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Bad news for condensing purists...(ME)

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Check this out. It would appear that the contingency of people who say that mod con boilers should NEVER be used on baseboard convectors are going to have to re-evaluate their ways of thinking...

I've always said this, now the government backs it up.

Read'em and weep, or would that be condense:-)

Makes me wonder why manufacturers would even consider making anything other than a mod con appliance...


Comments??


ME
«1

Comments

  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
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    I never could figure out the resistance either.....

    With 95% of the heating season at 60% or less load, this means that for 90% of the heating season a 180F baseboard can operate at 140F or less. I'm glad a study was finally done. Also baseboards DO WORK with full reset!

    Boilerpro

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  • Unknown
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    thanks for the heads up mark, looks like some good reading!
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Believe that's the same study that Brad White posted here sometime last year--maybe even before.

    If so, read carefully and you'll find that most of their conclusions regarding operating temperature are based on maintaining space temperature and that daily setback could easily result in a significantly higher temperature requirement.
  • Mark Hunt
    Mark Hunt Member Posts: 4,909
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    Thanks for posting this


    I can honestly say that I have not offered anything but modcons for the last 7 years.

    In EVERY instance our customers saw dramatic reductions in their fuel consumption with NO adverse impact on comfort. I just got an e-mail from a customer the other day that confirms this yet again. HWBB DOES work with lower temp water AND OD reset.

    Thanks again Mark.

    Mark H

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  • Mark Hunt
    Mark Hunt Member Posts: 4,909
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    Set back


    I worried more about slower response times in our systems. None of the systems we installed have a "boost" function on them so the HWS temp is limited by the OD temp. The boiler controls do not over-ride the target temp.

    I have not had one issue regarding response time and ALL of my customers use set-back stats.

    Again, in every instance where we used modcon boilers with HWBB, the fuel usage reductions were significant.

    Mark H

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  • Brad White
    Brad White Member Posts: 2,398
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    Same Study

    that I posted about a year ago but definitely worth re-posting. Maybe Dan can put it in the library?

    I was not the first to post it, not by a long-shot. Someone else did and I found it compelling. As you noted, what is key is outdoor reset being faithfully observed against the number of hours when lower than condensing water temperatures can work very well.

    The study applies even to systems where baseboard was sized at conventional 180F water supply temperatures, knowing that at higher ODT's the water temperature will be low enough to start condensing.

    I still find it advisable in new designs to size radiation for 140F entering water (120 to 130 average depending on Delta-T of design) but for retrofit applications where 180 F was the basis, it still can show a payback. Cool.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Joannie_13
    Joannie_13 Member Posts: 6
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    From A Manufacturer

    I hear you, Mark! And, we wonder why anyone would want us to manufacture anything but mod-cons. Heck, people still insist on atmospheric units...with standing pilots!

    I know that some of this is because of difficulties people have had in the field, some is because of perception, some is because of fear of the unknown, etc. Some of that is the fault of manufacturers. Some is the fault of installers that don't have the right knowledge or equipment. Heck some people around here just don't want to abandon that nice chimney.

    It is changing, but manufacturers are going to build what the market wants (try to, anyway) and the market still wants 80% with thermocouples. Luckily, though, the market now wants mod-cons more than ever, so we're going in the right direction.

    :-)
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,944
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    It defied common sense

    Some people just REFUSE to be wrong - great info ME. Mad Dog

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  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,944
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  • Unknown
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    From a manufacturing standpoint

    I just submitted an article to a trade Publication discussing this exact topic. I think we ALL have known for a long, long time that utilizing Outdoor Reset can provide for optimum efficiencies and comfort provided the system can operate at these temperatures on design days or even moderate temperatures. Unfortunately we have been fighting the resultant issues of possible flue gas condensation when using too low a curve. Now with the advent of Modulating/Condensing boilers and Outdoor reset, more and more of those benefits can be derived because the boiler heat exchanger can now handle the condensation.

