Non-condensing vs. condensing boiler operation costs...

Skyline

Hot_water_fan said:

So your internal pump alone uses more electricity than my AC's blower! This is one reason I'm so intrigued by the Vitocrossal 300.

Yes, my Wiessmann boiler is not energy efficient when it comes to electricity and that's just the heating pump. The boiler also has a DHW pump and while I couldn't find the technical specs for this pump, it's probably just as "efficient" as the heat pump. This is based on the observed 235W, or 0.94KWh for the four hours period, electricity utilization. In all fairness, the burner runs ~80% capacity and some of the electricity utilization is related to the fan. In either case, this is more electricity utilization than four hours heating cycle with two zone pumps active, posted earlier (0.84KWh), when the burner runs ~20-30% capacity.

Look at the energy utilization, both NG and electricity for Wiessmann in the heart of the winter month (December, January, February) shows, that NG usage decreased 62 CCF, or ~15%. The chances are, that the 20 years old non-condensing TriAngle Tube boiler had a 70-75% efficiency by the end of its life. If that's correct, the Wiessmann boiler NG efficiency had been 85-90% efficiency for this period.

In the same period, the electricity utilization increased by 87 KWh, or ~5%, with overall boiler efficiency rating of 10%. If the TriAngle Tube boiler had a 70-75% efficiency, then the overall efficiency of the Viessmann boiler had been 80-85%, that resulted in ~$23 savings. That's the claimed "big saving" whoop-de-do for the winter month...

The AFUE only accounts for the NG utilization, it totally disregards electricity utilization. That's misleading in my view and can reduce AFUE rating by ~5-6%, just like with my current Viessmann boiler.

What makes you sure that the Vitocrossal 300 does not have similar, overall energy utilization envelop? Companies tend to reuse the same parts in new models with minor modifications. I could be wrong on that...

Disclaimer: While it is true, that "Numbers don't lie, people with numbers lie", the energy utilization numbers are on the utility bills. Do utility companies lie on the bill? Most, if not all, don't...

Hot_water_fan

Yes, my Wiessmann boiler is not energy efficient when it comes to electricity and that's just the heating pump.

I agree - a selling point of heating with water is the low distribution energy required if done right. I have a air system that can get 29k Btu/hr through the ducts using a maximum of 121 watts, for a distribution efficiency of 240 Btu/hr/w. An efficient circulator paired with an efficient system could easily be 10x more efficient.

What makes you sure that the Vitocrossal 300 does not have similar, overall energy utilization envelop? Companies tend to reuse the same parts in new models with minor modifications. I could be wrong on that...

The Vitocrossal differs from the Vitodens in a relevant way: it has basically no head loss through the boiler (it's like a buffer tank heated directly), while the Vitodens has a high head loss (13ft head at ~6gpm). Because of this, the Vitocrossal doesn't have a boiler pump. You could have used a single circulator instead of your three and attached an indirect. HTP also makes a similar high mass, low head loss boiler. There are other modcons that have low head loss without the high water mass (for space considerations).

The AFUE only accounts for the NG utilization, it totally disregards electricity utilization. That's misleading in my view and can reduce AFUE rating by ~5-6%, just like with my current Viessmann boiler

You're right! I think AFUE should include the blower and boiler pumps (maybe it already does). I don't think AFUE should include system pumps.

Look at the energy utilization, both NG and electricity for Wiessmann in the heart of the winter month (December, January, February) shows, that NG usage decreased 62 CCF, or ~15%. The chances are, that the 20 years old non-condensing TriAngle Tube boiler had a 70-75% efficiency by the end of its life. If that's correct, the Wiessmann boiler NG efficiency had been 85-90% efficiency for this period.

The Viessman efficiency numbers you give for these months are probably right - based on the curve you shared earlier, it probably wasn't condensing that much. Next winter, lowering water temps and flow rates (flow rates can be lowered significantly without impacting heat output that much) would be an interesting experiment. However, the Triangle Tube numbers are probably overstated because:
1. You have other natural gas appliances.
2. It's unclear if the DHW heating is condensing.

