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New to combi-boilers...

Skyline
Skyline Member Posts: 116
My 20 years old Triangle Tube Phase III had been replaced with Viessman 222-F Model B2TB 35-125 with NG. While I debated pushing out the replacement to next year, the Phase III had sprung a leak internally, there was no choice, but to do it this year.

It's been four days the 222-F providing DHW and it does that with ease. The 26 gallon reserve tank is really great. Even if the boiler is off, there's still DHW for a good while. Just like the Triangle Tube used to do.

Last night was the first time, that the heat actually kicked in at five in the morning in zone #1, thermostat set @70 degree. To say that the combi-boiler works differently is an understatement...

At 05:30, I've seen the boiler running at 14% capacity and zone #1 circulator running. A bit later, this is what the display showed:



About an our later, the display showed:



In both cases, the burner is off, but it was captured about an hour later:



I do not know how many times the burner was on and how long. Is there a way to capture this information? Well, other than sitting front of it that is...

With the heating slope set to 1.4, it took the boiler three hours to increase zone #1 temperature from about 67 to 70 degree. I've seen somewhere, that the optimal heating slope for this boiler is 1.3. Setting the slope to optimal would increase the time to reach the set temperature, correct?

My old boiler would have increased the temperature in zone #1 in less than hour, given the same circumstances. While it had always fired at 100% firing rate, I am not certain that doing the same in three hours would cost less. At least, not substantially less. Would that be correct?

The answer does not really matter in my case, since there was no choice, the Triangle Tube had to go...






Comments

  • Ironman
    Ironman Member Posts: 6,587
    Using setback is counter- productive to the logic of a mod/con; it will actually use more fuel that way. Leave the stats at one constant temp where you're comfortable. Set it and forget it.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    fenkel
  • Skyline
    Skyline Member Posts: 116
    It is more comfortable to sleep in 65-67, than 70 degree room temperature. If the setback is counter-productive, so be it.

    With that said...

    I don't like how long it takes the mod/con boiler to go from 65-67 degree to 70. The boiler efficiency might be 90-95%, but it will probably use as much NG during the 3-4 hours, as the old non-condensig boiler did in an hour to reach 70 degree.

    That's just for the NG utilization. Having two circulators, one internal in the boiler the other is for zone #1, requires power as well. The cost of constantly running them for 3-4 hours will show up in the electric bill, that may even offset whatever the mod/con boiler have saved in the gas bill.

    Is there a "happy middleground" with the mod/con boilers, where efficiency is a OK and recovery time cut in half at least?

  • flat_twin
    flat_twin Member Posts: 292
    edited September 2020
    Don't worry about 3 hours to recover from night time setback. Just bump the time the 70 degree setting begins. If you want it to be 70 degrees at 7am, Set the boiler to begin daytime temp at 4am instead of 6am. Modcons are at their best running long cycles at lower supply water temperatures. Additional run time from two circulators is more than made up for in heating efficiency.
  • psb75
    psb75 Member Posts: 479
    Choose your settings wisely and carefully. Set...then forget. Let the boiler do its own "thinking". You can adjust the curve if you want to. Let the outdoor reset "do its thing." You are correct in noticing that this boiler is a totally different "animal." It "knows" efficiency better than you do.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,970
    edited September 2020
    Just because you've "seen somewhere" that a 1.3 heating curve is optimal, it doesn't mean it's the correct heating curve for your house. Increase the heating curve until you're comfortable.




    Often wrong, never in doubt.
  • PerryHolzman
    PerryHolzman Member Posts: 234
    I have a Vitodens 200 from 2006 with external water heating. I had to change the heating curve settings and some time settings for when hot water was available to get things to work correctly from the defaults and original set-up. It took going through the 1st winter to get things right; but have never changed those setting since early 2007 - it really works well.

    I left the night setback on manual (I can switch to day or night on my living room control). I rarely use it as the upstairs bedrooms are normally a few degrees cooler than the main floor. I most often use it when going on a trip.

    I wish you well with figuring out how to adjust your system so it automatically does what you want.

