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Maximizing efficiency of a mod con question

Xr Member Posts: 2
I have been reading posts about maximizing condensation in all the new mod cons.  I have only installed a few of them and both were on hi mass rad systems single zones so set was easy and we saw a great delta t with those and with the ord curve condensed most of the time.  Both work great and were lochinvars piped p/s with the supplied 15-85 primary.

Last week I installed a new knight whn85 in my house.  Combined heat loss calcs came in at:  addition 16k, main 1st flr 16k, in law 12k, garage 10k, 2 basement futures have done a Heat calc yet.  55k btu not including basement, and a possible future hx for a hot tub...a bit of a dream...may not happen.  So I chose a 85 based on the above....the 55 seemed too tight for any of the possible futures.  

I figured on radiant from go but after getting pricing...there is no way I can swing the costs right now.

Due to costs I chose slant fin 30 oversized for lower temps.  this was figured with sf chart using 260 for a multiplier.  

47 ft in addition (running)...really sized for 140 due to limited wall space....but it is it's own zone and the house is an open floor plan so I plan to do 130f still for the rest.  The addition would want 58 ft at 130f so I will be pushing a bit at design.  With the open floor plan the fact we rarely if ever even come close to design I think it will be fine.

53ft 1st floor,  46 ft 2nd floor in law, 20k modine in garage with sep reset curve and target of 160 or so...will tweak for lowest.  This will be on second heating zone with a sep reset curve and target.  Unfortunately if this calls when the lower temp bb calls....it will get the higher temp water.  Not a big deal as the garage heater will not be used to maintain high temps, but just to keep it above 50 when I am in the shop.  

All  bb zones are 130f target for 0 degree day.  Today it is 34f and the addition zone is the only zone running ( nothing else has been piped for the rest of the system) and the target is 116f.

My issue is this:  how hung up should I be on maximizing condensing with this set up?

I am becoming obsessed with it.  I know that this hx can handle not being piped is ps if you can maintain the minimum flows in table 6-2 in the manual.  I do not know how figure this out if someone could help me with that.  Of course with such a little load (16k) and non design loads probably have that....the boiler is short cycling a bit even at 20percent.  So I am sure I am not getting accurate first impressions but so far I have a concern on the delta tees I am getting.  Piped per lochinvar specs just like diagram on page 40 sans the indirect.  We heat hw via tankless.  

Running at the above specs I am only seeing a 3-5 degree delta tee, again just on the addition loop 47ft sf30 116 target based on ord.  When I piped this I piped a web stone purge bv between my close tees as a drain (low point).  With the system pump at speed 1 (all pumps are grundfos 15-85s) and the primary at 1 (lochinvar states to use spd2) I get the 3-5 delta t.  With speeds. Higher on either it narrows to 2-3.

Running with the ps ball valve shut....I get a solid 10 degree delta t.  

So...at this point I am seriously regretting using pumps for all zones...I woulda shoulda coulda done a vs secondary aka system pump and zone valves.  Too late now....I really don't want to change at this point all the near boiler piping is done incl. futures...wired etc.

Am I just obsessing here...?  It is overshooting target a bit sometimes so with the ps piping that means 125 out, 122 back.  Not what I had in mind designing a 130f 0degree system in the mid 30s.  This is my own house and any tweaks, gains I learn can the be passed on to my customers.  Partly why I am obsessed...I am the guy that likes....nah....needs to do the best job that I can do.  I cannot even decipher whether delta t is of great importance or not.  Excellent points have been made in both directions...ie uneven heating with large delta tees etc.  I mean if my return temps are below 130 shouldn't I be condensing regardless of the delta?  I did an experiment with the same run time with the ps open, verses shut thereby making it a push pull...with the boiler pump still running though...and with the latter and aforementioned delta of 10 I got an extra 1/3rd condensate produced for the same run time, same target.  

I am unsure at this point wether the existing boiler pump will be oversized when all the zones get going or not.  Right now it is very clear it is oversized resulting in hot supply water to go right back into the hx and lowering delta t to just 3-5 and causing less condensation.  

Wow this is a lot...sorry for a long post.  But this is we're I am at with all of this mod con stuff.  There is much information out there and depending on who you talk to different answers.

I would like to know what recommendations you mod con experts have to tweak this system.  If you think I should wait until all other zones are piped I think that may make the most sense and see how it is when there is enough demand to get above 20perc. Fire.

My thoughts:


Lochinvar states the boiler pump can be variable.  That would be awesome and I don't know why this isn't the standard.  I have looked for pumps and can't find a suitable pump or info on how to set it up


Run as push...pull and shut bv between close tees...run with boiler pump off, or remove boiler pump.