    I do have some issues with this test data though. I'd be curious to know the actual heat loss of this structure as compared to the 115 lineal feet of baseboard. In my mind it seems to be a bit overradiated as compared to IBR standards. We all know that with more radiation you can certainly use lower water temperatures just as I do in my home and we all know that a larger heat exchanger in a hydroair air handler will allow for lower water temperatures. In reality though, many existing homes are not necessarily overradiated nor do they have modified hydroair heat exchangers so careful analysis will be neccessary to determine if this average home will appreciate benefits such as stated in this article.

    One other thing that I see no mention of is tha temperature they were targeting in the Indirect heater. It would have to be somewhere in the area of 110°F or so to have return temperatures of 101°F and supply temperatures of 154°F. the question here is does the average home utilize 110°F domestic water? If it were a public facility it would be at 110°F but realistically we see tank temperatures of 130-140°F or so to be the standard to appease the homeowners. If I told my wife she could only have 110°F shower water she would file for divorce!

    I'd like to see test results utilizing less conservative temperatures for the indirect and more realistic footages of baseboard radiation. I'm quite sure the results would still be very good though. I'd be curious to know the heat loss and tank temperature though.

    Glenn Stanton

    Manager of Technical Development

    Burnham Hydronics

    U.S. Boiler Co., Inc.
  • Perry_3
    Perry_3 Member Posts: 498
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    From a homeowners perspective:

    As many of you know... I insisted on a high quality Mod Con last year for my Cast Iron 1950's era Monoflow T baseboard system.

    Overall estimated energy savings are somewhere between 40 and 45% (I had a long "discussion" with the gas company about how much gas I actually used during the "defective meter?" period after the boiler was replaced until the new meter was installed. They gave ground - but I ended up paying for more gas than the meter indicated).

    Of course it was not cheap to instal as the only way I could get it installed was on a T & M ++ based agreement as the HVAC contractor only wanted to install an old atmospheric type boiler and did not know much of anything except that his prior experience with a Munchin left him anti mod-con.

    I understand he has installed a few more mod-cons since my installation.

    Perry
  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
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    Related topic

    Outdoor reset works great with baseboard even when coupled with an atmospheric boiler. You don't get the full advantage of running condensing temps and you have to pick and choose your atmospheric equipment..... BUT!.......it does work nicely.

    I installed a Buderus 334 with their 2107 boiler control in a 6 unit apartment building using baseboard a few years ago. I sized the BB using an output of 500btu/ft and I let the control take the boiler water temp down all the way to WWSD temps. No "floor" whatsoever. The control shuts down circulation during burner firing when water temp is <104* but allows the temp to drop well below that during mild weather.

    All I can say is that it works. Those lads at BNL are preaching to the choir. Fixed firing rates and water temps should be relegated to the scrap heap of heating history.
  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    Setback

    I say let the system take care of it self...over the past year all of the systems (Baseboard) that I have been apart of, (that have had setback stats) we convinced the homeowners to do away with any "Set Backs"....
    The systems work great. We have to educate the home owners on how the "new system" will work. -Gpex
  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
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    Preaching to the choir and cranking up the heat

    And here's how to make a lecture sound like a sermon on the efficient ramble. You'll see how I love boiler manufacturers more than scientists - boilers make it steamy.

    I have always loved the simple beauty of fin tube baseboard. It works. It is painless and as far as hydronics goes it is quite unobtrusive even with the need to over-radiate for handling low heat. American genius on display. On hot temperature operation they do offer radiant output - the cowl gets all hot and radiates - on cold temperatures they become mostly all about convection without the forced draught. It's all perfect as we need ostensibly less radiant power in the shoulder seasons anyways.

    Of course, forced air delivers convection only heat which comes with lower yet temperatures and... the lower set of system wide operation efficiency (warehouses with hanging forced air furnaces are hard to afford next to their radiant competition. I know that)

    Does condensing mode work on forced air? Sure does, it even renders more condensed smoke as return air temperatures are as low as cold room temperatures 65 - 70 F. Hard to beat on condensing hot water. And yeah, 212F returns on steam don't exactly break a sweat at the boiler. But hold on, don't jump to conclusions and think the forced air furnaces must be more efficient than their hydronic competition.

