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flow vs. head in multi zones

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Thanks for your thoughts. What were the systems that you have had good success using the 15-58 for the boiler side pump? As stated earlier, I don't have the luxury of a low temp radiant system to shed btu's. This is fin tube baseboard and while the delta t approaches 30 degrees at design, under MOST conditions, it is much less. As such, with a slim temp rise, I can envision the boiler bouncing off of high limit.

By the way, I did enjoy your video installation of the Knight a few weeks ago!

Larry
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Comments

  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    how does this work?

    I know that head is determined by the longest run in a multi zone system, but what happens to flow when 1, 2, or 3 zones are calling? Does the circ move more gpm or what? And then there is the whole velocity thing. As I get closer to swapping out the old boiler for a Knight with P/S piping, I'd like to get a feel for how the boiler may/should react to varying loads and flows.

    I appreciate all your help with this.

    Larry


  • Load on the boiler is the load of whatever is calling at the time.

    From a flow perspective, when less zones are operating, the open zones get more flow, but total flow is less frictional losses elevate quickly as velocity increases. So if you only had one zone operating, it is getting a lot more flow than the zone really needs, but overall the pump is still pushing less flow than it would with two zones open.

    You balance the system in an "all calling" situation. Then as zones turn off, you have more than your minimum flow in each zone.

    A pressure bypass valve may be needed to keep velocity down when your small zone is calling (if you have one). If you figure out whether the pump you're running will have too much velocity going through the smallest zone, if it's the only one firing, you need a pressure bypass valve.
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    Rob

    Thanks for the info. My system is remarkably simple with 3 baseboard zones and an indirect with its own pump. Currently the 007 has serviced all zones with ease. The new setup will have a 15-58 for the zones and a 26-99 for the boiler loop. I am anxious to see how the system will operate with the 15-58 at speed 1 vs. speed 2. (the 007 is the same as speed 2) Lower speed should give me a higher delta t across the system, but I have not yet figured out what that will result in for what the boiler sees as return temps considering excess flow from the boiler loop. (does that make sense?) Higher return temps in the boiler loop would decrease the delta t at the HX and if I have a correct understanding of how it works, should keep the burner at a lower input, hopefully still condensing much of the time.

    Thanks,

    Larry


  • Condensing is based on temperature, not output. YOu can be at 100% output, but at 120 degree SWT and be condensing. Or you can be a 50% output, at 160 degree return and not be condensing. It's easy to confuse the two but do not confuse temperature and output. You will be using outdoor reset, right? Not modulating to a setpoint temperature?

    You want return temperature as low as you can get it. Without a buffer tank, you might not have a lot you can do there, but outdoor reset helps. A smaller pump on the boiler might help as well, as in an ideal world your BTU train would have to run out through the emitter before returning to the boiler, though that's not always feasible.
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    I've got the condensing part

    as in temp not output. Yes I do and will have outdoor reset. And no there are no plans for a buffer tank, so I am aware of the limitations in that area. I would love to have a smaller boiler pump but the 26-99 is apparently required to prevent hi limit shut downs from low flow through the HX. Perhaps I implied more importance on condensing then modulating, but I suspect that overall energy efficiency will be from modulation more than condensing. I am removing a cast iron 133k input, 109k output with a Knight 80. My heat loss (SlantFin) is under 60k at design of -20. The emitters at about 120 feet total should be around 70k potential output (if I figured that corrrectly).

    Again, thanks for taking the time.

    Larry


  • Modulation is smarter than you, unless you have mass in the system (buffer capacity). Either you emit the BTU, or you don't, if you don't, it goes back to the boiler, effecting the apparent load on the boiler. Turn up flow in the secondary and return temps rise. Turn down flow in the secondary, and the boiler returns more of its own supply water, raising return temps. Unless you are in a situation where you can ditch P/S, that's the name of the game and you can't cheat physics ;)

    the mod cons do have significant pressure drops across the HX coil, so bigger pumps there are common. I still hate to see them! I'm getting used to UP15-58's pushing 6k Sq Ft houses with no help... to turn around and put in a 26-99 for the ten feet around and in the boiler ticks me off!!

    But, I'm a weirdo like that. Best of luck Larry! Have fun playing with the system.