    Perry
  • Skyline
    Skyline Member Posts: 116
    The 1.3 that I've "seen somewhere", was not related to the heating curve. Instead, it is related to the combustion chamber's air to fuel ratio as explaind in the introduction video for the 222-F.

    The outdoor temperature is in the mid-40s at five in morning, when the "wake up" cycle starts. I do not know what the zone temperature is at that time, nor do I know the initial burner utilization rate . By the time I get up around six, Zone #1 temperature is 68-69 degree. Getting to the 70 degree takes an hour or two more, depending on the outdoor temperature rise rate. This is the time, when the display shows 14% burner utilization rate, or ~19MBH input.

    The burner isn't always on during this this time. Presumably, it cycles on and off a number of times. I do not know how often this takes place, or how long the burner is on, when it's fired up. Is there a way to get this information out of the system?

    Running two or three circulator pumps, I have two zones, with the energy efficient boiler for three-four hours could cost more, than the actual fuel cost. It does depends on the utility rate, my state has the highest in the US.

    What is the result of changing the heating curve from 1.4 to 1.x, 2.x, or even 3.x? Judging by Alan (California Radiant) Forbes' image, the water temperature progressively increase/decrease with the heating curve changes. Do the sections in A, B and C in the image indicate the boiler operating efficiency, or condensing/non-condensing?

    The heating curve and other values presumably had been changed from the defaults to the installer's own recommended settings. Until I know the results of any of the available changes, I am not going to change anything. Knowing just enough to mess up everything is a dangerous position to be in.

    The temperature in the house is even all around, without the swings that the old boiler had. There's no urgency to change it, I am just evaluating the various options.

    I will also participate in Viessmann online seminars about this system, just to be more dangerous... ;)B)













  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,970
    edited September 2020


    These refer to the water temperatures on the y-axis.

    With the heating slope set to 1.4, it took the boiler three hours to increase zone #1 temperature from about 67 to 70 degree. I've seen somewhere, that the optimal heating slope for this boiler is 1.3. Setting the slope to optimal would increase the time to reach the set temperature, correct?

    When you say optimal, do you mean optimal comfort or optimal efficiency? Optimal comfort will cost you more.

    If you're happy with the current setting, leave them alone.
    Often wrong, never in doubt.
  • Skyline
    Skyline Member Posts: 116



    These refer to the water temperatures on the y-axis.

    When you say optimal, do you mean optimal comfort or optimal efficiency? Optimal comfort will cost you more.

    If you're happy with the current setting, leave them alone.

    Thanks for legend...

    Sounds like it's an either or choice. Basically, if I set the heating curve to the 3.x, there's optimal comfort, but this boiler will not condense in that case. Conversely, if it set to 1.x, the boiler will condense, but also take 2-3 hours to heat up the zone at hand.

    I have two zones, one with cast iron radiators, while the other is baseboard with fins. In both zones, the optimal comfort is 70F during the day and 66F at night. We work from home and also have grandkids couple of times a week. At times, the night temperature setting is temporary changed for the grandkids.

    In retrospect, maybe a non-condesing boiler with DHW would have been a better option for me, than the Wiessmann 222F. Unfortunately, every contractors (six of them) except one were quoting mod-con boilers. The non-condensing boiler quote wasn't much less than the Weissmann, one of the reasons why I went with the 222F.

    Oversold on the possible savings? You bet...

    All all of this does not mean I have remorse. The 222F is a great boiler, quite and provides plenty of DHW for our needs. We'll see how it'll handle the heating season soon enough...
  • Even with your heating curve at the lower end of 3.X, your boiler will still condense with outside temperatures above 45°F when return water temperatures are 130°F or below.

    Play with your curve and see if you can be comfortable at a lower heating curve number.
    Often wrong, never in doubt.
  • Skyline
    Skyline Member Posts: 116

    Even with your heating curve at the lower end of 3.X, your boiler will still condense with outside temperatures above 45°F when return water temperatures are 130°F or below.

    Play with your curve and see if you can be comfortable at a lower heating curve number.

    Thanks Alan...

    Does the boiler monitor the return water temperature (RWT) and cycle the HX as needed for condensing? For example, if the RWT reaches say 125 degree, it'll shutoff HX and will fire it up, if the RWT drops to 100-110 degree.

