Vitodens Operation

Mike T., Swampeast MO

Here are 12 days including the coldest weather we have had in a few years. Maximum sustained input of the boiler was about 70 mbh with 91 mbh possible.

Outside Temp is SOLAR INFLUENCED!

"Target Temp" is NOT measured--it is based on the reset curve of the boiler. The temperature I measure (Supply Temp) continues to be significantly less than the "boiler temp" reported by the Vitodens. I'm measuring the surface temp of 1" black iron about 3' from the boiler.

The burner has fired nearly continually during the period--shutting down for short times during the "heat" of the day on the 18th, 21st and 29th. Viessmann literature states that the boiler will conduct some sort of internal test after 24 hours of continual operation. It almost appears to be doing this right around 1:47 p.m. each day. Kind of interesting that such tends to correspond quite closely to the period of greatest solar influence...

The very rapid dips you see in the supply and return temps are when TRV settings were changed. I conducted numerous response tests during the period--they involved greatly varying numbers of TRVs and radiator EDR. Note how rapidly the original supply curve is resumed and that there is no "boost" in the traditional sense--just a greater amount of heat being supplied to meet the varying demand.

The remarkable consistency of the return temperature despite wildly varying outside temps and changing TRV settings is a big surprising to me. I had expected the return temperature to rise more significantly during cold weather with delta-t remaining more steady. Instead, delta-t appears to be a good indicator of the load on the system. Again the "target temperature" on the graph will be VERY close to the "boiler temperature" reported by the Vitodens. If I measure delta-t as the difference between the "target temperature" and return temperature, Delta-t was as high as 46° with about 25° the minimum.

As far as I can tell, energy consumption dropped by about 45% during this period (as compared to the old cast iron W/M). That compares to a reduction of about 53% is more moderate weather. The response tests however are neither cheap nor particularly efficient. During this period last year I was exceptionally frugal (or is that stingy) with the heat. My ground floor continues to be under renovation with the real living quarters in the attic. Due to a fire in my store and lack of both time and money, there was no work done on the ground floor last winter with the TRVs kept at the lowest possible setting. Also, only my office on the 2nd floor was in constant use. This year the master suite is in use by a student and work is progressing on the ground floor. Am keeping the ground floor at my "work perfect" temp of about 58°-62°.

For the most, the only way I can tell that the boiler has changed is because of the decrease in fuel. Setback recovery remains extremely strong for a hydronic system and the radiant baths perform almost identically. Daily temperature variance in occupied rooms remains about 4°--a bit higher on sunny days with the shades open and with extremely cold nights. This variance seems a touch greater than in years past, but I have no comparable period with data logs to compare. In unoccupied and undisturbed rooms, temp variance is very, very low--about 1½°.

Constantin

Congratulations...

... not only for sharing your observations, but also for enlightening the rest of us with respect to the capabilities of the Vitodens. While a side-by-side comparison test is practically impossible, your work is about as close at it gets.

BTW, are you comparing the gas consumption on a per degree-day basis? I presume you are... thanks again.

Mark Eatherton1

Velly Intellesting...

So, what in essence you're saying is the same thing that all the people who've done conversions from a typical 80% boiler to this highly efficient condensing technology are saying. You $aved $ome $erious buckage.

Great Job.

ME

S Ebels

Supply vs Return

Interesting to see how the supply varies according to the O/D temp while the mean variation of the return is almost nil. I would have to assume the the variable speed circ is doing its job properly and seeking the best speed for optimum efficiency, as it's supposed to.

The Vitodens is way cool to put it mildly.

Mike T., Swampeast MO

Gas consumption

Degree days plus subtraction for DHW usage so accuracy takes a definite hit. ±5% should be fair.

Mike T., Swampeast MO

Here's the Solar Component Design

Happy New Years Viessmann. I believe this is the "simmer" adjustment...

The goal is to eliminate as much of the "pulse mode" as possible. Otherwise the solar is collected for DHW use.

The only space heating input required from the Vitodens is whether or not the unit is firing; the rest is handled by a separate control. It need only modulate a three-way valve directly with temperature differential.

Please critique.

Mike T., Swampeast MO

From the skanty operational description, I don't believe that the circulator is able to "seek the best speed for optimum efficiency". Instead, it is linked to outdoor temp--the colder it gets, the faster it turns.

Since it's a gravity conversion with all of that piping and water content, I suspected that the return temperature would become a "lead anchor"--how big of an anchor was a bit surprising.

The boiler is fully capable of introducing rapid and substantial changes in the return temperature--either by changing TRV setting or when it is not modulating.

It seems to be the modulating burner that's doing such a fantastic job. Even though the engineering is surely complex, the action seems pure simplicity. The combustion blower is the key because it regulates the flow of fuel to achieve the target. The boiler itself only seems to know two things regarding the flow of fuel: 1) "I'm at minimum" and 2) "I'm at maximum". Anything in between is a function of: 1) distance of actual boiler temperature from the target and 2) resistance to air flow in the flue. It's this deceptively simple link that allows an amazing tolerance to wind, icing and line voltage--everything self-adapts non-mechanically.

Mike T., Swampeast MO

Yep, that's what it boils down to. Being precocious, I just want to know "how" and "why".