Fuel Savings with New Vitodens

Mike T., Swampeast MO

Have enough data to make a reasonable estimate.

Standing iron system with 4 small radiant areas (baths). Thermostatic radiator valves, constant circulation and full outdoor reset. Only change was the boiler. Weil-McLain CGM-6 old; Viessmann Vitodens 6-24 new. Single circulator with both systems (B&G 100 old; the built-in Grundfoss new).

Used simple degree days as reported by Weather Underground and three years of gas billing statements. Did make an "average" subtraction (identical for both boilers) for the DHW. Neither system provided DHW.

For the bulk of the heating season from December through February:

W/M = .36 therms per degree day

Viessmann = .23 therms per degree day

Reduction = 38%

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For the "shoulder" months of November and March am having some difficulty. The old system was a true gas hog in those months and I usually used forced air electric. Even with the warm-weather shutdown set at 55°, as best as I can tell therms per degree day in those conditions increased to at least .43

The Vitodens is the opposite. It gets more efficient in the shoulder months. For November it reduced to about .21 therms per degree day. With manipulation of the reset shift via the "sun" and "moon" dials and automated switchover based on outdoor temp, have reduced that further to about .17 therms per degree day in March.

So, for the shoulder months fuel reduction is about 60%. Those months make up about 26% of the seasonal consumption, so:

(.60 * 26) + (.38 * 74) = 43.7% reduction over the entire season.

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With natural gas this year costing $1.1753 per therm, savings estimated at 306 therms or $359.64. Important to note that this winter here was somewhat warmer than the last two and a bit warmer than average.

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Since the distribution and basic control system were unchanged between the two boilers and already about as efficient as possible for this system, this should be a quite fair comparison of the boilers themselves. Had the Vitodens been installed in a "bang-bang" gravity conversion with a similar or even older boiler, I suspect that savings would have been more dramatic.

My original fuel reduction estimate (before the boiler was purchased) was 47%. Have calculated 43.7% actual. I did run a number of response tests with the new boiler--some quite large when the outside temp was falling rapidly. Did keep the 2nd floor at very similar indoor conditions, but kept the ground floor about 3° - 4° warmer.

Mike T., Swampeast MO

\"Payback\"

Payback is both the most important factor to many people yet still the most difficult to calculate. "Your mileage may vary..."

Replacement (as opposed to new construction) only complicates matters.

I would guess that many wait until their heating appliance is at or near death--and then make a snap decision on replacement. Unforeseen and unplanned expenses often result in the least expensive replacement.

In my case I chose to save a bit and replace a 30 year-old boiler before it died. I did choose the most expensive residential boiler on the market. BUT, that expense is relative. For this system, it was also the simplest--by far--to install. Even without the TRVs, a Vitodens installation on a gravity conversion system is not particularly difficult.

With labor costs at or even below any other replacement, the payback becomes quite rapid. Four years or less in my case.

Again, your mileage may vary, but here are my most sincere recommendations:

1) If you're a homeowner like me with standing iron radiators that you want to keep, ask for the Viessmann Vitodens BY NAME! If you want to maximize your comfort and savings at the expense of longer payback due to increased material cost, install thermostatic radiator valves (TRVs) at the same time.

2) If you're a contractor who works on these systems, recommend the Vitodens (or your personal condensing/modulating boiler preference) and TRVs to your customers. During service of older boilers, suggest that they save a bit to avoid having to make a hasty decision.

joel_25

hey mike

You are my hero can you and Constantine be my customer , please... we'd be gratefull if you could post all those cool charts and data you've been collecting all at once , thank you.

Constantin

Thanks Joel!

...I think I'll take that as a compliment... ;-)

I too hope to start logging more info as time goes by to see how well the solar system fulfills our DWH needs. Attached is a small pic of our Vitosol overhang, possibly a creative awning for those of us who try to keep the summer sun out of our homes.

As ME points out though, don't expect these babies to survive indefinitely in hail-prone areas or near golf courses. Radiantly yours, Constantin

Mike T., Swampeast MO

Here's the Program and Data

Hope this works.

NOTE: This is written for 1600 x 1200 screen resolution. It will run with lower resolution, but items will be clipped at both bottom and right and there are no scroll bars.

