Maintaining minimum flow w/o P/S -differential bypass? bypass zone? flow switches? ideas?

keyote

I just read back over when i first brought this up with the TT, I have since come to understand a lot more about what complicates the answer minimum loads, zone size, even given temperature and flow. And am considering this lochinvar 10-1 modulator to solve some issues you pointed out, but its raised this piping through issue again my mind.
But obviously Im still a novice.And throw around terms i barely understand so please forgive.
Look I bought into the idea of green building,radiant heat, mod coms, advanced controls and ecm pumps, even solar assist eventually so im kind of fixated on going the extra mile to reduce energy, it may be the technology is simply not up to the hype yet, and ill have to accept that, already i learned that putting actuators on loops is BS and will make my zone as large as need be for the 10-1.

Attached are the non P/S details of the the two 10-1 modcoms, lochinvar is my favorite its got incredible control and explains it in fairly good detail between the manual and their training videos, I have talked to them they are adamant it can be piped w/o P/S,one of the details even deletes the extra pump for the indirect and puts it on a zone valve [see that wasnt a crazy idea]. They are also adamant they built this machine to work with variable speed pumps and there is much detail about how they integrate that into the control matrix.
My holy grail would be to combine the variable speed pumps with straight through piping configuration, which the manual is less about, However one Lochinvar employee said that it was fine as long as minimum flow was maintained. Now admittedly on 65 degree days my lowest demand manifold even with all loops on it zoned together falls below the minimum flow [at least i think it may, when i unlock the DT15 in loop cad most of my loops DTs go way way up, maybe that gets fixed with flow valves and the flows not as low as i think im clueless still.] But certainly I dont want flashing so Im assuming i could get a situation with really low flow and would want a guaranteed flow.
Both manufacturers show in their detail and I confirmed talking with them that a differential bypass is an option to assure this but I think they are imagining a fixed speed pump, I notice they also have control inputs for auxiliary flow control switch, and briefly Ill note they list half a dozen ways they also protect from low flow while also trying to prevent lockouts and cycling as well.
And oh i just remembered if im not using an variable pump I have to put a bypass between the S/R on every manifold so I would think its certainly preferable to only put in one bypass before the ZVs
I have come to understand Im not the only guy that wants this, and its just possible its arrived with this KHN machine, theres another guy at loch im going to try to talk to I wish i could speak with the engineers but thats not a done thing. I might even consider giving up zoning entirely if it would help but the house will certainly heat unevenly which perhaps could be mitigated with flow valves or something.
So i guess the question is about these ecm pumps and something along the line of a bypass thingy :] I have some ideas of why it might or might not be problematic but i wont waste time you tell me, going through the older threads of mine and others i see its been discussed.

SWEI
There are ways to make it work, even with a ΔP pump. A pressure bypass valve and/or a bypass zone can be used to ensure minimum flow.

One thing thats confusing me is looking at the curves particularly the shaded curves that denotes the pumps "variable range" im not understanding what the pump does below that shaded area. Does it refuse to run? that might be a good thing. this VT2218 i attach, which i prefer to use because im more comfortably within its variable curve with a bit of room for expansion. has language specifically about minimum flow control for boiler protection and something called integral flow check, if you dig deeper on their site they say you can adjust the variable curves band, make it higher or lower i would think that would allow a baseline speed to accommodate the boilers need, lochinvar also says they let you adjust the minimum voltage a variable speed pump that is controlled by the boiler gets, to do similar thing and they coordinate that with firing rate which can also have start rate configured . And lochinvar has ways you can let external pump control with only on off boiler command for pump.One caveate The pumps they mention are not what i am calling variable pumps ecms and i noticed just now in another thread someone differentiate between 0-10V pumps and the ecms so whats the diff besides a hundred bucks are they as efficient do the same thing?

Just for kicks imagine you solved this and you put the indirect on a zone valve [you would lose the priority pump feature but id think you could give that zone valve priority to same effect]
which leads to a question/ suggestion i had the other day, what if to solve this you make the indirect the primary loop and come off it with zone valves for CH [yes they would need a mixing valve for radiant but no big deal ] and yes you would have to be clever about indirect set points to not compromise DHW but i bet you could end up only sometimes having to fire the indirect for its own sake because CH calls going through it kept it maintained.
ONE RING TO RULE THEM ALL
I seem to recall seeing one of you at about 2 am had something like this called the tri bufferator or something

Gordy

Be aware there is a minimum flow rate at low, and high fire. The 55 has a 2.1 gpm min. At high fire. 1 gpm at low fire. So close attention needs to be paid in setup. If a single, or multiple zones call with an equivalent flow rate less than the 2.1 gpm , and the boiler goes to high fire to meet the load quicker it will lock out.