    I say all this just because, I my opinion, it is not the low temperature supercondensing powers that explain why modern boilers are so good. Grasping at fumes returns a real dividend on fuel purchases, but the amount is not significant enough to explain the black magic we see coming out of our newer boilers.

    Let's mention the mod feature

    Modulation itself doesn't mean much - all boilers and furnaces that aren't run full blast all season long are on a modulating diet. How we modulate is the key. Modern boilers come with prepackaged brains in the form of electronic heating curve control. Old boilers and furnaces don't do that. This is a huge difference.

    The difference I am talking about is of course what results in nasty and costly overheating of the indoor space. Just as much as you and I all know how much is saved by turning down the thermostat, we can imagine how much is wasted on cranking up the room temperatures. It isn't even a simple relation, it is exponential: overheat up to 95F and mortgage your home to your utility.

    The study we're talking about compared a condensing boiler that came on only during heating demand times (see page 24 item 1) to a conventional boiler that remained at hot temperatures throughout the winter season whether home heating was needed or not - this is a crazy near zero limited modulation that yields monstrous waste. Sadly I know a bunch of places that run hot water exactly like that and I wish I could help them.

    Anyhow, just because of this, I think the study does not accurately represent how much is cashed back on condensing, but rather it shows what modulation does for starts. It shows what the combined use of an outdoor reset control and a condensing boiler does to hot water heating, but the study does not break down what is due to flue gas condensate and what is due to smart control.

    Credit is due where it belongs

    Modern hot water heating benefits enormously from both smart boilers and smart distribution schemes. Thank the brain.

    I am sure also, that if we were to lobotomize the control module on a modern appliance to then transplant it to the olden existing boiler in the basement, that we would see a good chunk of the same leap in system performance. This is of course a silly thing to do, but it goes a long way into explaining why hydronic systems have become easy to control whereas they were not in the past. All thanks to brainy electronics.

    Just because the fingers are itchy, I have to make a mention of what steam heat does. All the observed disaster stories stem from plugged loss of control, control that is very natural and very simple and inherent to the nature of cold seeking condensing steam and transfers of latent energy that are both irresistible and irreversible within the radiators. Steam comes to the job with it's own brains - hot water does not - not that this isn't either a huge problem to overcome, today, water is easily babied around to the needy radiators. Note also, that steam responds very badly to being babied like water, and respectively, water goes nuts with the lack of distribution constraints we see in steam systems. All that, and I have no problem with either hot water or steam. I just want the smarts with my heat.

    In many ways, I wish the topical study had looked into more of the whole system issues. The question they answered had a rather obvious answer right from the beginning. Any amount of condensation will yield a cash back bonus. Always. Just how much is a relative matter. Had they connected a condensing forced air furnace, bizarrely, the numbers and charts would have further outdone both their test subjects: they only looked at the appliances. They didn't look into the whole house and delivery-side radiator efficiency issues where cool temps are not so hot as they seem. Where forced air is not as hot as warm water and where neither are as hot as steam.

    My question

    Are there really many homeowners who object to using boilers with brains (whether built in modcon or custom controls)on any hot water application? I can't see why... Except for matters related to moderately higher initial cost and somewhat shorter life span and possibly costlier maintenance... and except for those who run the boiler full blast the whole winter even if not needed... like the people in this study did.
  • [Deleted User]
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    Jeeze Perry...

    I think you just set a record for the shortest post you've ever done, and you got your point across just as eloquently. :-)

    Let me guess. WIthin the next year, your previously single mod con contractor will have installed TWICE as many mod cons that year as he did his previous, and so on and so forth. Once people realize that it is an effective way to cut their gas bills in half, they'll ALL want one...

    Just a prediction mind you...

    Thanks for the input from a 'homeowners' perspective ;-)

    ME
  • [Deleted User]
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    Joanie..

    I understand. If you build it, they will come. SOme people (most heating contractors) are hard to get to change.

    It is great to see your company and many other staunch old line companies offering a condensing model. There are over 200 different models of mod cons on the European market.

    Change is slow, but change is good. Keep up the good work.