    That would make sense, if the boiler is condensing. Otherwise at 45 degree outside temperature with the heating curve set to 3.2, the supply water temperature (SWT) will be at ~154 degree. Depending on the flow volume/speed and radiators' heat tranfer rate, the RWT may rather quickly reach 130 degree. That might not be the case with seven castiron radiators of all different sizes, but the baseboard may get there in a hurry. High output or not...

    Maybe that's what you meant with "play with it", find the "sweet spot". Find the heating curve most suitable for the purpose that pretty much will be a compromise between comfort and efficiency.

    In my neck of the wood, the electric bill cost about twice as much as the NG bill, from my September bills:



    The 222F had been installed about two weeks ego. While the NG usage didn't change, the electricity utilization increased by 6.3%, when compared to last year. Albeit removing the old and installing the new boiler did require using power tools, that could had been one of the contributing factor for the increased power utilization.

    When the heat is on, nominally the internal and zone circulators use close to 200W. I can check the actual usage on the UPS, once the heat kicks in again with the current settings.

    Running both of them for 3-4 hours might be counter productive and may offset whatever the boiler is saving by being roughly 10% more efficient, than a non-condensing boiler.

    Maybe I am wrong, actually, I hope I am wrong. In either case, I'll keep a close eye on both of the bills, just to see how the new boiler impacts these bills...


  • hot_rod
    hot_rod Member Posts: 15,055
    it sounds like you are just concerned with ramp up coming out of setback? If so, as @flat_twin suggested, back up the start time.
    Electrical consumption? What type of circulators? if they are ECM, I'd guess less that 100W for both.
    It's really more about the type of heat emitters and sizing that allows you to run condensing conditions always. IF you could heat the home comfortably with 120F- 130F on design, then it would condense all the time.
    To get that operation you may need to add or upsize heat emitters. that is really not a boiler or boiler brand issue, but a match between heat generator and heat emitters.

    This may clear up that
    :)https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Skyline
    Skyline Member Posts: 116
    hot_rod said:

    it sounds like you are just concerned with ramp up coming out of setback? If so, as @flat_twin suggested, back up the start time.
    Electrical consumption? What type of circulators? if they are ECM, I'd guess less that 100W for both.
    It's really more about the type of heat emitters and sizing that allows you to run condensing conditions always. IF you could heat the home comfortably with 120F- 130F on design, then it would condense all the time.
    To get that operation you may need to add or upsize heat emitters. that is really not a boiler or boiler brand issue, but a match between heat generator and heat emitters.

    This may clear up that
    :)https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf

    My concern is about the length of the ramp up time and the related energy utilization.

    Yes, the two zone circulators use less than 100W. On the other hand, the boiler in itself uses more:


    The power consumption is for B2HA series boiler, but it is the same for the B2TB series, as stated by Wiessmann's tech support. Getting the power utlization was necessary for determing the correct size of the UPS backup for the boiler. Quote from tech support:
    Yes, 900W looks like it's plenty sufficient. The largest size 222 (the 35 Kw unit) running at full bore with the burner running at high fire and both built in pumps running, is approx 232 watts. That plus the 90 watts from your pump and the minimal watts from your condensate pump, it sounds like that should work fine.


    The quoted max power consumption is around 350W for the system, that probably seldom reached. The more reasonable consumption is around 200W in heating season. Tested the my 1,000W UPS with DHW only, it showed 60W power utilization, with the burner running at 40% utization. The UPS would have provided the backup for this load for 55 minutes. With heat ru8nning, this will probably drop to half, or less.

    My radiators are probably the same age as the house, which is around 70 years old. The baseboard is "younger", around 30 years old.

    Thanks for the link, it's an interesting read for a layman, I learned from it and will continue reading the document. Despite that, I am not about to have the heat emmiters redesigned and installed. That should had been addressed by the contractors who provided the quotes for various systems, but none of them did.

    One thing I consider, especially after seeing your video about the magnetic dirt separators. Presumably, the separator can be retrofitted in to my system. Can you recomend the right one for my system?