Subtracting out 1CCF/Day (I think this was July's usage) for other appliances and DHW (not included in AFUE right?), you saved ~20% during the coldest months on a CCF/Day basis, so the TT was less efficient. But we need to keep in mind the A in AFUE stands for Annual, so cherry picking the coldest months isn't what this measure is designed to do.

I'm most puzzled by the frost protection energy usage. Do you know how much time it spends in that mode? Did Viessman have any advice on that front?

Skyline

Hot_water_fan said:

The Viessman efficiency numbers you give for these months are probably right - based on the curve you shared earlier, it probably wasn't condensing that much. Next winter, lowering water temps and flow rates (flow rates can be lowered significantly without impacting heat output that much) would be an interesting experiment. However, the Triangle Tube numbers are probably overstated because:
1. You have other natural gas appliances.
2. It's unclear if the DHW heating is condensing.

Subtracting out 1CCF/Day (I think this was July's usage) for other appliances and DHW (not included in AFUE right?), you saved ~20% during the coldest months on a CCF/Day basis, so the TT was less efficient. But we need to keep in mind the A in AFUE stands for Annual, so cherry picking the coldest months isn't what this measure is designed to do.

Why would I need to substract anything? As the image states in the OP, in both seven month periods all NG and electricity utilizations included. The only thing changed in my system is the boiler and comparing the seven month period is based on the actual utility bills. While cherry picking three, or seven month for that matter may not seem fair to you, I respectfully disagree. Yes, the system has other NG appliances; they are the very same appliances as I had with the previous boiler. If I want to cherry pick... we used more NG during the 2019 - 2020 seven month period, due to the grand-kids taking long showers in my house 2 - 3 times a week and my wife baking Xmas cookies for a week prior to Xmas. Neither of them happened during the 2019 - 2020 seven month period and yes, I missed her cookies...

Oh, I will see the "Annual" results and probably you guys will as well. I fully intended to keep my spreadsheet going based on the utility bills for at least a year, possibly longer.

I'm most puzzled by the frost protection energy usage. Do you know how much time it spends in that mode? Did Viessman have any advice on that front?

From the Wiessmann manual:

Frost protection
■ The frost protection function will be started when the
outside temperature drops below approx. 34°F (1°C).
With the frost protection function, the heating circuit
pump will be switched ON and the boiler water is
maintained at a lower temperature of approx. 68°F
(20°C).
The DHW tank will be heated to approx. 68°F (20°C).
■ The frost protection function will be stopped when the
outside temperature rises above approx. 37°F (3°C)
(default settings).

During a cold snap, the boiler would run 3 - 4 days without shutting off, since the temperature did not reach 37°F (3°C). Disabling it would void the warranty if the boiler freezes up, as Wiessmann made it very clear to me.

The funny thing is, maybe not that funny, that the outdoor temperature sensor always shows 3 - 4°F (3°C) higher temperature than the actual outdoor temperature shown via my small weather station and/or the local weather station. In theory, the boiler could have frozen up, when it showed 34°F and the actual outdoor temperature was 30°F. This really didn't matter, since the boiler is indoors anyway, where the temperature never drops below 60 - 65°F.

This "feature" will be disabled prior to the next heating season...

Hot_water_fan

If I'm understanding it correctly, the boiler should be firing to heat the house nearly 100% of the time when the temperature is below 34 but you're saying it's not doing this and the frost protection is coming on as a result? Do you have an idea of what % of the time below 34 is spent in this mode? Even if you're oversized compared to minimum modulation, it shouldn't be that noticeable. The one cause I could think of would be the setbacks - maybe coming down in the evenings means the boiler spends a lot of time off.

Why would I need to substract anything? As the image states in the OP, in both seven month periods all NG and electricity utilizations included. The only thing changed in my system is the boiler and comparing the seven month period is based on the actual utility bills.