  • hot_rod
    hot_rod Member Posts: 22,158
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    Boiler pump and system pump

    You might consider a ECM delta p circ for your system side circ. Maybe a Wilo or Alpha, or the new Laing. This pump would replace the need, if there is one, for a pressure bypass valve. All a bypass valve does is shed some head, so to speak. I don't consider PAB's until I have 5 or more ZVs. With the ECM circs the pump adjust it's output as zones open and close, and they use about 40% less energy doing it!

    The B&G 100 was such a stellar circ for zone valve systems as it had a very flat curve. I don't know that any of the current wet rotor circs match that curve exactly?

    I'd like to see the same ECM circ used as boiler pumps on mod cons. Set up to watch a delta T and adjust flow accordingly. Actually I believe the Viessmann Vitoden 200 has a ECM boiler circ.

    Now you have two smart circs that learn your system curves, and use the very least amount energy possible doing the deed.

    Exciting times in the fluid handling industry.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream


  • What does zone valve count have to do with it?

    if you have system pump X, it doesn't care if you have two or ten zone valves. If the smallest zone is too small to take the flow from that pump, you need to bypass. Unless you go bleeding edge with the delta-p pumps most of us still can't even get pricing on yet ;)
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    circ sizing

    Rob, I'm with you on the distaste for larger pumps for the sake of the hx. Up until recently the 15-58 was just fine for boiler pump on the 80M. I can be happy watching my gas usage drop, but that loss of efficiency on the electric side bums me out too!

    Larry
  • hot_rod
    hot_rod Member Posts: 22,158
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    In my systems

    I rarely need more than a 1/25 hp circ to "get the job done.". When you lay a system curve over the pump curve, or use Siggy's simulator software you'll be able to plot that circ with the various zone valves open and closed. Even with one small zone, rarely would you have a velocity or noise issue with a small flat curve 70W circ.

    Now if you install micro tube high head circ, systems you need to pay more attention to where you are running on the curve as zones close.

    It's actually the mix of ZV and circulator that you need to look at to make the best choice of PAB or not. Not just the number of ZV's as you correctly stated.

    Pressure activated valves really just treat the symptom, not the problem, which until now has been the inability of the circ to change it's mind and adapt.

    Still one circ running a bit off curve at certain zoned conditions is still a lot better then a wall covered with identical circs ALL running way off the knee of the curve. And consuming 1000W of electrical power while the are at it. (unless you're a pump salesman)

    Sorry about your hassles getting ECM circ pricing. Have you spoken with Mark Hunt? He's in that loop :)

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • tim smith
    tim smith Member Posts: 2,752
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    ?? good time to consider a Wilo Stratos

    Larry, this is one thin I think the stratos is well suited for. depending on how micro zoned you are, the velocity may be too high and the bypass sometimes is not the ideal solution. Just a thought.
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    Tim

    I had that thought the first time I saw the info here on the Wall. The whole concept makes a lot of sense to me. In my situation the 3 zones are fairly similarly sized and we have lived OK without a bypass for many years. (but I have enough time to look into it)

    As Hot Rod noted, using one for the boiler pump would be really neat as is the case with the Vitodens. Perhaps the next generation Knights and other mod cons will get the pump and boiler to talk to each other. Until the the factory blesses the use of delta t pumps for boiler pumps, I'll be watching my electric meter spin.

    Thanks for the thought.

    Larry
  • Weezbo
    Weezbo Member Posts: 6,232
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    Good Morning.*~/:)

    Once again you have spun the rap so straight it stung :)

    Touche budd ay. :)

    i have been going round around on how to deal with flow if or when i do ever get the piece to bolt on my oil fired boilers...

    i had a bit of a revelation so thanks to You again.
  • Stratos on Multiple Zone Systems

    Good afternoon guys. Steve Thompson here, VP of Tech and Trainig for WILO.

    Yes, this is one of the applications the Stratos is exactly suited for. It lowers it's head automatically as the zones close down (and of course increases it's head as zones open up). Makes sence, less BTU requirement means less pounds of water (flow) and less head loss.