    TIA...
  • mattmia2
    mattmia2 Member Posts: 3,991
    I would be careful about sizing a UPS on the continuous power draw. Both motors when they start and some types of ignitors can draw 5-10x the running current when they start.
  • Skyline
    Skyline Member Posts: 116
    mattmia2 said:

    I would be careful about sizing a UPS on the continuous power draw. Both motors when they start and some types of ignitors can draw 5-10x the running current when they start.

    Generally, that is true, however...

    Based on the Wiessman tech support provided power consumption numbers, the worst case scenario is about 313W, including the igniter, if the heat is running at full blast. Adding the two zone circulators, 44W each, makes it 421W.

    For the DHW, that shuts of the heat, it's about 180W. I do know, that the UPS has no issues with running the DHW from the battery backup, the boiler drawing around 60W. This has been tested.

    The heat probably will not run full blast either, so, my estimated ~200W average draw for the boiler sounds about right. During the 3-4 days cold snap earlier this month, zone #2 didn't even call for heat.

    The heat cyle's power draw remains to be tested with battery power, but the chances are that 1,000W UPS will be just fine.

    At least until it is tested... ;)

  • Skyline
    Skyline Member Posts: 116
    @mattmia2

    Tested the UPS backup operation today with the heat, by turning off the boiler with the switch and the breaker in the panel.

    Started up the boiler and it did its routine of testing the component. The power draw was between 140-150W at this stage for a minute or so.

    Next, increased the temperature via the thermostat for both zones. The boiler started the heating cycle and turned on both of the circulators. I did not see the inital draw for the startup, but it did start up without any issues. The continious power draw was between 210-220W and UPS estimated 33 minutes of power remaining. That's more than good enough for me...

    You scared me for a second @mattmia2 that I need to get a larger UPS....

    mattmia2
  • mattmia2
    mattmia2 Member Posts: 3,991
    "Universal" and small DC motors aren't as bad with inrush, but it can still be an issue. Induction motors typically draw x5 or more their running load when they start and UPSs and generators need to be sized to handle that.
  • Skyline
    Skyline Member Posts: 116
    @Alan (California Radiant) Forbes

    I've got around and studied/red about the heating curves and their impact to boiler temperature.

    The Wiessmann's manuals do make recommendations for setting the heating curves, based on the the type of heat emmitters. Mine is bracketed in red:



    From my perspective, the heating curve set of 1.4 is not adequete for the current outdoor temperature range. Nor do I believe that one heating curve setting would be suitable for the six month heating season.

    For my radiators, I have split the heating curve in to five settings as such:



    Based on the outdoor temperature ranges, the heating curve settings would be:
    • 41 - 50F: 2.0 (October, March)
    • 32 - 41F: 1.8 (November)
    • 23 - 32F: 1.3 (December)
    • 14 - 23F: 1.1 (January)
    • 5 - 14F: 1.0 (February)
    The intent of these settings is "optimal comfort and optimal efficiency", or as close to it as possible. My other zone has baseboard, that requires different settings for comfort where efficiency takes a backseat. Even, if the time zone #2 calls for heat, there's some condensing at the beginning.

    Changing the heating curve on a monthly basis isn't hard and does not take long. It can also be modified for comfort, if couple of days of cold snap, like Artic air hits the region.

    Am I on the right track?

    TIA...


  • mattmia2
    mattmia2 Member Posts: 3,991
    The Idea is that the curve takes in to account the heat loss characteristics of the building and sets the supply water temp based on the outdoor temp. If you choose the right curve, the right max and min supply temps and max and min outdoor temps it should find the right supply water temp automatically.
  • Skyline
    Skyline Member Posts: 116
    @mattmia2
    The heat loss charcteristic of the building is not something that can be set on the boiler AFAIK.

    As such, the curve progressively increases the boiler temperature in relation to the outdoor temperature. The program knows, if the outdoor temperature is dropping, the heat loss increases, regardless of the heat loss ratio of the building at hand. In most cases at least that is the case and certainly in mine.

    Isn't the min/max supply temps programmed in the unit, based on the outdoor temprature and curve setting at hand? Wiessmann's graphic posted earlier seems to imply that.