Install smaller fixed spd boiler pump


Clock bv between tees for better delta t.   A globe valve would be better.


Say the heck with it and run it....not in my nature...lol.  Wish it were....would make my life a lot easier!  Lol.  

Lastly, how much does delta t really have on condensate with such low temps. The charts that I have seen seem to indicate anything under 130 return will be in condensate mode.

Thanks all.


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    The charts that I have seen seem to indicate anything under 130 return will be in condensate mode.

    I am not qualified to respond to most of your post. But any return under 130F with a gas-fired boiler would be in condensing mode, but the lower the return temperatures, the more condensing you get. If you return water at about 130F for a typical mod-con, the boiler efficiency would be about 88% (just barely condensing). If you could run with the return water at about 80F, the boiler efficiency might be as high as 97%. So design your system to get the heat you need with the lowest possible return temperatures. I hope you will have outdoor reset on this unit so it can reduce the supply temperature as it gets warmer outside and return cooler water in warmer weather. That is where a lot of the savings will occur. Design temperatures occur only about 2.5% of the time..
  • Zman
    Zman Member Posts: 7,542

    Very nice post. You are way ahead of the game.

    Very few contractors understand most of what you have posted and even fewer care enough to chase the last couple percentages of efficiency.

    Here is an interesting read if you haven't seen it yet.


    Notice that tuning the boiler for optimal CO2 is also very important.

    In a perfect world, the boiler manufactures would design an appropriate circulator (I don't believe it exists) for your fire tube boiler and control it with variable speed. Don't hold your breath.

    Bypassing your primary secondary should work just fine. You could even slow down the secondary flows and get a wider delta t.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Gordy
    Gordy Member Posts: 9,546
    Super tuned mod/con

    Seems to be the obsession. Remember modulation is the real savings compared to a bang bang CI boiler. Getting it to condense as much as possible adds a couple of points to the efficiency.

    As for why manufacturers don't throw in a variable speed pump who knows, may be up and coming offerings gotta save some surprise for next unveiling. The big V has been for awhile now.

    Or it could be they already gave us a 40 mpg car, and we want to make it get 42. Or 350 horse, and we want to get 375 hp.

    The betterment of technology is never ending, but some things are a bit anal for the ROI, or adding complexity to the system.

    Technology is but a commodity anymore until the next great stride takes its place. Just like computers, t.v., and other electronic peripherals. What you bought this year will certainly be out dated next year or the year after.

    But in the end if it's experimenting that fulfills your need to say you did all you can then by all means do so, and share your findings.
  • SWEI
    SWEI Member Posts: 7,356
    edited November 2013
    You've put a lot of work into this

    and one of the things you've just learned is that heat loss calculations already have a generous fudge factor built into them.  Remember that the "minimum" flow rates in the manual are only required at maximum boiler output.  If your actual load is less, the boiler's maximum demand will be lower.  The other 99% of the time it will be even less.  The low head loss of that HX presents you with an interesting challenge:  finding a pump that's small enough.  Full fire needs 4.6 GPM for a 35ºF ∆T, with the HX offering about 1/3rd of one foot of head resistance.  A Taco 003B-VVF should play well with the Lochnivar controls.  I really wish B&G/Laing offered the ecocirc e-Series with 0-10V input.
  • earl burnermann
    earl burnermann Member Posts: 126
    variable speed circulators

    Here's a link to a pretty reasonable variable speed taco circulator. Set the Delta T and let her go...

    If the women don't find you handsome, they should at least find you handy!
  • bill nye_3
    bill nye_3 Member Posts: 307

    The best place for a hydronic laboratory is in one's own home. If it heating your space to the set point and you are reasonably comfortable I guess it is OK regardless of return temperature. Maybe when the other zones are running and you have more load the delta T will increase.

    But on the other hand, in our quest to condense........ the cooler the return water the more BTU value we have to add to reheat it. You wouldn't leave your windows or doors open just to cool the return water a few degrees so you could condense. And you wouldn't run a loop of pipe outdoors or through a snow bank just to get your little boiler to condense. Just be happy that you are modulating and burning way less fuel than a person with a fixed firing rate that is going to run up to high limit every time a thermostat calls for heat.
  • Rich_49
    Rich_49 Member Posts: 2,766

    the 15-85's to 008 VDTs , use the 15-85's as emergency pumps for after hours / Sunday service calls , hell they are new . You won't take a bath on several pumps that way but the VDTs will insure your Delta T on the system side at all conditions , all year .  If your system design allows you could use the Bumble Bees and see how each zone is really operating (GPMs and Watts) in real time .   And yes Delta T is important , we design for it . Keep up the search for the perfect system , you may never find it but along the way you'll find excellence . 
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Weezbo
    Weezbo Member Posts: 6,232
    Bill Nye ,

    not to start in on your first statement buh Firedragon seemed to be getting pretty good help over at BNL : ))

    Have been away for a while and have been meaning to touch bases with everyone again , Do you recall the experiment with the Hermann Boiler with the 900 psi step fired oil burner and pump ? Were the results ever published or is there a thread that was posted ,since then, with more data?

    thanks .