The 85 is 3.2, and 1 gpm.

Gordy

With an indirect the 55 will not make for a reasonable recovery for Dhw loads however of IIRC you are only covering one unit with the indirect. So if that size indirect can satisfy your needs without recovery I would opt for the 55. Mod /cons like to claw up hill. Your 52k by the program is less. I would not use the 85.

keyote

Gordy Thanks
By claw up hill I suppose you mean they dislike modulating down and try get back up to at least their mid range, revert to mean ? Good to know.taking the following into account would you still advise the 55 I do tend to overbuild. I attached the manual page below.
Because I was actually thinking of the 85 not 55 because you dont really lose any low end modulation or minimum flow rate at low fire, [I suspect the 55 is just a derated 85]
But you do get the extra at the high end for the indirect, but also in my case the 55 is almost exactly my load [52kbtu]and two things concern me,first is Im not convinced of my heat loss calc because my construction is non typical i had to manually compose assemblies although i tried to be acurate and conservative as you point out the panel method i devised may make it hard for btus to jump off the train, so Id like a bit of error margin, also I hope to build an addition on the roof one day that would add about 8-10 kbtu, I have capped two manifold outlets on that manifold and used 1" copper for its riser in anticipation.

You are correct It is a 50 gallon smart and though it serves a single unit, its the 3500 sf owner triplex with three baths two powder rooms a bar and a kitchen. However I suppose Id eventually add solar and that would help.

keyote

Hat
Thanks very much its explained well

"The KHN has a minimum flow requirement of 1 GPM. It also has a minimum firing rate of 8K BTUH."

"So, if you set a DT of 10 on that pump, the flow rate will NEVER be less than 1.6 GPM if the zones take the full 8K."

Taking your word as an engineer on this bit though, Ill have to think about this part and consult siggys book to understand it.
I think I can see you are subtracting delivered BTUs using the DT from produced Btus from the lowest mod of 8500,But cant figure out how you get maximum flow regardless of water temp.


"If one zone calls and can only deliver 4K, the VT is going to try to slow the flow down to .8 GPM.........which is below the minimum spec for the boiler."

which Im afraid of on 65 degree day, and Gordys worried about because of my low mass wood floors.

"HOWEVER, the capability of the pump to slow the flow down to .8 GPM is nearly non-existent unless your head, AT 1 GPM, is greater than 3.5 feet. Now, that would be an extraordinary feat that probably can only be accomplished with seven miles of tubing."

Only about 950' per 4 loop manifold of 1/2" pex. Loopcad says on the 65 degree day a single zones will have 1.7- 2.2 ft hd / .50 - .84 flow but this brings me back to water temp. I am not sure i understand what loop cad is doing, originally i chose the option of locking delta T which i chose to do at DT10, then at gordys suggestion to lower my flow/hd to within ecm curves, I changed that to DT15 [since it was 5 degree increments, but i could see something in between would have done the job.]

I also locked surface temps at 82 degrees for hardwood, I then noticed loop cad was also giving a water temp. great i thought because what i thought was happening is, it was giving me the water temp and delta t that i was to enforce through controls.

But I later noticed it had the individual return loops dt all over the place some as high as dt 55. I am half understanding it might be adjusting for loop differences on same manifold. {that different rooms/ different loads with an assumed same flow, dt varies but flow meters will compensate????]
I keep saying Im not up to speed if this is normally done but my novice inclination is to enforce dt with the dt pump. yes it may vary a bit within loops and the different manifolds on the zone may differ a bit more but if the average of them all is design dt how bad could it be, and i think flow valves would compensate.

You say since it will not be able in reality to reduce flow because low head? Is this because pump curve and pump has a minimum and we are pushing on a string? asked someone earlier what happens below the pumps curve, does it refuse to run or jump up and start running up at the curve bottom. Soit cant physically pump down below the curve ?

If the head is 3.5 feet or less (AT 1 GPM), the VT2218 can NEVER flow less than 1 GPM and the boiler is, in theory, fine with it.



I would like to see you install the VT2218 on the KHN. I believe it will do well for you.