TO LOAD:

1) Create a directory (folder) in C: drive named: C:Temp Data Program (note three words)

2) Right click on each attachment, and select "Save Target As". Navigate to the Temp Data Program directory and you will have to manually enter the file name--if you don't they'll be renamed "attachment". Upper/lower case shouldn't matter, but the original names are:

Vitodens Tracking.exe

RESET.SEQ

BigV.ico

PC_WETTER.EXP

BigV.ico is the icon file for the program. Not needed, but if you like you can associate it with Vitodens Tracking.exe or use as you like.

Vitodens Tracking.exe created with Visual Basic 6. It should run on most computers without problem. If I have the time, will modify it later for lower screen resolution.

Ignore condensate data. The rainfall sensor may be overloaded. I might not be properly interpreting the data. The pigden English calibration instructions that supposedly allow me to associate a volume of water with inches of rain may be bad. Remember that the outside temp sensor is on the South side of the house, so it's solar influenced. The Supply Target relies on outdoor temp, so it takes a big dip on sunny days.

Excepting very short periods, the reset curve has remained the same throughout the season. The automatic sun/moon switching was added in late February. You'll see the supply target drop to 32° in warmer weather after that time BUT the target does not reflect the lowered setting of the moon dial--only shutdown. Earlier in the season, the target will drop off, but shutown did not occur. If it annoys you, use the Set menu to adjust the "alternate origin" to 68°.

Mike T., Swampeast MO

Those collectors have a curious beauty. Vitodens took my "play" money and have a very large kitchen and solid cherry paneled library to build in the next two years.

bob_34

fuel savings with new vitodens

mike, did you have the outdoor reset on the cgm-6? sounds like you did. if so i have almost exactly the same setup -about 13 years old, cgm7 and argo outdoor reset. all baseboard and 6 zones. i have a basement office loop of 6000 btus that tends to call for heat when the rest of the house is being warmed by solar gain in these shoulder months. when this below ground loop calls the 210,000 btus fire up to satisfy the 6000 btu demand. i like the reliability and simplicity of the cgm but the sharp rise in natural gas cost in the last 18 months [about 65% here in new hampshire]. and now your analysis of more savings than i had probably imagined may be driving me over the edge to something that will sip gas when one small zone calls. probably an ultra with an uninterrupted power supply. thanks for the analysis.

Mike T., Swampeast MO

Yes, used full reset with the CGM. SUPPLY only hit 140° at outdoor design of 8°, so the return never even came close to 140°. Before reset was added temps were even lower--particularly return. Original draft hood still in good shape--no rust or rot, just dirt. Heat exchanger only has surface rust. I suspect the oversizing of the boiler combined with the high volume of the system to keep condensate damage away. Had I replaced with a properly sized conventional boiler where the mfgrs. have eaked out the last drop of efficiency, believe I would have had to be concerned with condensation.

Really hard to compare between an old gravity system with iron radiators, TRVs and a baseboard system with six zones.

That said, homeowners and contractors here alike report high comfort and savings with a condensing AND modulating boiler on baseboard systems. A well-sized modulating boiler should be able to handle your basement much better than one that always fires at the full rate.

Since your boiler is relatively new and probably has many more years of life, your payback period will be greatly extended--even with increasing gas prices. Very difficult to even estimate since there are so many unknowns.

I certainly wouldn't replace if you finance the job with a loan unless you are quite certain it can be paid off in a year or less.

From my understanding, an Ultra should be a very good choice for your system. Just make certain that the water is checked periodically for any problems that might accelerate corrosion of an aluminum heat exchanger.

S Ebels

If I'm reading between the lines correctly...........

It would appear that the large percentage of the increase in efficiency is coming from the modulation. More-so than the outright difference in efficiency. If it were just a raw efficency increase the savings would be similar throughout the entire heating season. Being that the most substantial increases were noted in the shoulder seasons I have to think the modualtion is playing the larger part.

Does that fit with you Mike?

Mike T., Swampeast MO

Steve

I think the higher efficiency in the shoulder seasons is more related to low return temp and the fact that I've turned my home into a "Euro Cave" [thanks for the term ME] when it's warmer than 40 outside. 40 degrees is the point where the burner STOPS modulating....

Mike T., Swampeast MO

Just had a storm of marble sized hail from the South.