Because we're comparing 2019 boiler to 2020 boiler which experienced similar winters, not 2019 house to 2020 house. To meaningfully understand percentage savings related to the boiler we should exclude non-boiler related gas consumption. It would be similar to comparing a car fleet's gas consumption when you replaced one with a hybrid. Maybe the fleet's consumption dipped 5% but on a new car to old car basis, consumption was cut by 50%. In this case, it's not as dramatic of course because the boiler is the majority gas consumer, but still helps with accuracy.

While cherry picking three, or seven month for that matter may not seem fair to you, I respectfully disagree.

Fair enough. Going in, I'd expect colder months to show less savings due to higher system temps and having a smaller oversize penalty compared to an older, non-modulating boiler, which is exactly what you experienced. That's why I recommended trying lower flow rates and a reset curve that's not as steep. That said, your utility still charges for gas in March through November, so savings then matter.
I don't think 7 months is cherry picking if that includes the all of the year's HDD days. Maybe it should be renamed HS(Heating Season) FUE! Make it easier to understand.

Skyline

Hot_water_fan said:

Because we're comparing 2019 boiler to 2020 boiler which experienced similar winters, not 2019 house to 2020 house. To meaningfully understand percentage savings related to the boiler we should exclude non-boiler related gas consumption. It would be similar to comparing a car fleet's gas consumption when you replaced one with a hybrid. Maybe the fleet's consumption dipped 5% but on a new car to old car basis, consumption was cut by 50%. In this case, it's not as dramatic of course because the boiler is the majority gas consumer, but still helps with accuracy.

There's no way to accurately exclude non-boiler related energy utilization, NG or electricity, nor was it intended to do that. The intent had been all along is to compare the impact of the new boiler to the system as whole. Again, the system in itself did not change, it still has the same heat emitters, appliances, comfort settings, etc. Comparing seven month periods of the utility bills for the same system with two different boilers is fair in my view.

The other intent had been to show, that most of the contractors/manufacturer had been full of... false statement. Saying that they had overstated the savings is an understatement. The $87.94 saving in seven month, compared to a non-condensing boiler, is practically nothing especially if the the cost of installing the new boiler is taken in to account. Maybe the next 4 - 5 energy utilization results in more savings, but that remains to be seen....

Hot_water_fan

@Skyline This is a public forum where people can learn about heating systems. A lot of what I'm explaining to you is not just for you. To make this individual experience applicable to others, I'm explaining generalized concepts. One concept is that boiler fuel usage is directly correlated to heating degree days. Another is that there is some usage that's not related to this: this mostly entails DHW, cooking, drying, grilling, etc that no boiler can save (sometimes with DHW). This number can be estimated pretty accurately! You can take summer usage (no HDDs) or run a linear regression to find the intercept if you have the data. In your case, you saved a significant percentage of gas/HDD. However, the dollar savings didn't meet expectations. It's important for you and others to focus on units of gas saved since gas costs change frequently and not all money spent on gas is volume based (some is $/Day, $/billing cycle, etc.). In your case, gas unit prices drastically increased which is why it appears you "only" saved $87.
A neighbor of yours with a 3x higher heat loss home could have installed the same boiler in the same climate and had drastically higher dollar savings but the same percentage savings. This is why I'm so interested in percentage savings - they can help others! In your case, the installers misled you - they didn't do their homework to determine what was reasonable fuel savings. They also installed a boiler with high electricity usage (due to restrictive heat exchanger) and paired it with an electrically intensive distribution system. These are choices that others can avoid in the future.

Skyline

Estimates are just that, someone slapped his/her belly to come up with a number. I deal with concrete numbers that are on the utility bills. In this thread, both the percentage of energy utilization, cost savings, HDD for both years, etc., had been posted. Comparing the two boilers in the same system with all of the variable accounted for in both cases is fair.

I did learn a lot about heating in this forum, but it's enough learning from this thread...