    Not only does it save a pile of electrical energy it also totally eliminates the need for the pressure bypass, the requirement to wire from electric zone valves to the pump (it deadheads at extremely low speed and low wattage hence can stay running during very low and no flow conditions), eliminates high velocity noise that sometimes occurs with one zone calling and stops the high pressure the last zone valve has to close against. Self contained with no external sensors to install and extremely simple to set up (one page start-up manual).

    Appologies for the sales pitch but it is truly an amazing product.

    It is in stock in USA and Canada (tried and proven in Europe for 7 years!). Let me know if you require additional information or documentation (there is some on Dan's "Green" page).
  • scott markle_2
    scott markle_2 Member Posts: 611
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    Flow rates and P.S

    One of the pitfalls of primary secondary piping and condensing boilers is the loss of high delta T's that results when primary flow rates exceed secondary.

    I recently did a boiler replacement in a small two story structure. The open floor plan and (generous)almost full perimeter base radiation seemed ideal for a medium temp high delta mod-con conversion. In order to achieve the highest possible delta-t I opted to create a very long single loop that would include both floors. To provide separate control of the upstairs base while preserving this long loop I devised a piping arrangement that utilized a differential bypass valve that would induce flow through the upstairs base and then through the downstairs. When upstairs temp was satisfied a remote mounted trv would throttle or stop flow, in this case the flow would bypass the upstairs base and flow through the downstairs loop via the DBV. (See piping schematic.)

    At any rate I thought this was fairly clever and it worked quite well with one unforeseen flaw. The system flow ended up being lower than the boiler flow rate even with the 15-58 equipped gb boiler pump on low. The gb allows max. burner output settings. I adjusted this at what I estimated my secondary flow rate could actually move(in btu's).Figuring this would provide some added protection against low boiler flow rates. Ultimately with all this effort at creating a highly efficient conversion I was foiled by the flow mixing that resulted at the P.S. T's. My cool retun water was somewhat warmed by bioler supply water as a result of boiler flows being higher than system flows.

    I considered a smaller boiler circ. but I'm pretty sure Budarus would not give this there blessing. So opted to forgo highest efficiency in favor of compliance with manufactures recommendations.

    Any thoughts on this?
  • Min flow rates

    Great point Scott.

    As with most hydronics it is probably a "it depends" answer.

    If it's a primary/secondary system using circs the primary is likely constant circulation anyway (typically not a smart pump application that would not achieve the best payback). Temp differential or temp setpoint circs might be an alternative.

    If the secondarys are valved they could/should be wired back to the boiler. No call for heat, no fire (although the boiler firing rate would have gone down by that time possibly causing more zones to open - sounds like we're moving towards continuous circulation, only providing enough heat to satisfy each zone). Will the system get confused? Not likely, these series of events take a while to occur.

    If there is a low flow problem with the boiler the Stratos can be set on constant pressure, not variable pressure (increasing it's lower flow head setpoints that would help solve the low flow issue). The Stratos also has a built in temp sensor that use the system water temp to influence the head setpoint.

    Another "it depends" is on multiple boiler projects the boilers could have "shunt" pumps (small, constant speed circs dedicated to the boiler flow).

    Via our OEM devision we are in communication with the boiler people to see how this will affect their boilers.

    The new age of hydronics is amazing isn't it - lots to consider.
  • scott markle_2
    scott markle_2 Member Posts: 611
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    stratos

    Steve, would you kindly provide me a link to more comprehensive wilo stratos and eco literature (pdf. files)

    I don't believe the cd that I recieved in Albany included this this material(and I recall Mention of a lengthy installation guide.)

    Honestly while I was supplied with reams of pump literature the Eco and Stratos are the only willo products I would likely be seeking out. And of the two the eco is more likely to fit with the sort of low load systems that particularly interest me.

    the vitodens 200 comes with a variable speed boiler pump (basically size equivalent of a 15-58) and the ability to set high and low end speeds. By comparison,in my estimation, it seems we are being asked to over pump boilers such as the knight and others at least in terms of the amount of actual energy that is being moved, (the high delta we want moves more heat with less flow.)

    I know some of the reasons for this (steam flash off nuisance shut downs,zoning flow variations etc.), and perhaps reliability is ultimately more important than efficiency. But Remember that the electricity use issue that the original poster laments may be less significant than the condensing efficiency lost to primary secondary mixing that dilutes high delta return temps.
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    Steve

    Thanks for your input in this discussion. Could you tell me which Wilo pump would be considered direct replacements for the Grundfos 15-58 and the 26-99.