I would like that too

Talked again with the KHN guy i was told knew more. Regarding the boiler controlling pump without P/S honestly he sounded like he didnt really know or understand what the engineers told him. What he told me was yada yada algorithm, when i tried to press him to say algorythm meaning minimum flow through boiler, he seemed to not think so just algorythm, maybe competing algorithm? but the normal 0-10v of which they are specific pumps dont have rhythm as far as i know.
I simply dont understand why you can control a pump externally w/o p/s but there's a problem controlling it internally id think the opposite was more problematic.and when someone cant explain it i dont think they know either.

he did say though guys are using bumble bees so ecm, and delta t are not the problem.
And you can definitely ramp it so it will fire and stay on lowest mod for time you set.
and he confirmed you can certainly control your pumps externally many ways, bms included.
and i see besides that little ecm board control there are all sorts of 0-10v input/ pwm output interfaces to do exactly this for hvac pumps and fans, cost might be a factor, supply house wilo has dual pump box for 175.

keyote

So guys what if as i said i make the indirect DHW the primary [only]loop, so low load calls are bled off indirect heating with z valves even the tank could have a zone that closes when more Ch is needed, this solves flow and modulation and one pump to rule them all

keyote

You have four zones and they each have a maximum of 2.2 feet at .84 GPM? Yes on the 65 degree design day the lowest head zone is 1.7 hd .77 gpm the highest head zone is 2.2 head .84 gpm and 1.8 hd .5 gpm and 1.9 head and .60 gpm according to loop cad
the 17 degree design days 4 zone total TOTAL head is 8.2 plus boiler and 7.6 gpm

keyote

Just follow speed 1 on the VT2218 curve to see what it does. If the head gets down to 1 foot, the VT is going to deliver 5 GPM. It will run perfectly fine and no it won't "jump up".

In reality, you never get below the speed 1 curve. That is the slowest the VT can run.

so then i suppose i put in a by pass loop so the rest of the water can just go back through the boiler?but put the pump sensors behind the loop? and the boiler is told to make say 110 degree swt that day so just keeps doing that but will it short cycle the burner now or can it sustain that

hot_rod

I thought this 15-42 VS pump was no longer available, but I see Supplyhouse.com still offers it. It should communicate with the Lochinvar 0-10VDS signal, and I think the curves work out, although not sure what you have decided on the required flows?

Having the circ take orders from the boiler control makes most sense, I think.




SH.com does have all the manuals for it on the page.

It's not for the cheap of pocketbook shopper.

keyote

Thank you hot rod I understand now what you meant days ago about the ecm pumps and boilers they need pwm and american boilers us 10-1vdc, at the commercial level there are interfaces that work it out.
Im wanting to use ecm for efficiency, but lochinvar is not liking having boiler control pump without P/S, though they cant explain why besides mumbling algorithm, they do say the bumblebee is working when externally controlled so i dont see why the 2218 wouldnt as well which is better sized for my system.
Hat thinks the fact that the 2218 cant pump any slower than 3 gpm at low head on warm days and single zone calls will guarantee flow. I had another crazy idea of using the indirect to bleed off flow and even BTus on low load calls has that been tried? Instead of giving it priority the usual way make it a zone that opens with the first Ch zone and if need be closes as the load increases. The Ch zones would need a tempering valve of course but now you not only dont need a Primary and secondary but you dont need a separate DHW pump just
One Pump to Rule them All

hot_rod

P/S, hydroseps and buffer tanks pretty much assure that the boiler will receive adequate flow. That makes boiler manufacturers smile! They hate failed product, especially when it is preventable operator error. that is probably why they push everyone to separation of some sort.

It's also hard for the factory guys to get a clear picture of your system and pumping requirements on a short phone call, they get dozens a day, I suspect many callers cannot answer the questions they ask and need to know to give you and exact answer. It is hard for them to judge your experience in a short phone call also, so the safe option is usually promoted, I suspect.

And... they don't know all the ins and outs of every pump or device on the market and how it relates to their control. I think Lochinvar does offer the Grundfos Magna ECM vs for their larger boilers systems, right from the factory as they have tested it extensively and are confident in it's performance.

My son worked for the Lochinvar rep in western Colorado for 4 years, so I got to see some of the newest products and methods that progressive installers are using. A very small portion of our industry hang out here, unfortunately. I visit shops that install 100's of boilers a year and have a lot of hands on experience with the newest technology and methods.

