Buffer, boiler, loads interface via Caleffi (hr)

Paul Rohrs

How about this buffer tank in series with the Caleffi? Easy to pipe an indirect off of this. The Hydrolink is a product whose time has come.

PR

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hr

Lots of interest in buffer

set ups these days. I've been noodling way to make the piping and layout quick, correct and compact.

I think the Caleffi HydroLink could be the missing piece!

Here is a drawing and a pic of one I working on in the shop.

The HydroLink gives you a good solid platform to build from, keeps all the hydraulics in harmony. It also gives you an excellent air purger and rock solid expansion tank mount.

Any thoughts?

hot rod

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Cosmo_3

I love'em

It is a shame that more manufacturers aren't making these. Caleffi is a great company that makes products that just "make sense"

I have used the Hydrolink more than a few times, and it is awesome!

Well that's all I have to say about that.....

Great job Hot Rod!!!


Cosmo Valavanis

Dependable P.H.C. Inc.

Ron Schroeder_4

Hi Paul,

That piping doesn't allow heat to be pulled from the buffer without it having to go thru the boiler too. Especially for micro loads it is best to seperate the boiler from the buffer.

Ron

Paul Rohrs

Ron,

I think this piping ESPECIALLY allows heat to be drawn from the buffer tank when the boiler isn't running. The boiler is separated by closely spaced tees. Boiler circ purges after the boiler shuts down and primary loop circ in series with the buffer distributes heat to the caleffi. The Hydrolink enjoys the mass of the buffer and the hydraulic separation of zones.

PR

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Alex Giacomuzzi

I Like the Buffer Concept...... PLEASE FORGIVE ME!!!!

I like what I am seeing on paper...
Paul you are correct.... The flow does not have to go thru the boiler. You mentioned series.... that may have triggered the comment from Ron. You have an interesting design concept..

Here is what I see from this piping schematic... and I would like to add one more item to what you have shown. Can we add one flo check valve between the 2 closely spaced T's from the boiler with the flo check pointed toward the buffer..

With that piece in place........ we can run only one pump --- the boiler pump and charge the buffer. If there is an extended run, the boiler pump and the buffer circulator pump can both run supplying heat to the loops. The boiler could be running anywhere from full on to some degreee of modulation..

Now if only the loops are calling and the buffer is satisfied ---- the flow would only come from the buffer.
The buffer could enjoy outdoor reset and the boiler could just be modulating. There can be times when large zone loads call where the modulating boiler might run in parallel with the buffer circ and the respective zone circ's .. For those micro loads which are very intermittent and possibly much to small for the boiler to run ---- only the buffer circulator need run and the micro circulator would be running also.

Lets assume all loads are satisfied........ the disconnect capability of the Caleffi can if you choose to run any or all zone circs. in a constant mode if you choose to. Since we are normally loosing some degree of heat from the zones normally continuously, if the buffer circ were variable speed, it could inject an appropriate amount of heat into the Caleffi to be distributed into the zones in a minimalist manner...

That is just a little bit of energy constantly going into all or most of the heating elements.......


There you go....... more than you maybe asked for..
Pardon me for being a bit wordy.... I get that way later in the evening... What do you think??..

Regards Alex

gasfolk

Questions...

This looks nice and simple.

1) Does this piping scheme addresses concerns for prolonged condensing temps with CI boilers?

2) If all loads are low temp (less than 125F max supply, is there an approach using fewer pumps?

Thanks,

gf

Paul Rohrs_4

info

Gasfolk,

I have only been using condensing boilers so this would NOT address sustained flue gas condensation. As to circulators, I would need more information about zoning ie-high temp, low temp, etc.



Hotrod,

I really like your set up. It seems I am continually fighting for space in the mechanical room. I am noticing that you look for maximum performance with little room.

Question: In you current setup, the zone circulators can have a reset temp to it, until the DHW zone calls and takes priority (?) Then the space heating zone circulators are suspended until DHW is satisfied ? So the Hydrolink will have reset temp until the DHW calls, then the H-link gets 180°F + water temps. I like it, I like it a lot! Clever.

Regards,

PR

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gasfolk

Question, part 2

1) We eventually will get a mo-co boiler, but for now, is there a simple way to use this setup with CI?

2) Would you get colder return temps to the boiler if the returns didn't pass through the Caleffi, and if so, do you expect much change in efficiency.

3) We circulate the same supply temp to all zones: Two small RFH (master bath and kitchen, on the same pump and Tekmar control with sensors in the MBath floor), and one whole house gravity conversion (paired NE and SW supplies and returns--could be two zones, but on one pump controlled by one thermostat).

