Primary/secondary via hydraulic separation with Buffer tank


  #41  
Old 03-22-09, 11:43 AM
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You would 'strap' the T T connection on the boiler then, and let it 'free run' I presume.

Rather than change out the a'stat on the boiler, since most are 15* or less fixed diff, might make sense to install an a'stat on the buffer tank and wire that to the T T terminals.

Problem I see with this approach is that you've essentially created a 'warm start' boiler. It's going to maintain the temp in the buffer tank regardless of demand... unless you've got something else in mind to pass the demand on to the boiler?
 
  #42  
Old 03-22-09, 12:45 PM
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I agree running off the buffer well might improve things.

During periods of light load, it will sit and wait. Hours if necessary.

During higher loads, it'll do what all boilers do. Cycle. But the cycles should be long.
 
  #43  
Old 03-22-09, 01:03 PM
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Maybe next season, I'll try the boiler sensor in the buffer well just for giggles.
 
  #44  
Old 03-23-09, 06:03 AM
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Okay, so is the buffer essentially a BTU battery and the boiler just a battery charger? If so, why even bother with an ODR controller for the buffer tank and boiler? The buffer tank works best with a wide set differential.

The heating distribution itself is what really needs the ODR so why not get something like an iSeries mixing valve from Taco? You can even do different ones for different temperature curve requirements. These controls are far simpler to set up and operate.

It seems simpler to me... and the buffer could also provide DHW within its set range (with a mixing valve and anti-scald controls of course).
 
  #45  
Old 03-23-09, 12:00 PM
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Battery and battery charger. Good analogy. I was kind of writing the above for Joe (still thinking) and Johndl (already has a 361).

Just priced the iSeries valves. Each valve is about as much as a decent ODR control.... "To go all-in-one, or not to go all-in-one. That is the question."
 
  #46  
Old 03-23-09, 03:48 PM
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Okay, so is the buffer essentially a BTU battery and the boiler just a battery charger? If so, why even bother with an ODR controller for the buffer tank and boiler? The buffer tank works best with a wide set differential.
I guess one reason could be to minimize 'standby' losses... the hotter the water in the tank, the more 'leakage current' out of the batteries when the system is not calling for heat.

Cooler water in the buffer tank during shoulder seasons is also going to make it easier for the ODR on the space heating side to do a reasonable 'mix'... i.e. you are running a VS pump, and the system is calling for 80* water to the space heating... you've got 180* water in the tank... the VS pump will have to run very slowly... or perhaps pulse... in order to achieve the target temp. If the buffer is only at say 140*, the VS pump will be operating at a more 'controlable' speed.

I KNOW this is way overkill... but, if you were running the 361, AND a 260, with a conventional boiler, you could put the 361 boiler sensor on the RETURN, set for appropriate (10% or 30%) boiler enable... the 260 sensor on the boiler SUPPLY with appropriate settings to prevent condensation (i.e. PARTIAL BOILER RESET). The 361 would do FULL SYSTEM RESET... yes, it's a lot of hardware, but it would be a very efficient setup...
 
  #47  
Old 03-23-09, 08:58 PM
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Troop - But it really shouldn't be a very leaky battery and all the more reason for it to serve DHW functions as well. My buffer (de/re-commissioned 46 gallon water heater) runs at system temps (110 - 120) on average through the winter and I have no qualms about it leaking. Skin temp stays around 75. It doesn't sit directly on the concrete floor. I was gonna do an extra wrap on it, but it was fine. They insulate fridges well enough and they have to open and close all the time and store crap in the door. A buffer tank should be way easier to insulate.

If the whole idea of the battery concept is to extend intervals between firing times and prolong burns, the ODR on the boiler itself will just help keep the battery from getting topped up in the milder seasons.