    Also, what sort of electrical draw is likely for these at about 10 ft of head for the 15-58 equivalent and the 26-99 at about 24 ft of head? While I don't want to seem like I'm stuck on electrical usage verses the other benefits of these pumps, achieving as high an overall efficiency as possible has been one of my goals for this install.

    Thanks for all the good information.

    Larry
  • scott markle_2
    scott markle_2 Member Posts: 611
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    P.S

    Larry,

    I'm repeating my self,hoping that someone will either refute or confirm my assertion.

    loss of condensing efficiency by boiler flow being higher than system flow is likely to effect overall efficiency more than pumping costs issues.

    I really don't understand why such a large circ. is being recommended on the boiler side. Have you calculated what the actual the flows will be on each side based on the selected circs. (all valves open)?

    If highest efficiency is your objective then I would question the use of a boiler that requires flow rates that may exceed your system flow rates under all conditions. Which(just guessing)seems like what the circ. pairing that you describe may produce. It's my opinion that P.S arrangements involving mod-cons should be designed for higher secondary flow rates under most operating conditions,right? we don't want tempered return we want return as cool as possible.

    Yes lowering the speed of your 15-58 will raise system delta, but may actually do the opposite for the boiler as a result of mixing.
  • Weezbo
    Weezbo Member Posts: 6,232
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    Larry.

    Here is one of the links that is very cool out of England.


    May Take a while buh this is a good read .from back when we were discussing the topic of variable flow variable speed constant flow circulation and modulating condensing boilers..a couple years ago... i wish i still had my book marks from before the computer crash ..

    different day different dollar....

    Another one of our aspects ,within that discussion went along with the idea of flow reversal into radiant heated concrete slabs..which though directional flow changes ,one may deliver Btu's creatively to an area. to me , this particular strategy is one that may be used with a variety of emitters and imposed loads....what i am getting at here is the loading of thermal mass from a source with variable flow constant circulation does not have to do what its been doing it can do what we design it to do... sure ,it may be a means to get heat into the thermal mass of a slab as a fix to overly long loop lengths,buh, depending upon the design of the system the same strategy may be employed to produce results that are not part of a Problem that cannot be corrected with another amazing creation....The Eraser ...

    The Sedbuk.ratings, Archie Kidd Boilers, the boilersim link WWW.boilerinfo.org, are like mini windows into the information on various condensing modulation system control venting ...

    been dinging around slugging coffee this morning ,..thinking.... Oh O! *~/:)

    when modulating condensing boilers fire the fan speed changes somewhat like what our computers do everyday when its doing the daily whatever its doing to purge the system:)

    not all condensing boilers design happen to require tremendous amounts of flow at every condition within its firing range ,that was recognised quite some time ago...just why those designs are not what are moving the industry forward i don't know....move mountain move ...:) an old Chinese guy and his wife lived on a hill overlooking many plateaus ,mountains and valleys and one gert mountain stood in the way of a wonderful view of the ocean, so he went about removing it one rock at a time after a while he enlisted his small children they grew up and they too continued to remove the mountain then their children began to turn a hand at it..so What ? it just shows that mountains can be moved with determination and faith and indeed it will change our perspective...

    Check out this appliance, Heritage Uno. avec boiler attachment ....
    well civilization will catch up to us one day and lo and behold that which is old shall become new *~/:)


  • You emit the BTU, or you do not.

    I personally don't really think flow comparisons between primary and secondary mean squat. Energy is conserved; either it is emitted, or it goes back to the boiler. If you have lower flow coming back from the secondary circuit, it's dT is larger, and it will mix at the PS piping connection, with a certain impact on the boiler return temp.

    If you have higher flow coming back, the dT is smaller to begin with and again it mixes at the PS, and it should have exactly the same effect on the boiler return temp. You can't fool physics, IMO.

    Either you are high flow, smaller dT or low flow, larger dT. Those are the choices. low flow, larger dT is more efficient in distribution and in heat transfer, so that's what we design for when possible.