Ron Schroeder_4

Hi Paul,

I was really refering to the first picture, not your second one. Your picture for some reason didn't come up on my computer.

I agree with you on your picture.

What would make it even better would be to pipe the boiler into another set of ports on the buffer (if it had them) with the boiler supply going into the top of the buffer and the boiler return connected to the bottom of the buffer. Then you could take advantage of stratification in the tank for even lower boiler return temperatures for more condensing.

Ron

Ron Schroeder_4

Hi gf,

I think I would address the low return water temperature to a CI boiler with a Danfoss/ESBE thermostatic bypass valve.

Ron

Ron Schroeder_4

(quote)Here is what I see from this piping schematic... and I would like to add one more item to what you have shown. Can we add one flo check valve between the 2 closely spaced T's from the boiler with the flo check pointed toward the buffer..

With that piece in place........ we can run only one pump --- the boiler pump and charge the buffer. If there is an extended run, the boiler pump and the buffer circulator pump can both run supplying heat to the loops. The boiler could be running anywhere from full on to some degreee of modulation.(quote)

Hi Alex,

Interesting thought but the flo-check would upset the low pressure drop needed for the closely spaced "T"s to work. A low loss swing check between the "T"s and a flo check to the boiler might allow your concept to work.

Ron

Mike T., Swampeast MO

Dumb question about your drawing Paul:

How does the buffer charge when zones aren't calling? Does the manifold have some sort of device that links supply with return when no zone circulator is running?

As is it looks to me like the buffer can only charge when the boiler circulator, buffer circulator and one or more zones circulators are running.

Paul Rohrs_4

I like Hotrods drawing

and my drawing was variation of that.

My thought was that on a call for heat, the boiler will supply the primary loop and "charge" the buffer tank. When tank is satisfied, boiler purges, but the buffer tank in the primary loop circ continues to supply available reset temp H2O to the Hydrolink. Buffer tank will only charge when zone heat calls.

My preferred method is still this way.

Regards,

PR

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hr

Inside the Caleffi and cast boiler idea

There is a bit of mixing going on inside the HydroLink. I've tried to pick the engineer that designed it brain as to how they calculated that port size. Maybe I need a trip to Italy to consult face to face

What's that you say the Milan heating show is the end on next month Hmmmm, I wonder...

An option for a convential non condensing boiler would be a VS delta t pump. Sensor on the return to vary the speed, since cast boilers are not real flow sensitive. May as well use the circ for double duty as opposed to a thermostatic mixer.

hot rod

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Unknown

this might be a dumb question, but what is the point of a buffer tank with a modulating boiler?

for very small loads?

Alex Giacomuzzi

Lets Go.......

HR ---- you need someone to carry your bags...? Italy sounds great. In fact --- my wife and I were just chatting about going last night...

If I understand the Hydrolink ---- it allows hydraulic uncoupling or independence I believe of both the primary and the secondary loops. Now there may be some restrictions on how much you can flow and still get that separation, but if you are below their specs.... there should be uncoupling available..

Having said that.... a secondary pump to the zones should not be required to run to charge the buffer --- again if I am viewing this correctly.

In some ways ---- this is a very compact header system comprised of inlet and outlet T's for the supply and for the return headers with a close coupled fixed circuit setter ( which allows blending in either direction) piped between them at their inlet.. Compact and functional for flow separation (or interference). Nice and interesting piece of hardware

Ron ---- You are correct regarding the added resistance of a flo check, but with many of the mod conds that might be negligible ---- If it was a concern ---- a swing would certainly be much less resistive.

Paul... Why would you pipe the DHW off the primary loop and not directly off the boiler (secondary) loop? It seems --- when it is in the primary loop you need to elevate the buffer temp also to heat your DHW. Where as if it were piped directly off the boiler loop --- it could go to high fire for DHW and then return to modulation temps for the buffer.. Or did I miss something here??
I am always interested in learning a new way.

I do not own a mod cond boiler, but I do have a buffer tank with a CI boiler. After reading several of Mike T's graphs on this web site (which I enjoy and learn from) and understanding that he basically has his whole house as 1 zone in a relatively high mass (standing iron) system ---- and he gets burps of heating. This is on a Vitodens. I understand he is running a bit cool this season....
If one were to design a low mass multi zones or worse yet low mass mini zones that call independently, or where each zone has its own zone valve ----- even though the system is on a modulating boiler ---- you are going to have (possibly) more cycling that you would desire. Therefore a case for a buffer.