    *~//: )

    Did Perry and Constantine drop off the face of the Earth too ? They both seemed avid enthusiasts :)
  • Gordy
    Gordy Member Posts: 9,546
    Interesting read


    Conclusion to me is that efficiency is an ever floating percentage in a heating cycle. With a mod/con boiler.

    Depending on emitter type, you may start out at 98% and end up at 89% towards the end of a heat call. As return water temps climb as emitters warm up. Proving particularly true in low load parts of the heating season.
  • Paul48
    Paul48 Member Posts: 4,469

                 Just can't get my head around using a fixed pump on the primary, and DeltaT on the secondary. I understand the reason, and concepts of both, but keep seeing  a competition to false modulation of the boiler, that may not reflect the needs of the system. The delta-t circ essentially causing the mod con to not respond correctly to the system.

                  It seems to me, that matched flow,primary and secondary is the way to go, and DeltaT is just the product of the conditions on the secondary side.I'm just a homeowner, and enjoy learning.
  • Gordy
    Gordy Member Posts: 9,546
    edited November 2013
    Fire tube designs

    lend themselves well. Taking into account system and boiler needs for flow rates piping direct can be actually a better marriage in certain cases.
  • SWEI
    SWEI Member Posts: 7,356
    The Lochinvar controls

    have an aux output which can be configured for ∆T modulation of the boiler pump.  This pairs nicely with a Taco VVF pump, hence my suggestion above.  Turns out I got the model number wrong and the stainless version is the same price, so I'd probably choose a 003-VVST4 for this if I were keeping the primary loop.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    My Opinion On Approach

    User a buffer tank as your pri/sec, ie Low loss header. Caleffi has a Thermocon 25 Gallon and that will end your short cycling issues along side with sizing your primary or boiler pump for a larger delta, ie 35 degrees.

    Since the boiler has minimal pressure drop and a fixed speed circulator operates on its curve your best option for a boiler pump is a B&G Vario because of its ability to operate at gpm and heads lower then an Alpha, Bumblee Bee. All variable speeds pumps still operate on curves, its just a matter of how many they have and they all have limitations.

    Second I'd get rid of the zone pumps. Zoning with fixed speed pumps is no more then a recipe for over pumping. Use Taco Zone Sentry's and pick the best variable speed ecm pump for the job and call it a day.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Xr
    Xr Member Posts: 2
    Great things to think about

    Some excellent points made.

    The option of a vs boiler pump seems to suit my current line of thinking. However I now have to make time to get my 3 other zones up ASAP. I will then have a better idea of what I should do. I thought about a vs system pump and zv after the fact. Hindsight!!!

    I agree a pump on each zone is over pumping even on low. Getting 6 vs pumps and reusing these is an option, but one for down the road due to costs. Ive learned a lot in the past few days. I would have designed this way differently.

    However, with that said there is still a happy medium to everything and I do not know how much I actually have to gain by redoing everything...verses making a few smart changes. I mean all my bb zones are 130f at design. My return water even with the minimal delta t will be under 120 almost all the time. So....how much is there to gain by doing a buffer tank and/or new pumps. I may get a nice boost just by choosing the aforementioned boiler pump(s).

    That leads me to a thought I read...not sure how accurate it is: someone stated that condensation has to do with average temp of the hx....and a smaller delta will keep that lower (particularly with the lw temps I'm using). The comes the variation in bb output if I increase the system side delta too far. There is def a happy medium that must be met unless going Chris' route with a buffer and a vs system with zv. I see no compromises there. That is what I will do next time for sure, and being this is in my house I do want the ultimate set up. But i also need to get this finished...getting cold. Then there is the time and money something I am short on. Yes I will eventually be able to reuse the pumps I have so not ruling anything out yet.

    Still a bit confused on my best approach. Hopefully starting on main zone by mid week.

    Does anyone know how to figure out if I can eliminate the ps and boiler pump with this design. Use it as push pull with the existing 15-85s for each zone. My gut is saying that will be enough, but I need to quantify that with math. If this is even a good idea.

    I don't see how I'll ever get a big delta without adverse emitter performance at the end rooms....unless I do a buffer like Chris mentioned.

    Much to think about.
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