    For example, if the outdoor temperature is 41 - 50F range, the curve is set 1.4, then the boiler temperature max/min is 104/118F.

    Conversely, if the outdoor temperature is 5 - 14F and the curve is still at 1.4, the boiler min/max temperature is 144/154F.

    Wouldn't setting the curve in couple of temperature ranges keep the boiler temperature closer to the 130F? It does not meant, that it would be "optimal comfort", but it is a starting point for optimal efficiency purposes.

    Am I looking at it wrong?

    PS: This is my understanding how the heating curve works, please correct me, if that is wrong.

  • flat_twin
    flat_twin Member Posts: 292
    edited October 2020
    Get used to the idea that it's going to take a full heating season and maybe two before you have the outdoor reset dialed in. The suggested boiler temps for cast iron rads is just a starting point. Our Weil Mclain modcon had similar suggested temps in the manual for cast iron rads.
    If your house has had updates to windows, doors, insulation etc over the years you can likely run the boiler on much lower supply temps than the manual suggests. Based on the chart you provided above, my house (10 cast iron rads, old pipes, 1780 sq ft, built 1835) would be good with the curve marked "0,8" , max supply temp of about 140 at -20 outside.
    I have dialed down our outdoor reset to the point that it worked fine on a sunny calm day but a cloudy windy day was enough to make the boiler lag behind the heat loss and the indoor temp couldn't keep up. Once I found that point I just added a couple degrees to the supply temp to cover those conditions. The boiler runs long cycles and is condensing all the time other than during a DHW cycle.
    You can make an educated guess at where to start but it's only by making small changes as the winter goes on that you'll know what works best. Also, you don't need to change the curve every six weeks. The idea is to have one curve to handle the outdoor temperature swings for your area.


  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,970
    edited October 2020
    You have two zones. One has cast iron radiators and the other has copper fin tube baseboard (BB). Referencing the Viessmann graph, you have the cast iron zone in the "B" category and the BB zone in the "C" category.

    Ideally, you install enough BB to keep the room warm at the same water temperatures that will satisfy the rooms that have cast iron radiators. This is probably more than you currently have now and it may be hard to do because all the BB is existing and you don't want to spend the time or money to change it.

    The next best scenario is to install a mixing valve for the cast iron zone which will effectively allow you to have two heating curves, one for each type of emitter. The advantage is that both zones will be getting the water temperatures they need to keep you warm (optimal comfort). The disadvantage is that your boiler will be firing off the higher curve, i.e. not optimal efficiency.

    The heat loss charcteristic of the building is not something that can be set on the boiler AFAIK.

    Between the heating curve and the parallel shift, you should be able to get close.

    Wouldn't setting the curve in couple of temperature ranges keep the boiler temperature closer to the 130F? It does not meant, that it would be "optimal comfort", but it is a starting point for optimal efficiency purposes.

    You keep on asking the same question. The answer has always been "yes". Try programming the boiler at a 0.2 heating curve. It will be condensing all day and there will be huge savings in your utility bill, but you will be uncomfortably cold.
    Often wrong, never in doubt.
  • Skyline
    Skyline Member Posts: 116
    flat_twin said:

    Get used to the idea that it's going to take a full heating season and maybe two before you have the outdoor reset dialed in. The suggested boiler temps for cast iron rads is just a starting point. Our Weil Mclain modcon had similar suggested temps in the manual for cast iron rads.
    If your house has had updates to windows, doors, insulation etc over the years you can likely run the boiler on much lower supply temps than the manual suggests. Based on the chart you provided above, my house (10 cast iron rads, old pipes, 1780 sq ft, built 1835) would be good with the curve marked "0,8" , max supply temp of about 140 at -20 outside.
    I have dialed down our outdoor reset to the point that it worked fine on a sunny calm day but a cloudy windy day was enough to make the boiler lag behind the heat loss and the indoor temp couldn't keep up. Once I found that point I just added a couple degrees to the supply temp to cover those conditions. The boiler runs long cycles and is condensing all the time other than during a DHW cycle.
    You can make an educated guess at where to start but it's only by making small changes as the winter goes on that you'll know what works best. Also, you don't need to change the curve every six weeks. The idea is to have one curve to handle the outdoor temperature swings for your area.