    The lower limit to flow here is how low a flow through the boiler will extract the output you need, without heating the boiler up so fast it trips high limit and cycles off?

    That is the $64,000 question that is ignored, and would vary for each boiler design. That is one advantage of the Viessmann system, since the controller can see boiler internal temperature as well as control the flow rate through the boiler, so no matter what system it's connected to it can vary its operating characteristics to match, controlling flow as well as temperature.

    In short though unless you can do that, I think it's fairly moot where the higher flow is once you get beyond startup conditions. That's an important consideration of course (startup condition behaviour)... and that may dictate the need for a buffer tank. But if return water would overheat the boiler, so would just slowing down the boiler pump.
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    You can't fool physics

    Rob, thanks for your continued perspectives. As has been illustrated by both Scott and you the limitations that are inherent to P/S piping, there are very few seemingly perfect systems when dealing with boiler replacements, and trade offs will occur.

    The Vitodens has an advantage to be able to vary boiler flow and effectively deal with that where the Knight does not. In my situation, I believe that the Knight will provide significant improvements to both efficiency and comfort compared to what it is replacing.

    This has been a good exercise to determine what flows will be in both system and boiler loops. (The B&G System Syzer is a great little tool) I will be very interested to see how responsive this new system will be by throttling down the output as delta t decreases across the HX (if in fact this will happen). Also, my hunch is that condensing will still take place much of the season with the outdoor reset in use.

    Now if I can make good use of those highly efficient pumps……………

    Larry
  • Ron Schroeder
    Ron Schroeder Member Posts: 998
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    General rule of thumb #1

    The boiler is probably too big.

    General rule of thumb #2

    The circ. is probably too big.

    I find these to be true at least 90% of the time. ;-)




    Seriously, you do need to run the pump curves.

    I had 15 zones on a single Grundfos 15-58 set on low with a pressure bypass valve.

    It's now running on a 15 watt Laing ECM circ.
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    interesting stuff

    Thanks Weezbo for that paper. I will give it a good looking at very soon.

    Hope all is well with you and the upcoming season is a good one.

    Larry
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    Ron

    What can I do? The factory wants to have a 26-99 on the boiler loop and even supply it. Apparenty there have been enough high limit trips and whatever that this is their fix. I do believe that a 15-58 on low speed would work just fine for the system loop, but as far as the boiler loop goes, if the factory says it needs to be a 26-99 and I do something else, that puts me in a very precarious position. Thanks for your thoughts.

    Larry
  • Ron Schroeder
    Ron Schroeder Member Posts: 998
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    Hi Larry,

    The smallest Stratos is similar to the 15-58 and it draws from 9 to 85 watts depending on flow.

    When you figure out your primary loop if you are including the boiler in the primary loop rather than on it's own secondary, don't forger the head loss of the boiler heat exchanger in sizing your primary circ.

    By the way, I figured that If I had zoned my own house with 007s, if they were all on, the heat from the circs. would just about equal the structure's heat loss. ;-(
  • hot_rod
    hot_rod Member Posts: 22,158
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    Low loss headers or hydro-separators

    seem to be a better match for mod cons as opposed to PS piping, per say.

    My testing shows a lot less "blending" goes on in the larger chamber then in a closely spaced tees, P/S. Even with a higher head boiler circ and a low head system circ.

    I'm not happy about needing a high head circ for the Knight either. Memories of early copper tube boiler headaches :)

    I do have a bunch of 80 and 105 Knights running fine with the 15-58.

    One place to watch is when the kick out of DHW or any high temperature run cycle. You need to have the post purge cycle set long enough to purge all the residual heat from the HX or they can over-temp and kick the high limit.

    On the plus side they do auto reset, but if you connect your laptop and view the run history you will see high limit faults.

    To the un-trained ear they sound a lot like the boiler is satisifing it's call.

    I'll keep saying it also...I think poor water quality may be coating these small HXers and causing the flow/ over temperature concerns. Just as they did in the "limed up" copper tube days.

    Perhaps the manufacturers are using that velocity increase offered by a high head circ to scour the HX surfaces. But with poor water quality that higher velocity could lead to an erosion issue perhaps??

    I've had this exact same issue with reverse indirect tanks with hard water and low DHW side flows. The coils lime shut!