Mark Eatherton1

Marble sized is OK...

its the GOLF BALL size and larger that cause havoc with ejaculated tube correctors (Japanes style) :-)

ME

Mike T., Swampeast MO

Sorry for the short and incomplete reply Steve. Am working on a housed string staircase with "dancing" treads at the bottom quarter-turn. Angled mortises are tedious and almost no margin for error.

The one thing I can say confidently is that the AFUE numbers are nonsense when it comes to comparing the two boilers.

As a class, condensing boilers seem very efficient at delivering the energy from the fuel into the system and keeping it out of the flue. The lower the temps (supply and return involved) the more heat they seem to extract.

The role of modulation in the efficiency equation seems to be the ability to keep temperatures as low as possible while still satisfying the structure. Once you have smooth modulation, I've found that the boiler modulates smoothly regardless of the reset curve.

To utterly maximize efficiency in an "ideal" system you really want the temps as low as possible--the modulation makes this easy. This allows you maximize the amount of condensation.

Unfortunately, my system is NOT ideal. The radiation is quite imbalanced (inherited and only made worse with insulation/weatherization). I also have those "super-simple" radiant floors.

Was told by Viessmann that in the U.S. the boiler is frequently set for a MUCH higher curve than is truly needed. I know this is true for mine. After measuring the actual temps of radiators and returns throughout the house, I set the curve WAY down. The house still heated to setpoint, but the radiant floors suffered.

With the curve down to the minimum I felt something very unusual in the house. The "coziness" was gone and it was virtually impossible to raise space temp by turning up TRVs. That's when Mark Etherton said, "welcome to the Euro-cave".

The data-logging indoor temp sensors duitifully showed no real change in indoor air temp, but things just weren't as comfortable. My guess is that the reduced comfort level is greatly related to mean radiant temperature. There are lots of large windows in the house. They're about as good as you can get with windows from 1903 via storms and good weatherstripping, but far from the "super windows" now available. I very much suspect that the interior glass surface had dropped in temperature and was sucking more radiant energy from my exposed skin.

The efficiency difference between November and the rest of the season wasn't much--after all, it was operating at the same reset curve. That slight difference would [seem] related almost solely to lower system temperatures.

Don't forget that in mild weather the boiler is NOT modulating (in fact it frequently heats the place with small heat injections at full fire). When it does modulate down to low fire for an extended period, it is still NOT true modulation. The supply temperature rises and falls significantly during those periods--just like it does with any digitally controlled burner. In those conditions the Vitodens becomes either a staged low- or high- fire boiler--NOT modulating. The staging helps with efficiency, but I just can't bring myself to call that type of operation "modulating".

So, in this system I'm really not taking full advantage of the efficiency you can get through modulation--particularly in colder weather. I honestly suspect another 10% (or even greater) efficiency increase if I forgot about my radiant floors, accepted slow response when a TRV is turned up and somewhat reduced comfort. Could solve the radiant floor problem with extensive and expensive piping changes, but don't believe it worth the expense. Since I do and always will keep unused spaces set back deeply, the rapid response is VERY nice to have. NO WAY I'm replacing my windows, so for the same comfort level I'd have to increase the TRV setting. Nothing is more uncomfortable to me than sweating while wearing a heavy sweater....

What I did find though is that during weather when the boiler can't truly modulate anyway, that the "Euro-cave" isn't too bad as long as there aren't multiple days of very cloudy weather. In those conditions, I suspect that I'm getting the maximum efficiency possible for this boiler in this system. When the boiler is "pulsing" the return temperature stays perfectly steady and hovers near 68°. In November in the same outdoor conditions, the return temp oscillated VERY slightly near 80°.

Mike T., Swampeast MO

Has anyone tried the program?

If so, please let me know if it worked. This is the first VB program I tried to distribute and not sure if it takes a run-time module or similar.

Am curious how others analyze the data. Considering the "normal" chaos of heating in the real world, it sure seems refined and rather straight-forward to me.

Will keep collecting and reporting this data for years. WOULD REALLY APPRECIATE SUGGESTIONS ON WHAT YOU WANT TO SEE.

Have thought of moving the supply temp sensor INSIDE the boiler as close to the HX outlet as possible. Is that a good idea? Am currently measuring the surface temp of black iron about 3' from the boiler.