    ME
  • [Deleted User]
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    Gibby!!

    What you said. It's like trying to educate an American consumer to the "comfort number" system used on non electric TRV's. If they can't see a thermometer, they don't know whether they are comfortable or not :-) Forget what your brain and body are telling, they lie so much anyway. Gots to "see" the temperature in order to assure yourself you are COMFY!.

    We explain the non use of programmable set backs this way.

    The "energy savings" are coming from the high efficiency heat source. No need to suffer through set back in a common living space, and with the new ultra high efficiency heat source, it doesn't speak the same language as the programmable thermostat. System works best with the tempeoratures kept at a constant temperature. If your home benefits significantly from set back conditions, its an indication of more need for conservation (insulation and caulk and storm door/windows) anyway.

    Thanks for the great info pal.

    ME
  • [Deleted User]
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    Yeah but...

    And theseres a butt in every crowd :-0)

    Welcome back Grandpa. How's that shiny new grand kid doing?

    My partner had an 84% efficient Buderi boiler in his home (atmos-gas) with the finest Ecomatic controls. When he switched over to a non modulating (on ODR) boiler, he reduced his gas consumption an additional 30%. So did Dennis Bellanti, and so did I.

    THat is pretty danged significant. Not trying to bust on you. Just wondering why we Americans don't do as efficient a job as we can. I understand its budget driven, and generally speaking no one has money laying around waiting for thier boiler to break so they can throw 10 to 15 K at it, but you can pay me now, or you can pay the gas man again, and more and again and more...

    And I won't EVEN jump on the green band wagon. THose results should be fairly obvious...

    ME
  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    R U Comfy?

    I love to explain to consumers how TRV's work...
    It goes something like this: You turn this little dial to about "3"...thats about 70 deg.....if the room gets too cool turn the dial up a little, if you get too warm turn the dial down...when you find the place "Number" you like,
    lock the TRV in place and leave it alone.
    T-stat's should be thought of in the same way...find out the setting you want...and leave it alone. This is and alway's will be one of the hardest things to convince a consumer. -GPex
  • [Deleted User]
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    Further comparisons.

    Last summer replaced grossly oversized Am Std CI Atmospheric, w/ ODR & setback, w/ KN6 Hydrotherm Mod/Con w/ integral Tekmar. No set back. Degree Day compensated savings 30%.

    Replaced a too large National Atmospheric, w/ ODR & setback, w/ 2 PFG Atmospheric Weils piped parallel primary/secondary w/ Tekmar 264 Stager & set back. Degree Day compensated savings 20%.

    Anticipated better results from both jobs. Believe the reason for lower than expected savings was the old pieces, inefficient as they were, had ODR.

    Is a 10% savings split between single Mod/Con & staged multiple CI boilers a reasonable average number? Would set back have improved the Mod/Con's performance? How about staged Mod/Cons vs a single Mod/Con?







  • Brad White
    Brad White Member Posts: 2,398
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    I think you are hitting on

    the right nails there, Ron.

    The modulation -or in your latter case, staging-, pays more dividends longer than condensing alone.

    (As Mark E. pointed out by his own research at the end of the last heating season or the one before, night setback yielded no particular savings in his case. What was saved coasting down the hill was spent powering back up the hill, it seemed. Generally, I can see that and systems do vary, but I will accept that.)

    By running one of the smaller boilers (even if bang-bang on-off) for a longer period rather than cycling off a larger single boiler and suffering cycle losses each time, tells the story. Combined with ODR, or rather, you are staging your plant to that moving variable, is where the larger dollars are.

    Give me modulation over condensing alone.

    Or, to paraphrase Archimedes: "Give me modulation plus condensing and a place to stand and I will watch that darn boiler all day long."

    Brad
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • ALH_4
    ALH_4 Member Posts: 1,790
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    What I see as the reason acceptance of "high temperature" emitters as being appropriate for use with modulating/condensing boilers is that we tend to look at this snapshot in time that is the "design day". It's easy to forget that there are VERY few design days, and that the fluid temperature is lower 98% of the time.