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • scott markle_2
    scott markle_2 Member Posts: 611
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    conservation of energy

    Rob, it's helpful to get others perspectives in order to fully understand these relationships,thanks for contributing

    Delta and flow determine energy transfer in an inverse relationship. High delta/low flow is equivalent to High flow/low delta. This relationship has always confused me a bit. For example, from the perspective of the emitter, say a long radiant floor loop, a lower delta across that loop can move more heat to the room because of it's higher overall temperature.

    If we have a high heat loss area (in radiant application) we will design for a low delta in this area by ensuring higher flow, right?. This suggests to me that the inverse relationship between flow and delta is not exactly linear. In the radiant situation described we can move more energy with high flow/low delta than high delta/low flow. Correct?

    Not so sure that the conservation of energy law encompasses the point I'm trying to make about primary secondary flow rates. If primary(flow) is greater than secondary flow mixing will occur at de-coupler. Secondary return will mix with primary Supply. The advantageous high delta of our sytem flow is diluted.

    Wouldn't it be better if the boiler flow was matched to system flow thus preserving the high delta of the secondary loop. While warm water returned to the boiler is not lost(conservation of energy) an opportunity for best latent(condensing)heat recovery is.


  • flow rate and output relationships are not linear.

    However, flow rate and mass flow, or heating capacity carried within the water is linear. Double your flow rate and you carry 2x BTUs from point A to point B if you don't lose more heat along the way. Now you may not emit twice as many BTUs from the pipe, because you've only increased your average temperature by half of your differential temperature. But you can CARRY twice the BTUs, and as such, if they are not emitted they have to come back to the PS tees. Perhaps you emitted a little bit more if you cranked up the flow, but ultimately that part can't change too much.. unless you add a buffer, you are limited to emitting what the load can take at any one time. You don't get to "fake that out". Increase flow to get more heat out of the boiler faster, and the zone will just shut down earlier, and make you run in part load conditions more often.

    In the end, I'm not sure it matters how the flows match up if they are hydraulicly separated. Either you mix a little boiler temp water into a colder return (boiler high flow, radiant low) or you have more warmer return water (low boiler flow, high radiant) UNLESS you can intelligently manage pump speed through the boiler to optimize differential across the boiler and power usage.

    I might be wrong... but that's my hunch.
  • scott markle_2
    scott markle_2 Member Posts: 611
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    more energy movment thoughts

    Rob, thanks again for your input. The point that "you are limited to emitting what the load can take at any one time." is helpful,as is the distinction between capacity and delivery.

    A gallon of water has no fixed energy content, it has a carrying capacity, but not a fixed energy content. It's energy content is the degree to which it's temperature is different from it's environment.As in 80 water carries no energy in an 80 deg environment

    As far as the question- "Does primary exceeding secondary have an adverse effect". I have measured this and in the system I described above(any comments on that schematic?) .

    I get what your saying about the load ultimately determining how much energy moves. My observation of this diluted system delta,(real and measurable by simply "feeling" the pipes) was made during a demand for heat,not when the system had been running for a long time and had reached a constant circulation btu line/load equilibrium. But in reality how often does a boiler run in perfect equilibrium with load. Most systems run in excess of load and use t-stats. Even smart constant circulation systems will experience user adjustments and setback. And for most of the season min- modulation exceeds load. So while I'm having a though time with the phisics, my intuition (and what I remember from viessman low-loss header literature) Tell me that with hydraulic de-couple secondary should be greater than or equal to primary, for the majority of operating conditions, if optimal boiler performance is desired.
  • Ron Schroeder
    Ron Schroeder Member Posts: 998
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    If the hydraulic de-couple is a 4 port buffer tank like this:

    http://www.heat-flo.com/Products/Buffer_Tanks/buffer_tanks.html

    the secondary flow can even be micro loads.

    Personally, I'm a huge fan of using a 4 port buffer tank as a hydraulic de-couple. Even better if the buffer tank is a reverse indirect.
  • hot_rod
    hot_rod Member Posts: 22,158
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    The one drawback of a reverse indirect as a buffer

    is you have to run it up to 180 or so to get much DHW performance. So then your heat loss from those poorly insulated tanks goes up, and you have to mix down for any radiant temperatures. So some heat exchange losses again.