Xiph, I think a 3way iSeries is around $220. Not bad for a motorized mixing valve and ODR controller. One little pump on the other side of it for heat distribution and you're set. Seems easier and simpler than injection. Second temp required? No problem... add a second iSeries - then one doesn't interfere with the other and they each get a curve. The buffer won't care which it has to serve, it only stocks the BTU warehouse. When the BTUs are gone it'll call the boiler again.

There is no WWSD this way but if the buffer is a reverse indirect (I hope they don't crud up like tankless coils) or something similar to serve DHW needs it won't be needed.

I know where Joe is looking to go and where John has successfully gone but I can't help but think the 361 is the wrong tool for the job when it comes to charging buffers.

K.I.S.S.
 
  #48  
Old 03-24-09, 04:55 AM
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I froogled and got a few vendors in the 320-400 each range depending on size and ports. the 3-way 3/4" was ~350.

So two iSeries are roughly a decent ODR control and two zone valves.

I understand about the charging, and whether the 361 is the best tool for the job. Based on n=1 installs that I know of, though, it does appear to do a good job. Troop is also correct about wanting to have the buffer target a temp that is a balance between injection speed, heating load, runtime, etc.

My reservation about the iSeries is the specific piping required, and going for an all-in-one unit like this. It's not easily undone, and you have x times the number of zones ODR controls. Good in some ways, maybe not so good in others.
 
  #49  
Old 03-24-09, 02:25 PM
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Yes rechecked with supplier, $320 with controller 220 without.

I think the plumbing is a plus. You can have as many zones as you want off of one and if you need to do a separate temp, that is when you could get another as it will need its own reset curve. No injection pump needed. Heck, with panels and TRVs you could probably just use a simple mixing valve and a set output temp that you maybe change in the shoulder and severe seasons.

With the buffer serving also as the DHW you are down to two pumps. One for the boiler that does the buffer/DHW and one for the heating.

Seems well suited to an oil-fired boiler or even something simple on the modcon side like a Vito 100, albeit you would use lower temps and maybe a weekly 140 runup to kill the DHW critters if the tank holds any DHW in it..
 
  #50  
Old 03-25-09, 09:13 PM
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This is the BEST stuff!

You guys are something! This thread is the best .
There will be more use of buffer tanks in future. This is a resource.

Have not digested it all.
Who, can you pencil a sketch of your idea of the buffer with an iSeries valve.
Is the piping so different.?

Probably you all have considered this: The main goal here is to run the boiler longer [and probably therefore hotter. It's not a mod/con]. Its cycles now are short and inefficient.
At the same time, hotter will give the benefit of safe return temperature, but hotter will make for shorter runs when radiators satisfy earlier. So reset is needed, not so much for itself but to make the buffer work. But reset will also help the house somewhat..
The house is comfortable. I am happy I replaced buried-in-wall 1940 fin tube with 3-tube thin tube radiators. Cute little buggers about 2' by 2' by 4". They don't make heat surges. They fit the load. Reset with more continuous flow will smooth out dips I feel at sunset and onset of change in temps. We keep it at 67* but reach for the ubiquitous Minnesota lap blankets at times.

In view of the thought that this buffer could be too hot for smooth reset, what do you think then of this sequence for piping : boiler, mix loop, buffer tank ,system. That is, mix loop before buffer. So only boiler is not reset.??
Or, if buffer is allowed to run hot, just lower the 175* high limit on the boiler. so its not so hot.

Got dusted with snow today, and some ice. Just to keep us humble.
joe
 
  #51  
Old 03-26-09, 05:59 AM
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I'm not sure that this would need boiler protection - I don't think it would (but that's where it would go), but I would leave the pump on the return.

I would pipe the expansion tanks off of the buffer/indirect and then both pumps are effectively pumping away from the buffer tank. Put a good auto air vent on the buffer.

I would put in a microbubbler like a Spirovent on the heating side between the iSeries and the CH pump since much of that water would merely recirculate instead of coming back to the tank. It would probably be fine without it but they look sharp!

The iSeries related piping is in the yellow encircled area.
 