    One of the installer stated, that it took him three heating season to dial in the outdoor reset. I am not certain that I'd want to wait that long.

    My house is 1,300 sqf with seven CI rads with old pipes in zone #1 and a single BB in zone #2. Replaced the old windows, AL siding, improved the insulation all around about 6-8 years ego. Since then, zone #2 seldom calls for heat and the temperature in zone #2 is 65 - 68F. The tstat in this zone is set to 67/64F for day/night. This area does get some air movement from zone #1, you could say that it gets most of the heat from there. We did need zone #2 prior to improving heat loss in that zone. By now, we probably could leave the tstat off during the heating season.

    In my neck of the woods, we seldom see zero, much less minus temperatures. For example, in the last heating season, the average temperature in December, January and February was in the 36F range. In February, we may get couple of days in sub-zero temperatures, but that's the exception not the rule.

    Here's my NG utilization for one year, includes heat, DHW, cooking and dryer:



    Last heating season, I had a non-condensing boiler with 82-85% energy efficiency.

    The 0.8 curve is good for -20 outside, but at 36 outside the supply temperature is around 100F that will take at least 3 - 4 hours to increase temperature inside couple of degrees. My idea was, that set the curve to 1.8 for the 36 degree outside, resulting in supply temperature of 122. That extra 22 degree temperature would shorten the time to increase the temperature couple of degrees inside, while still keeping the boiler condensing.

    Power, or electricity rate is the second highest in the US for my neck of the woods. It is more expensive than the NG and as such, I'd want to cut the time to heat up the house. I'd pay roughly twice as much for electricity, than for NG.

    While it may seem that the boiler does not use much power, it actually does, if and when it runs 4 - 5 hours. I see it on my UPS, that the boiler is using 180 - 230W during this time. Once the "kill-a-watt" arrives, the actual cycle's power utilization will be measured and recorded.

    I could leave the curve at the current 1.4, or even change it to 1.8 and leave it alone. The boiler would condesate most of the times and have long cycles, so-so comfort and the NG bill would probably be less than last heating season. On other hand the electric bill would increase substantially.

    Finding the balance between comfort, energy utilization and efficiency is the point for my given circumstances. Trying to understand how the boiler works, what impact the outdoor reset has on curve, how the boiler temperature changes, etc., helps for achieving that. Wiessmann's outdoor reset, curve and boiler temperatures charts are helpful from that respect.

    Advices of "optimal comfort or optimal performance", just increase the curve 0.2, etc., on the other hand not so much...









  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,970
    edited October 2020
    My idea was, that set the curve to 1.8 for the 36 degree outside, resulting in supply temperature of 122.

    Finding the balance between comfort, energy utilization and efficiency is the point for my given circumstances. Trying to understand how the boiler works, what impact the outdoor reset has on curve, how the boiler temperature changes, etc., helps for achieving that.

    Sounds good. To tell you the truth, I've never thought much about electrical usage for a system. I figured small, 1 amp pumps wouldn't amount to much. I'd like to hear what you find out.
    Often wrong, never in doubt.
  • Gilmorrie
    Gilmorrie Member Posts: 147
    edited October 2020
    The electric power used by the circulator pump is not wasted. All that energy has to go somewhere, and it winds up as heat added to your system - which then goes into your home - and offsets your regular fuel consumption.
  • hot_rod
    hot_rod Member Posts: 15,055
    Many will agree indoor reset is as or more important than the ODR. A drop in outdoor temperature doesn't necessarily mean the building load is going up. High mass systems especially benefit from this control logic.
    tekmar has promoted the two logics working together for many years. Here is a quick read.

    http://www.tekmarcontrols.com/support/tekmarglossary/33-support/glossary/168-indoorfeedback.html
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Skyline
    Skyline Member Posts: 116

    Sounds good. To tell you the truth, I've never thought much about electrical usage for a system. I figured small, 1 amp pumps wouldn't amount to much. I'd like to hear what you find out.