    I am as guilty as anyone of thinking that baseboard was not an appropriate application for mod/con's. I (think) have seen the light. I learn more every day. ;-)

    Another variable that seems often ignored is firing rate. Even at 167°F, the Vitodens 200 condenses at 30% firing rate. So high temp emitters with a low heat load can still be 97% efficient, hence the importance of modulation with condensing boilers, particularly with high temperature emitters.
  • Unknown
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    how does firing rate affect dew point?

    more accurately, I don't understand how the firing rate affects condensation. I could see if you were running a very wide temperature differential, but firing rate?

    can you explain? I'd be very interested to know.
  • ALH_4
    ALH_4 Member Posts: 1,790
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    Firing Rate

    I am sure I do not completely understand what is going on, but what I think is happening is that at lower firing rates, the flue gas has more time in the heat exchanger to cool and condense when compared to higher firing rates.

    What I am guessing is that it has something to do with heat exchanger surface area compared to the burner size. Boiler heat exchanger sizing is a mystery to me, but I would assume heat exchangers are sized based not only on thermodynamics, but also on cost and size constraints. I am certainly not a boiler designer, and I am only guessing, but there has to be a reason for the behavior shown in this diagram.

    So now we have two variables affecting efficiency rather than just fluid temperature. Luckily they depend on the same parameter (outdoor temperature) in the same way.

    How are boiler heat exchangers sized?
  • Unknown
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    well, that's very interesting. Do you know enough to be sure that similar principles apply to anything other than the vitodens?

    Their "alien technology" has done stranger things that other boilers wouldn't emulate... but if they did... that's very interesting indeed.
  • ALH_4
    ALH_4 Member Posts: 1,790
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    I don't know...

    I know only what is shown in that diagram, and that Viessmann provides more engineering data than any other manufacturer I have seen. Therefore I assume other manufacturers have not bothered to publish this data for their customers. I assume this is a mod/con phenomenon rather than just a Vitodens 200 phenomenon, but I have no proof. It seems like efficiency increases in the condensing range must be due to flue gas condensation, which should be independent of the exact boiler model. I'm sure other boilers would not track those curves exactly, but they possibly would have very similar curves of their own.

    If anyone has more information, I would be very interested.
  • [Deleted User]
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    Thanks Brad.

    Real world means compromise. The 2- PFGs went in a condo where I had originally quoted a Mod/Con w/ CI for pickup above condensing temps. The board had a few real worlders who went CI for reasons other than price.

    Read Mark's post on set back. He said he was doing 10*. We did some experimenting @ the oil co. 30 years ago. 10* worked for scorched air. Water & steam were best in the 4-6* range. Didn't kill savings w/ long pickups. Then again, back then, everything was 2X too big.

    We've used set back w/ ODR on multi family since early 70s. Now that many of us are sizing to load, I think sensible set back is still a plus for that 90%+ of the season when we're not close to design. Particularly when the coldest part of 24 hours is @ nite, & your beast can burn 600 mbh. Bet we could have coaxed a couple % more out of that KN w/ set back.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    The "relative" scale of TRV operators is one of my favorite features. I've recommended to numerous people (homeowners and pros alike) that the user NOT have thermometers--even removing or covering them--and adjust the TRV operator for comfort and then LEAVE it there unless the space won't be occupied for days.

    I have an almost ridiculous number of thermometers throughout my house but I do my utmost not to use their indication as a measure of comfort. My personal winter comfort temperature (for mainly sedentary work) is about 65F with WET heat and about 67F with hot air heat. The only times I have problems with either are with prolonged cool, damp weather or in the shoulder seasons with relatively warm, clear days and clear nights with the temp dropping to around the freezing point.
  • PJO_5
    PJO_5 Member Posts: 199
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    What about this scenario?

    I had to choose between propane and oil nine years ago. Given the 40% or so higher BTU's in oil and having to park a gray submarine outside that the propane supplier owned (or I part w/ $$$) I chose oil. I also now burn B20, so that's a plus...and it works great with only a 5% cost increase.

