to 15 degrees. Will see how the curve is at 5 degrees and maybe minus 5 Sunday. 46,000 BTUs is a lot of BTUs to get to a steady so far, but run times have been long and overshoot has all but disappeared and the cats are enjoying the uncovered radiators more.

Mike T., Swampeast MO

Outside temp down to 19° with strong North wind--about 15 mph with gusts up to 30.

Boiler consuming 55 cubic feet of gas per hour or about 61% of capacity.

Temp loss sheet shows loss of 55 mbh or about 80% of design loss. About 2/3 of house has about 7° of setback. Looks like my boiler sizing where I=B=R rating is right at adjusted design loss (85% of the HVAC-Calc value) will be fine. Strong winds tend to increase my loss by around 6%-7%. The adjusted loss is based on actual radiator temperatures with light wind.