    Monitoring power utlization of the 222-F is in its early stage, not much data yet, but here it goes:



    My intent had not only been to track power utilization, rather, to study the impact of the heating curve changes. This is how I've learned, that the curve set to 1.4 is not suitable for the outdoor temperature of 54F. The SWT of 88F for zone #1 is too low and takes long time to heat up the zone. In my view, by 11:30AM the increase in outdoor temperature was more useful than zone #1 being active.

    After changing the heating curve to 2.0, the heating cycle is much shorter, the zone feels comfortable and yet, it still condenses at RWT of 115F.

    What's not in the image above, is the fact that on the second day, the overnight temperature dropped to 45F and the heat was probably on in the wee hours of the night. When I got up in the morning around six, the zone was comfortable and the heat was not on. Unusual, but zone #2 came on as well. Happens when your better half leaves the window open.

    There isn't enough data to draw conclusion in either direction, but it'll come with time.

    On the other hand, it'll be a good excercise to learn about heating curves impacts on SWT/RWT in relation to the outdoor temperatures.





  • Skyline
    Skyline Member Posts: 116
    @hot_rod

    I've seen that page awhile ego....

    The content of that link had been "above my head", but now, it started to make sense. Thanks...
    mattmia2
  • Skyline
    Skyline Member Posts: 116
    It's been one week that "Kill-a-Watt" is collecting boiler's power utilization data. It's not much, nor did the heating season really started up yet. The results are a mix bag as far my earlier projections are concerned:



    Does the boiler use lot of power? The short answer is yes and no. It is highly dependent on heating curve setting, that depends on the outdoor temperature to set the SWT for the zone.

    For example...

    Look at the October 8th record, where the outdoor temperature was 54F, heating curve 1.4 and the zone SWT around 90F. The thermostat in zone #1 did not go off for 5.5 hours. In that 24 hours period, the boiler used 1.29 KWh.

    The very next 24 hours period, after the heating curve changed to 2, the zone thermostat called for heat for two hours and subsequently, the boiler used 1.12 KWh in this period.

    The other three days with heat on were working similarly to the second day, but did not match the first 24 hours period power utilization. October 13 came close to it, the thermostat called for heat twice during this 24 hours period and circulators ran for the total of about three hours.

    There were two days, where I did not see the thermostat calling for heat, these days are DHW power utilization only.

    So, yes, the boiler can use more electricity as it should and keep the zone comfortable. At this outdoor temperature ranges and heating curve setting, I anticipate the monthly electric bill for the boiler will be in the $6-7 range. It's not a lot, but it is early in the heating season and remains to be seen what the power utilization will be for January and February.

    Having a single heating curve setting is not suitable, at least for my purposes and if I want to keep power utilization in the necessary range. There are two options, based on Viessmann tech support reply, quote:

    You can certainly have a fixed setpoint for your heating system but the temperature you are requesting may not be sufficient when the cold weather returns this winter. If the issue is mainly the use of the heating curve and it is not providing the necessary temperature to recover your thermostat in a timely manner, the two options are to 1) raise the heating curve to get the recovery time you desire, or 2) you can set a fixed temperature to the temperature it would take to heat your home on the coldest day of the year.

    Option 1 provides the more efficient operation in terms of fuel. The 2nd will essentially turn your boiler into more of a conventional type boiler, such as your previous boiler.

    Yes, I could just set a single heating curve to account for the coldest day in the upcoming winter. But...

    I did not pay for the installation of this Viessmann boiler to run it as a non-condensing boiler. I want to have the boiler condensing as much as possible and limit the use of electricity to what is necessary. The only way to achieve that is the different outdoor temperature ranges having different heating curve settings.

    Monitoring power utilization for the boiler been an interesting exercise, that brought out more data than was initially sought after. Once the heating season is in full force, there will be more data and quite possibly, more adjustment to the heating curve.

    PS: The boiler power utilization is somewhat skewed, there's a UPS between the "Kill-A-Watt" device and the boiler, that also use power. Mainly for cleaning the utility power and keeping the battery fully charged. My guess it uses about 0.03 KWh, or less.