    I have a mix of radiant and baseboard - almost 50/50 - and I do my own version of ODR down to 140F supply (w/ about 125F or so return when it's getting warm). I think dollar for dollar I am close to propane, but am losing some in efficiency (made up by oil vs. propane). I also think the slightly lower condensing temp of oil-fired vs. gasses (125F or so to 135F as per the article) helps a bit for protection of the boiler...

    As far as setback, I've opined before about my own situation...but here goes:

    I take very good advantage of passive solar, and because I tweak the boiler temp 2-3 times a day very often I get away with a nice setback routine...it isn't perfect and certainly not for everyone. My boiler rarely runs through the middle of the day most of the heating season...because of solar AND I set back the temps.

    The morning routine is when the boiler matches well; except for the warmest shoulder season, it typically runs for 30 minutes or more each cycle as the baseboard and radiant are both calling...radiant first and I shower and do the morning dishes and laundry many days from 5:15 to 6:00. I like it a little cooler, but by the time management gets up (7:15 or so) the house is warm enough for her ;-)

    When the baseboard calls about an hour after the radiant, the boiler cruises along at a very slow increase as all six zones are heating up. By 8:00 the house is toasty and the setback comes in by 9:00 as everyone leaves. It slowly cools for another hour or two - but if it's a sunny day it warms up again.

    By 2:30 p.m. or so it has "caught up" and often passed the 70F mark by itself most days with the passive solar and thermal mass...but if I had constant circ/temp settings the boiler would cycle, no? And it may be a little warmer because the radiation is still putting out some heat?

    This is whether I had a mod/con or conventional WITH the above control strategy...and with five circs the electrical savings is pretty substantial over the course of a year. I wish I would have done a couple more zone valves instead...

    At night during the shoulder seasons is when I am behind compared to the article. The boiler tends to cycle too much, despite a decent amount of volume (about 45 gallons total I believe). I setback the entire house between 3 and 6 degrees F, and the lower difference vs. outside is small but has to make a difference. When the house is warming up in the morning the outside air is also warming up some vs. a few hours ealrier as the sun comes up. To imporve the boiler cycles here, maybe I should hook up another boiler control in series w/ the one on there now like Hot Rod mentioned once to get a 25-30F differential...I'll add it to the "Honey-Do" list :-)

    I think everyone agrees that near design conditions almost any boiler is pretty efficient IF it is sized right and the radiation is correct...pretty big "if" ;-)
    The question is during the shoulder seasons - but despite not having the set-up praised in this thread I still think with my tweaking and no chance of natural gas (cheaper than propane by about 15% here last time I looked) I'm doing pretty good. Can anybody add advice to help me more? I would but on ODR, but I don't think it would do much more than I do myself.

    I am doing a complete change of hydronic heating souces/control in a building at the NJ shore with a contractor. It will be interesting and I mentioned it about nine months ago. We'll be ripping out an old W/M 4-section oil boiler, and installing two small Mod/Cons (there's natural gas there), and it's nearly all basboard heat. I'll give an update soon.

    Thanks, PJO
  • Brad White
    Brad White Member Posts: 2,398
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    You pretty much nailed it, Andrew

    with your comment about the time the flue gasses spend in the heat exchanger. That "residence time" or "retention time" is key, plus at a lower firing rate (lower mass flow), it is coming up against an exchanger surface area designed for up to four times the combustion rate. It naturally figures that a lower firing rate, say 25%, takes four times as long to pass through.

    The principle applies to any heat exchanger but has to be taken among other variables. It is an "all other things being equal" comparison.

    In the big scheme of things, that low velocity, if not turbulent, can also "hurt the cause" because of laminar flow, but the typical 4:1 turndown is reasonable.

    Even if you had 25:1 turndown, you are still burning less fuel, to illustrate the extreme. It is all good.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • carol_3
    carol_3 Member Posts: 397
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    On the topic of setback stats, what about comfort?!! How are we to sleep under those mountains of "luxurious" down comforters, engulfed in the folds of the pillow-top mattress, if we don't setback the heat at night? :)
  • Unknown
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    Ironically, you'll pay extra for that luxury.

    Noel
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    In the nude with neither, one or both feet protruding depending on your degree of spooning and the weather outside...