    My idea is to let the buffer run at design temperature of the load, or even modulate it on OD reset. Then use a small low capacity flash tank or plate HX to bring the DHW up to use-able temperatures. Gets to be an expensive compulation, however.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream


  • I"m with HR here.

    Scott, as to what you were saying, under startup conditions if the boiler flow is too high and the secondary flow too low, one thing that can happen is you don't even get the full capacity of the water in the system to absorb heat. If it goes back TOO FAST to the boiler, it can trip itself out on high limit before you even finish heating up the loop.

    That's definitely buffer tank territory, IMHO. Somewhat more up front cost, but not necessarily a whole lot (the boiler buddy siggy turned me on to is very reasonably priced) and it means you don't have to jack up pump size or electrical usage on the radiant side.
  • scott markle_2
    scott markle_2 Member Posts: 611
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    buffer

    Thanks for the link Ron.

    Is a reverse indirect the boiler is piped to the tank and the system piped to the coil? and a separate indirect used for dhw?

    Seems to me that the issue of sizing for low load structures, really comes down to DHW requirements. Most people want to save energy but they are not willing to give up a steady 2 gpm flow of hot water. To supply this we need 75k or so. So in low load structures we are really sizing for DHW. This is probably why mico mod-cons are not being made

    Heres an idea,what about a buffer tank with a variable differential based on OD temp. As it gets warmer outside the low end (kick-in) is dropped widening this differential. The system side would run independent of the boiler using a mix valve and ODR. The boiler would run based on demand from the buffer tank, it's max (heating) firing rate(if adjustable)would be set at the highest anticipated load for structure. Perhaps some sort of S.R delta logic could also be applied to optimize firing rate for above min-modulation conditions.

    The problem is creating a demand which is great enough (when it doesn't exist) to give high condensing efficiency without short cycle, or the 8 second vitodens style "injection" burns.
  • Mitch_4
    Mitch_4 Member Posts: 955
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    Why I try to avoid wall hungs

    high pressure drops. While the Dunkirk has a limited option, I regularly use the fixed input units because of the low head requirements.

    Would love to see a wall hung low press drop unit. or dunkirk make a lower range unit.

    Mitch
  • scott markle_2
    scott markle_2 Member Posts: 611
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    not that bad

    I'm getting a bit carried away, the system in question works great, by it's simple design system flows are consistent whether both zones are operating or not, my system delta is very high and I am not a using differential bypass in a way that dilutes my return delta.

    While my boiler flow did come out higher than my system flow as evidenced by somewhat warmer boiler return than system return, these flows are not nearly imbalanced enough to create the problem you describe. However as a precaution I have the gb's (heating)firing rate capped at 45K. Wish this setting was a bit more locked-out (like the potentiometer on the vito LGM)

    I'm fairly confident (and if it was my house I would do it) that I could put a smaller circulator on the boiler and get the full benefit of my low system delta at all times.

    I'm being obsessive and impractical, I just love the whole squeezing out latent energy thing.
  • hot_rod
    hot_rod Member Posts: 22,158
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    Buffers are still a stop gap means

    until something better comes along.

    The very best place to store you energy until it is needed is in the fuel. Gas, Lp oil, electricity, etc. Once you combust and change from chemical to thermal energy a portion slips away. Efficiency loss in the combustion process, pumping, insulating, and re pumping when and where need all "cost" you.

    A 1 btu/hr to 50,000 btu/hr modulating condensing heater is what I really reallly want :)

    Is that too much to ask?

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream


  • Seriously! 50 to 1 might be crazy though. How about crazy cheap, easily stagable series of 1k to 5k burners? Modular of course, so you can add burner or remove it easily.
  • Stratos Information

    Scott, can you please send me your E Mail information. I will send you all current Stratos information available.

    My E Mail address is steve.thompson@wilo-na.com

    Thanks.
  • Ron Schroeder
    Ron Schroeder Member Posts: 998
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    Hi Rob,

    Where can I get info on the Boiler Buddy? So far I can only find info on the Boiler Buddy magnetic filter?

    Thanks,

    Ron
This discussion has been closed.