Now some designs such as existing gravity system have much of that already built in. It is not a one choice fits all senario, it really is an application related question for the specific system design.

Regards Alex

hr

I did pipe one indirect

off a HydroLink. Not sure what I was thinking

One problem was the wiring. The ultra has DHW priority. However it shuts down the boiler pump when it fires the indirect tank. I had to do some fooling to have both the boiler pump and the DHW pump run together. And to make sure none of the zone circs could call, other wise they would send that 190 to my under floor ThinFins. Ouch! Took a few more relays then should be needed, to make all that happen

And it sort of, kind of has the boiler pump and indirect pump in series, depending on how that blending chamber works in the HydroLink.

That 230K Ultra connected to a 92 gallon Viessmann tank is the mother of all DHW production units, as a result of all that Tom Foolery.

hot rod

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hr

Rob

it's because us hydronic-aholics can't leave well enough alone. We are driven by the challange that it can be tweaked and improved upon.

Just the nature of the beast, I suppose.

hot rod

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Paul Rohrs

It just looked

like hotrods last drawing had 3 circ based heat zones off of the Caleffi and one zone feeding a DHW/buffer. I thought maybe he was heating DHW off of the secondary piping of the Hydrolink. (Pic posted at 7:16)

Hotrod,

I can pipe DHW off of the boiler loop, I just like the added buffer of the primary loop and using flow-checks and isolating for DHW on priority. I picked it up from of a tekmar drawing. Tekmar 265 and 263 with DHW (mode 2) piped as parallel primary, dhw post purging and bringing the loop temp down before resuming space heating.

I have piped a few Munchkins with Vision 1 as prescribed right off of the boiler loop. I

Regards,

PR

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Paul Rohrs

10-step program

is awaiting me somewhere. Scott Milne too I believe.

The reverse indirects really make me wonder about the usable gpm available. I just have not seen one, for me it's kind of like the "Bigfoot of Hydronics" seen pictures, heard rumors, but don't think I want to try to hunt one down until more numbers hit.

Regards,

PR

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Unknown

Fair enough am I right to assume that the buffer tank only really helps when you are under minimum modulation?

I could see it with a more conventional boiler though to even out firing times. perhaps?

am I on the right track?

Paul Rohrs_4

Rob

Yes, even the Lochinvar Knight 80,000 BTU low fires at 16,000 btu's. If I have one small radiant zone calling at 5,000 btu's...short cycle city. Buffer tank just adds mass to the loop to extract heat from. Longer on times, longer off times.

Regards,

PR

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Mike T., Swampeast MO

Thanks for the pic of the inside Hot Rod! Now I see how the buffer charges!!

As drawn it looks as though return temp is intentionally raised. Doesn't this make it less than idea for condensing applications where you want the return as low as possible?

ALH_4

?

I see a buffer tank on a modulating boiler as unnecesseary in most situations, particularly where TRV's are used. At low fire, even modulating condensing boilers are too large under certain circumstances, however they are still only 20%-25% of what the boiler output would be if using a conventional boiler. There are times when the heat load could be less than 5 btu/sf, but is there not enough water volume in the system to prevent severe short cycling under these low-boiler-output conditions? I am beginning to see constant circulation with proportional flow as almost a requirement when using modulating condensing boilers. Also the buffer tank keeps the boiler from seeing the coldest return temps.

Please correct me if I am wrong in these observations.

-Andrew

Unknown

I think I'm with you andrew.. even if you lose a little efficiency at those low loads.. how long is it going to be to pay back the buffer tank, given that the volume of heat you're using during those periods is so low anyway?

to take an extreme example, if you save 10% efficiency on a 1000 BTU/hr load, then it will take you almost 1,000 hours of operation to save a therm of gas. right?

Mike T., Swampeast MO

"...particularly where TRV's are used...is there not enough water volume in the system to prevent severe short cycling under these low-boiler-output conditions..."

I have exactly such a system. TRVs, condensing/modulating boiler (Vitodens) and high system volume (gravity conversion with standing iron). By results of HVAC-Calc boiler is actually a touch undersized.

Under low load conditions I can only describe the boiler operation as "pulsing". VERY short, highly regular firings at [I believe] full output. Viessmann tells me this is normal--when I think, it makes sense to give heat in small batches to such a system when load is really low.

This operation mode occurs in my area quite frequently--especially when I'm saving loads of gas by keeping the place cool.