    No "pillow top" but I'll confess that I do enjoy "luxurious" bedding and there's never been a problem at maintained 65F-67F.
  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
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    Fire OFF - Don't turn your back on a draught sucking flue

    Thanks Ron for neat comparative numbers. I want to chop up the 10% difference a bit further in an attempt to sort out what might be gained on condensing and what might be otherwise lost to the flue.

    This I think is a difference worth considering in your two setups. Look up the flue. I know we are all guilty of obsessing about combustion efficiency numbers... and we casually forget to consider what happens in between when the fire is out.

    Live chimneys made of solid rock provide natural draught we inexpensively pay for with a bit of heat.

    Modern forced flue arrangements provide solid draught we inexpensively pay for with a bit of electricity.

    Nothing is ever free. If we'd run both smoke handling devices continuously we'd probably see not much cost difference, if anything at all, the natural flue should be cheaper to operate. This is mostly marginal. However we don't run household boilers continuously throughout the winter (except for the people of this original study...) and this adds a big difference to flue operation. Natural chimneys though efficient at doing what they do, they can never stop themselves. Too much of a good thing quickly turns into a nightmare, chimneys never stop sucking and when the fire is out, they still suck and they keep sniffing up what can be a huge heat loss. Flue dampers help but they are not flue seals either, there is leakage.

    Forced electric smoke disposal has the huge advantage that we turn it off at the command of a control module.

    These differences are applicable to any system, air, water, steam, they always provide a benefit but no where so big as in hot water applications. What is there to suck?

    Without meaning any disparagement towards hot water - because this is a problem that stems from system design - unlike steam and air, the liquid heating fluid does not know where to drop its cargo of heat once the fire is shut off. In hot water, just because of it's massive weight, there is a huge load of heat turning around in circles in the system: to water, the shut off boiler is just as good a place to cool as any other radiator in the home, the boiler is probably an even better place to chill if it is attached to an air sucking flue. The basement breeze sucked up through the boiler is ideal for cooling off the entire system, presuming basement air temperatures are lower than upstairs rooms.

    The lowest point to dump all the system heat is into the basement air sucked up into the flue. This loss happens every time an old design hot water boiler goes out on fire. There's no doubt in my mind that under the worse conditions these losses can be enormous and well beyond anything labels will tell us.

    Preventing short cycling minimizes the loss. Primary secondary piping stop a large part of that loss, but not all, because of gravity, water will still travel wherever it pleases. Same thing about draft hoods, they help but not to the last bit. Caravans of boilers avoid loosing big chunks of heat all at once. And the ultimate today in hot water heating is the electric flue mod con machine.

    Just to put numbers I'm guessing at on Ron's percentages, I would believe studies telling us his observed 10% difference between the electric flue mod con and atmospheric duo to account for one third to the flue condensate squeeze and for two thirds to the off cycle flue cooling losses. What do you think? It's easy to measure, collect the flue juice and give yourself about a 1000 BTU bonus per pound - stack it up against boiler 100 to 80 input output relation and see how good it is.

    Sources for inefficiencies in hot water heating are numerous. Without listing them all I would link the big ones to system inertia, general overheating of the premises, low temperature inefficiencies, off cycle flue losses, under-radiation problems, fire cycle flue losses, mixing losses, pumping efforts, losses to uninsulated pipes, pilot ignition, blah blah blah... in about that order of decreasing importance, all stuff the yellow labels don't tell us much about.

    I think with poor system design, there is lots of opportunities to go very wrong on any hot water system. This also makes it all that much a good reason to get things right in the first place and once you get all the wrinkles out, the uniform smoothness of hot water heat is probably impossible to achieve with any other heating method. This doesn't mean either that it is cheaper or more efficient by default.

    I think Archimedes lounged around in a hot tub a lot. We could also all just huddle under Carol's luxurious down comforter. I'm there already.
  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    Carol...

    I'm with you....my statements only apply to a baseboard or panel-rad application, using a Mod-Con. I too like to sleep in a "cooler" room. There are many "smart" t-stats
    and control systems that setback works great! -Gpex
  • Unknown
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    How about just not setting it back up in the morning?