The Rockies in Colorado with it's weather, fuel challenges, long heating season and altitude is a favorite testing ground for the top boiler manufacturers. Prototype product usually spends a few years out there before you see it on the shelves, the reps in that area help oversee and manage that process.

keyote

HAT
8000 btu / DT10 / 496 [100 degree water constant ] =1.6 gpm not bad for a tinkocker huh, thank you,
so youe saying if the pump is forced to maintain delt t 10 while the boiler is giving the flow 8000 btu its going to have to pump 1.6 gpm
UNLESS it cant get rid of the 8000 btu before it gets back and re measures RWT? got it so far.

Yoy say
"If one zone calls and can only deliver 4K, the VT is going to try to slow the flow down to .8 GPM.........which is below the minimum spec for the boiler."

thinking outloud it only dropped 4000 btus [about right according to loopcad]
and now the dt is is about 5?

the ratio of heat output to flow is non linear but increases with flow so the pump speeds up not slows down? to to deliver more heat and decrease DT?

The boiler could not deliver less heat and the RWT is very close to the SWT setpoint so it soon shuts off.

keyote

Hat

Yes i may have to at the least put two manifolds on one zone valve to get to low mod on a spring day at which point its half the house and zoning is meaningless.so

yes the buffer shines
but by definition its a two pump design which we hate right? yeah we hate it less than close tees because at least we can fire the boiler and primary less often but still it wasteful, and i might as well forget the lochvar and make do with the TT110 if im going buffer no?

but at the risk of being ridiculous again and maybe only ignorant Im proposing using the indirects loop as a kind of buffer, but one that doesnt need a second or third pump and which standby energy is utilized.
Im sure it a very tricky calculation that probably only a simulator could figure out how it might operate under all conditions indirect size might need to be changed to make it work, and controls could get a little complicated to make sure DHW recover despit CH demands but i bet it might be able to work

Gordy

In light of your future addition then the 85 would be a better choice. I disagree with hats comments on my post in that the 55 is going to be a bit cheaper. That, and a standard 40 gal gas DJW heater has less input than the 55 on a priority DHW call.mso if you can get by on first draw who cares about recovery.

In reference to how many baths, bars sinks etc. does not matter it's the usage. I use a standard gas fired 40 gal with 2 daughters,and a wife never ran out of hot water. All though I leveraged capacity by higher storage temps. You can do the same with an indirect. Tempering valve is a must.

So yes you can lock out modulation. The boiler will cost more. the fallacy of recovery is only true if you have high gpm shower residents taking 20 minute showers, and large Roman tubs.

My family chooses not to dwell in those realms.

Brewbeer

Why do we hate the two pump design when used with buffer? With low head the pumps can be small or run on low. For example the VT on low is 9 watts. Two running on low would be 18 watts. Running 24/7 for a month they would consume 13 kw, or about $2 worth of electricity at $0.15 / kw.

keyote

I guess my thought was if the indirect zone opens whenever the first CH zone calls [and closses when two ch zones are calling], it makes the demand load bigger, so if the ch call on a spring day only needs 4000 btuhr of the 8000 btuhr the boiler produces on lowest mod, the indirect can soak up the rest, and i was thinking if the minimum flow on the 2218 was more than desired it could soak up that too? The external tank is 8 gallons. but unless theres a way on dhw only calls to tell pump to ignore dt signal and pump full speed you would have a problem to solve probably with a dedicated pump of course it would not be used as much

Brewbeer

Indirects generally are set up priority, you wouldn't be in space heating mode if you are heating DHW.

Brewbeer

Also, the indirect stores water at a temp higher than what the radiant system needs for 90+% of the heating season, so it can't "soak up" excess BTU that the space heat zones don't use, since low space heating demand will occur on milder days when the ODR will have the SWTs dialed back.

Gordy

And yes it is far better to have boiler sizing on the edge than oversized. Any boiler loves mass to run efficiently.

If your heat loss was 52k ,and your inputs conservative you may be as low as 42k in real life at design. That only happens 2% of the season. On the he other hand I have seen design days drop well below recommended deign temps. Heck my design temp is -9. I have lived through -27 multiple times.

To give an idea on an average day my system is in call 3-4 hours of 24. At design 5-51/2. Below design of -27 it's been 8 hours. R values increase slightly as temperatures drop. R values are based on 75* mean temperature. Unless you look at sips then they base r values on 40 degree mean temp.