You don't have to take my word for this. Search for posts (especially last year) titled "Vitodens Operation". You'll find .pdf graphs of operation with comments.

Like you though, I don't know if there would be much benefit from buffering in this case. The boiler operates with amazing efficiency in this mode and in the case of the Vitodens, I've been assurred that this type of operation is not harmful in any way. (Such may not be the case with other condensing/modulating boilers as most used here in the U.S. don't have a control system that assumes TRVs for "normal" operation.)

But surely such must increase wear on ignition components...so it might be nice to do something. With just the single built-in pump driving the system, I have no idea how a buffer could be included. Am VERY open to ideas in this regard--just remember that I won't change the "direct drive" nature of the system and Viessmann system architecture is very closed...

Instead of a buffer however, I'd like to incorporate solar. If my numbers are right and I've correctly interpreted insolation data from the hand-dandy nearby agricultural weather reporting station, I can stop the vast majority of the "pulsing" using only a very small storage tank and "dumping" any excess to the DHW. $$ and collector location are my big problems, but I did get the first part of the system--a big (120 gal) Viessmann indirect.

Paul Rohrs

Yes to all

In my market; new construction, low-temp radiant floor heat,multiple zones, mod-con boilers, buffer tanks make sense.

Your points are accurate and well taken.

Regards,

PR
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Unknown

Now, that's a little confusing. Why would the vitodens pulse at full output instead of its minimum output? Are you sure of that?

You know a lot more about it than I, so I'm not trying to say you're wrong, that just seems odd to me. I thought one of the big benefits of modulation is that it modulates down,and even when it's oversized it's running like a much smaller boiler than a conventional unit of the same max output? That is, when it's below minimum modulation it's running like a 16-25k burner instead of its full output?

This is a very interesting thread guys, keep it up!

Mike T., Swampeast MO

The pulses are short--very short--just a very few seconds. Hard to clock such short events at the meter but they really seem to be at or nearly at full output.

From the program sequence in the Vitodens start-up/service instructions, there is a few second period between flame recognition and "heating mode or modulation range".

What [seems] to happen is that if the boiler detects some amount of temp rise within this short period, that the cycle stops before it begins to modulate.

If the cycle continues I hear an immediate and drastic ramping down of the blower. Every time that I've clocked the meter, the input is at minimum (maximum modulation). [This provided of course that no boiler or TRV setting changes have been made.]

Unless the outside temp is dropping very rapidly, this is the beginning of what I call a "burst". These usually last 1-2 hours. With the burner at minimum for the entire period, the supply temperature begins a fairly slow rise and continues to some threshhold level above the computed target temperature. Then the boiler shuts down. Depending on the load, "pulses" resume for some period of time before another "burst".

If, during a "burst", the target temp cannot be maintained at minimum output the modulation level increases--then and only then do I see what I call "true" modulation with graphs virtually at "flat line".

Again, these are my observations and measurements on this system. Systems without TRVs will certainly behave differently. Also, the high water volume might affect operation in some way. Almost no info from Viessmann on the nature of their modulation scheme so I have to resort to direct observation of temperatures, consumption, sounds, etc.

Unknown

interesting. You're doing good stuff there Mike, thanks for the info!

Mike T., Swampeast MO

Any idea how I could add some sort of buffer? The old stand-alone water heater (90 gal) could serve as the tank. I can deal with an added circulator for the buffer component, but refuse to change the emitter loop away from anything but direct, variable speed drive via the internal circulator.

hr

In your case, Mike

isn't the high mass, relativly high volume emitters you have just like a buffer tank?

Hook a small volume mod con boiler to a multi zoned, low volume system like baseboard or small radiant and the need or want for a buffer will become obvious.

Like any other question in hydronic land, run some numbers. Plot your system on the Buffer Tank module to see what cycling the various loads will do to you boiler.

Then it becomes a question of how much cycling are you, and your boiler comfortable with To me, less is better, I like a minimun of 10 min. boiler on.

I wish my boiler never cycled modulate from my smallest zone to my largest.

One nice thing about most of the mod cons is they will data log that burner cycling. With a years worth of data you can determine if the actual cycles are comfortable for you.

Here is my 80K Knight with a 13K load with and without buffer. I go from a 1.3 minute on, 5.7 off to a 13 minute on 56 off with a 50 gallon buffer.

Live with a system under both conditions to see the diffefence.

hot rod

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Mike T., Swampeast MO

isn't the high mass, relativly high volume emitters you have just like a buffer tank

Only when load is greater than half of the minimum modulation.