    Keep a warm closet/bath, cool bedroom. You'll spend most of the time in those two warmer areas anyway.

    If you stay in the bedroom... well... think of another way to get warm ;)
  • scott markle_2
    scott markle_2 Member Posts: 611
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    laminar flow

    Brad when you speak of laminar flow I assume you are talking about water not flue gas?,laminar flow describes the condition where by the outer layers(ones in contact with pipe wall) move slower than the rest of the flow,Correct?

    Most systems will have a boiler flow rate that is not necessarily linked to firing rate. I would love see smart pumps that operate in concert with mod-cons in this way. Although I'm not sure of the how the control logic actually functions, the vito 200 does this to some extent with it's packaged vario-circ.

    From the all things being equal perspective it could be inferred from the chart that oversizing would have a positive effect on efficiency, as the boiler would be running at the lower end more of the time.

    The 24k Vito in my low energy house is an example. Because of short cycle (or pulse mode as some prefer to call it) I opted to confine the output of the boiler to it's lowest setting (blue potentiometer on the back of main board). This helped a bit, I will probably remove low loss header this coming season as suggested by Canadian Tec. to further address this

    Basically I've taken the mod out of the con. Fuel consumption has been very impressive.Makes me wonder if a properly sized NON- modulating condensing boiler which has this ideal ratio of hx to flame may not be a viable approach.Provided there is a buffer tank and control system which would prevent short cycling.

  • Brad White
    Brad White Member Posts: 2,398
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    Both flue gas and water, Scott

    Laminar flow can occur in any fluid be it a gas or liquid. Same principle.

    I agree a higher constant flow rate would not have that issue but the Vitodens heat exchanger, a rectangularly configured spiral tube, would have enough turbulence inherently to allow low water flow rates with superior "wiping action" and no laminar layer to speak of.

    But in the case of my post, I meant flue gas and at that it was more academic than practical. There is enough swirling in most burners and especially the Vitodens as we are discussing, to make laminar flue gas flow a moot point. Those sequenced gaps in the HX see to that! The fact that the Vito 200 can modulate flow with firing rate is a double benefit, IMHO.

    Your points about a buffer tank are well taken if non-modulating. I will have to look into what you said about down-firing if possible. (My Susan's Vito is still double the heat loss but heats domestic HW "a little too well" if you know what I mean. Bathtubs can now be filled to over-flowing by those too young to pay for the privilege. :)
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
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    Yah..but the point was

    BB works with OD reset on any type of boiler.

    The fact that a condenser is better able to take advantage of that fact than a non condenser.............that just goes without saying.

    I looked at a job in a local church Saturday that contains a huge fan coil for the sanctuary, some CI rads, some commercial type fin convector cabinets with fans, some BB and some large finned convector type cabinets. The current CI SlantFin is leaking like a sieve. Guess why??

    There are a host of other problems with the system related to the PONPC, pumping capacity of around 250GPM when it needs only 40-45, gravity flow checks installed sideways, air problems galore.........but!!

    The boiler I recommended is modulating and condensing. There is no other rational choice. Their fuel bills are $1,200 per month year 'round on the budget plan. I told them they could plan on a minimum savings of 30% and probably as much as 40-45%.

    The building committee guy and the maint guy about fell over when I showed them the size of the boiler compared to the old beastie.
  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
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    'nuther way to slice it.............

    > I know only what is shown in that diagram, and

    > that Viessmann provides more engineering data

    > than any other manufacturer I have seen.

    > Therefore I assume other manufacturers have not

    > bothered to publish this data for their

    > customers. I assume this is a mod/con phenomenon

    > rather than just a Vitodens 200 phenomenon, but I

    > have no proof. It seems like efficiency

    > increases in the condensing range must be due to

    > flue gas condensation, which should be

    > independent of the exact boiler model. I'm sure

    > other boilers would not track those curves

    > exactly, but they possibly would have very

    > similar curves of their own.

    >

    > If anyone has

    > more information, I would be very interested.



This discussion has been closed.