So,what am I saying.... The most efficient boiler is one that is off. Next comes one that can manage the load precisely. Possibly if a well done design of system, and controls is accomplished with a boiler that fits the heat load perfectly it would never shut off during the heating season, and have low return temps in the high 80's that would guarantee 95% efficiency . Then there is the pig with lip stick that needs mass, to make it run efficiently. This adds extra capital cost to the system, but can still get higher efficiency.

keyote

this didnt post with the description

keyote

I see what youre saying gordy Im going to study my design a bit more and think carefully about where and in what direction it might be off, and how low i might be able to get the load of an addition.
Am i hearing you correctly that its better to have a boiler thats technically below your heat loss calc and let it run a little longer on colder days maybe even 8-12 hours on really really cold but rally rare days?
i have thought i might explore radiant ceilings for the other floors would that impact. my guess is the 55 is the same price or close

keyote

Hat I agree it seems like less risk which is why i was going that way, but i think gordy is saying running it at 10% - 65% is less efficient which is our goal. I need to understand mod cons better

keyote

Brewbeer in a sense youre right and its a challenge thing,on the other hand they would be using twice as much power as they need to if i can solve this,its solvable the boiler makers all have non P/S options but it can raise a few issues to watch for. same with the dedicated buffer while probably better than just circulating water through close tees if it gets used before it cools but again we have a boiler that goes 0-60 in a couple secs why not take advantage. Im putting solar electric and water panels on the roof I would like to be as close to autonomous as possible you never know when zombies will cut your power off
to answr your question about the indirect temp v radiant temp youll see in the drawing i have a mixing valve on the radiant headers, The indirect will be getting a bit of heat whenever only one zone is calling for radiant and the indirect zone will close whenever a second radiant zone calls because i will then easily be within range of boilers lowest modulation and flow requirements and Im guessing the danger will be over heating the indirect this way. so i would say you do this as seldom as needed and if the indirect still needs a bit more then it will put in a priority call. the big question is at what point is the priority call allowed other than recovery and how can you get a DT pump with its sensors on the radiant headers to ignor the sensors and pump full speed for the priority dhw call answer that and we have one ring to rule them all

Gordy

You have to remember building mass will shoulder you through below design conditions. Mostly the coldest part of the day is early am. By then you are transitioning into day light where solar gain takes over to pull you out.

Most bitter cold below design, or design conditions are clear skys,

Gordy

However you start doing setbacks, especially deep ones that all goes out the window.

Brewbeer

keyote said:

to answr your question about the indirect temp v radiant temp youll see in the drawing i have a mixing valve on the radiant headers, The indirect will be getting a bit of heat whenever only one zone is calling for radiant and the indirect zone will close whenever a second radiant zone calls because i will then easily be within range of boilers lowest modulation and flow requirements and Im guessing the danger will be over heating the indirect this way. so i would say you do this as seldom as needed and if the indirect still needs a bit more then it will put in a priority call. the big question is at what point is the priority call allowed other than recovery and how can you get a DT pump with its sensors on the radiant headers to ignor the sensors and pump full speed for the priority dhw call answer that and we have one ring to rule them all

Why run the boiler hot and then mix down for the radiant? You loose efficiency this way. Run the boiler at the temp required by the radiant without mixing. For the priority DHW, just run a separate dedicated pump.

keyote

Gordy your on call numbers are interesting in a situation like mine i wonder how often i will have only one zone calling or how long it would take to meet a call.Yesterday i did look up the days below 40 days below 30 days below 20 interestin i should average 16 design days a year

keyote

brewbeer If you mean you may not be taking full advantage of consing yes thats a possible drawback but id have to know more about all possible conditions to be sure. Bt if you mean because we are running at 140 and mixing down i dont see how you are right. heres why we are simply putting 140 into the indirect that we were going to anyway maybe a bit sooner maybe a bit later and its not a big change because this only happens when a single zone is calling and stops if another zone calls too. But it not only allows us to avoid a Primary and a secondary pump but also a separate indirect pump so one ecm instead of three regular pumps it also kind of eliminates any tought of zone pumps instead of valves. how many pictures of boiler roons have you seen with seven pumps for this system. one on every riser one on the indirect and a primary and a secondary. its like plumbers own taco stock.

But that aside for a minute. This comes about because I had a problem that kept leading to more problems ,even a 10-1 modulation down to 8500hbtuhr which is todays state of the art is more than an entire floor of a 5000 sf house needs on even design day, and on a 65 degree day its more than two floors need so zoning becomes impossible without a buffer.Houses used to leak like seives and if they didnt oil was cheap and windows were sufficient for zoning. I dont think like that no one i know does we all want platinum leads efficiency and to be able to zone the heated towel bar and no matter how ridiculous that may sound to you I promise you they are going to get what they want and soon and money will be made.To me its a game to them its a carbon footprint and status.
So the original problem was eliminating pump using ecms and how to get even a moderately sized zone without too low a flow and too low a load.and the answer i kept getting was add pumps and buffers etc basically you can pick where youre going to waste the energy but youre going to waste it somewhere.
i figure out how to get the ecm to behave differently on priority dhw calls two set of dt sensors one on dhw one on the radiant headers relayed through parallel switches that lock each other out.

keyote

Hat i had thought a simpler way than my crazy invention was simply accept that i would have to gang a couple floors together or maybe just make the entire house a zone
But explain please how i would do what you suggest do i adjust the flow meters to sort of starve the loops so they cant keep meet the dt?
Btw you never said when dt is narowing does the pump speed up to be able to deliver heat faster or slow down to let the boiler get ahead of it

keyote

if the flow meters are dialed in like that will it hold if the boiler raises the swt for outside temperature drop.

Gordy

Pay attention to these charts. The return temps, modulation range that gets the highest efficiency. Your emitter required water temps will dictate supply temps. Your delta will dictate return

The boiler has Dhw priority. It only comes on when the indirect needs replenished. The rest of the time that boiler sends the required water temps out to the emitters dictated by your ODR curve.

Gordy

Pay attention to the temp differential though 20* delta. You start to narrow that efficiency plummets. Widen it, and it climbs.

This where the emitter selection, and design is crucial. Existing your hands are tied. New design opens many doors.

Gordy

One other thing that runs across all sources. The lower end of modulation gives a higher efficiency over a broader return temperature range. As modulation increases that temperature to efficiency range plummets as you approach 130*.

Gordy

Now apply this to a direct pumped boiler that is NOT forced to maintain a delta. As the boiler fires on a call from cold start the initial efficiency will be higher because the rwt will initially be lower. The delta wider. As the boiler approaches set point the rwt climbs in unison with the swt. Until swt hits the ODR curve setting for the conditions. If the zone is still not satisfied then the supply return temps stabilize at a given delta until the zone is satisfied. This all pivots on mass the more mass the longer it takes to pull the emitter up to its operating range.

You start to force a delta right out of the gate you lose that initial approach of low return temps where the boiler will see a wider delta for a bit.

With the panel configuration keyote has the btus will not jump off the train as easily. They will get sent back to the boiler for another lap.

Now that is one way to look at it.


I have always viewed the delta hitting its design approaching the end of a call. Not the full time of the call.

IF the emitter, the flow rate, and boiler output are in perfect unison the delta can be darn near the same from start to finish. That takes proper design.

I think the best option is the VS circulator controlled by the boilers logic.

The vitodens 200 has been controlled in that manner for years. To us it was mysterious for a long time. I still remember miketswampeast euro cave thread from many moons ago. A vitodens 200 direct piped to a gravity system with standing iron, and trvs.

That in itself just shows how long it's taken the North American market to try, and catch up, and there is still the disconnect of vs circ, and boiler logic.

Brewbeer

keyote said:

brewbeer If you mean you may not be taking full advantage of consing yes thats a possible drawback but id have to know more about all possible conditions to be sure.

It seems like you are trying to maximize your system efficiency, that's why I asked about the mixing down for the radiant. System efficiency gains from condensing aren't an all-or-nothing proposition. The lower temp you can run the boiler, the greater the boiler efficiency. It's odd you would mix down the radiant, since you are trying hard to avoid using primary/secondary, (which when not balanced is in effect mixing which is reducing boiler efficiency).

Aren't the controllable 0-10v ECM circulators basically the same cost as 3 more traditional circulators? There doesn't seem to be a compelling reason to not use a dedicated pump for the priority indirect.

Gordy

In the drawing there is no need for a mixing valve. On a priority domestic call the zone valves for CH would be closed until domestic call ended. Then the CH demand would be satisfied at the ODR curve. So no need for a mixing valve for radiant emitters.

The boiler will always suffer an efficiency hit on a domestic call. However making Dhw with an efficiency of 82% verses 50 or 60 is far better.

SWEI

Brewbeer said:

Aren't the controllable 0-10v ECM circulators basically the same cost as 3 more traditional circulators?

The smallest 0-10V controllable ECM circulators I have seen to date are the MAGNA3 32-60 (currently out for a redesign) and the Stratos 1.5x3-20. Way too much for anything smaller than a 399k -- and even that is working the bottom of its curve when paired with a FT boiler.

keyote

Gordy wow thank so you very very much that's just the info i needed to think about, I had a general idea but was feeling guilty for not refreshing myself on why i choose to go modcon years ago.my lazy thought was with a radiant system I shouldn't have to worry too much because by definition my RWT is going to be low. Loopcad was telling me 127 degrees SWT on design day and 91 degrees on 65 degree day giving me RWT at say delta 13 of 114 and 77.
But "low return temp is a relative term and i had no idea what temps they meant exactly, and had a vague awareness it was dynamic with other factors which I really needed to look into.So thank you for putting this in my hands.

If i am understanding you and the charts correctly one other factor is where in the modulation band you are while the RW is coming in, Meaning Hat is correct, oversizing in my situation is going to force it to run more efficiently.
Using the headline BTU with the KHN 85 vs the KHN 55 on design day of 52 KBTUHR I would be running at 60% modulation instead of 100% and on 65 degree day I would be running at 20% modulation [less if all zones dont call at once] instead of 33%.

The other factor is Delta T shown on the vitodens chart it shows two things one is that narrower dt is always more efficient but less so as you move down the modulation band the curve flattens. Its cut off too soon and doesnt go up to delta 10-15 but one can imagine an almost flat line above the three other lines. That implies maybe with low radiant dts modulation point is not as important, but it doesn't actually specify if or how this changes with with RWT which the other charts imply is going to matter significantly.
Granted in my situations the difference between the KHN 85 v 55 is only going to be 3-5% its good to know that the margin of error wouldnt cost in efficiency. It should be a rule of thumb then to size boilers to the higher indirect load.
That said it makes me nervous I dont understand why loop cad had individual loop RWT all over the place when i though DT was locked Im hoping its their way of saying you have some balancing work to do with flow meters. It turns out although i can no longer export files or even save changes any more i can still make changes and see the interactions until i close it then it reverts to my design on the day last trial day.

Gordy

The grundfos VS family hot rod posted is the ticket. Actually the KHN specs it in the manual for VS pumping. The 26-96 actually.

All though not an ecm variety the gain in coupling pump speed to boiler modulation may wash what lower ecm wattages gain.

Become intiment with the KHN manual. Page 39,56 covers options on how VS can be used with the smart system. Note one option requires p/s piping.

keyote

Gordy
"Now apply this to a direct pumped boiler that is NOT forced to maintain a delta. As the boiler fires on a call from cold start the initial efficiency will be higher because the rwt will initially be lower. ".....
Im trying to understand this, Its important to me because im leaning to this VT2218 DT pump partly because its an ecm whose is curve is wide enough for me on the low and high sides, admittedly it also appeals seems because it helps my amatuer mind with thinking about control because it partitions aspects that otherwise interact and get my head spinning-Or so I think
.
Considering your comment is hard because I dont have experience thinking about the time scale for various systems which i think is the crux, but I may be clueless, Im imagining some huge old atmospheric systems pumping large amounts of water needing to be heated much hotter and this all takes some time to ramp up but the ramp up does a fair amount of partial load meeting, and in this system if it were on a modcom which i dont think it would ideally be then a significant portion of fire time would be essentially warm up.
But [and i could be wrong] in a system like radiant or a small baseboard the water can make a full circuit in seconds and would be better off being at the right temp asap, its warm up is too low temp, and happens to quick to make any meaningful contribution to load.This worry about high limiting on start up I have and Hat experienced is possibly helped by micro version of this but i think thats more a matter of syncing than efficiency, But i may be not getting your point.

Gordy

Your getting some of it. As a general rule you can not apply oversizing to all mod/cons. Only the 10:1 with the ability to lock out upper modulation steps. You still have to pay close attention to the low end modulation on the 5:1 mod/cons.

The only time sizing to domestic loads becomes the lead is when ch loads are in the weeds.

Not s