  #52  
Old 03-29-09, 12:04 AM
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Thank you

Thank you Who, Trooper, Xiphias, et al.
It's a kick to see your interaction. Great pencil sketch,Who.

Herself has got me occupied with reading up on South Africa for a trip in a few weeks. Our mostly Irish eldest daughter has found a 5th generation German/ South African lad to marry. Nice guy. Gotta be there. The heating , if any, will not be as intriguing as that in Iceland where we laid over once: Civic central hydronics heated at main plant by volcanic thermal steam. But they lack elephants.

These buffer tanks, in Series, are neither fish nor fowl.
Their temp varies unpredictably ? with the supply in and the draw out of the moment?
That's where the wide- differential aquastat in-the-buffer-well comes into play? To fire the tank up when at low temp. But not up too high. And it should be controlled so the boiler does not fire till the buffer has discharged its heat down to its lower limit?
Have not seen much discussion given here to John Siegenthaler's seeming preference for buffers as a secondary loop. Probably not needed here, as I have no competing loads to heat. It might offer control possibilities.
Wish us luck. joe
 
  #53  
Old 03-29-09, 04:59 AM
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Siggy?

This one shows in series:
September 2007: Rediscovering Hydraulic Separation - Cover Story - PM Engineer

I've seen the pumped buffer article, too. Can't find the link. Would also work, but more complicated. And his article on system simplification (Feb 2008) is well-taken:

Column - Plumbing and Mechanical
 
  #54  
Old 03-29-09, 11:43 PM
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Simple is good.

Simple IS good. And it is good to repeat that. Thanks.

I can point to for Sig. using a buffer on a secondary loop in his book Modern Hydronic Heating which our library happens to have. See Figure 14-39 and 14-40 at pp. 523-524; And in his article Preventing Short Cycling, Nov. 2007 in PM magazine in his The Glitch and the Fix column.
 
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Old 03-29-09, 11:50 PM
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  #56  
Old 03-30-09, 09:24 AM
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I have never found anything simple about that. Yes, the first diagram was a bad install, but I never found his solution to be very simple. There is yet another circ just for the buffer tank alone and then how exactly does that buffer's circ get controlled?
 
  #57  
Old 03-30-09, 04:17 PM
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Oh yeah, that one. Pumped buffer. Not simple. I agree with Who.
 
  #58  
Old 04-01-09, 09:10 PM
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Another

Xiphias, speaking of those other ideas. An amiable guy sent me"Cures for Short Cycling" from one of John Sig's seminars in Las Vegas in Oct., 2003 that had some of these P/S solutions.

I believe one of these is presaged in his PM Mag article of June 2002, "A Signature System". This one is sort of good reading in that it presents a version of the idea we have talked of, of the boiler serving only to heat the buffer tank as directed by a setpoint hi/lo control. Then the system feeds off the buffer on a call for heat.
In his diagram the buffer itself is right in, is part of, the primary loop. [ it happens to be a reverse indirect there].
The boiler is secondary on one side.
The system is secondary on the other.
The control is told but not wholely clear to me. But, hey, what is.
 
  #59  
Old 04-01-09, 09:42 PM
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Column - Plumbing and Mechanical

Pretty complex though...
 
  #60  
Old 04-02-09, 01:26 PM
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Agreed

Agreed. Reduced to its simplest for a mere five zone-valve system with buffer tank, it still requires 4 circulators.

How did you copy and paste that? Routinely? Maybe my problem was trying to just c&p the diagram alone.
 
  #61  
Old 04-02-09, 02:34 PM
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I just pasted the link... I don't do fancy.

Yup... 4 circs when 2 are needed. One between the boiler and the buffer/indirect and the other supplying the heat.

If I get the chance to have another hydronic system, I'm going to go for a very simple layout where the boiler runs to the buffer and the buffer supplies heat and hot water. A big plus to doing it like that if that the buffer becomes the BTU warehouse. It can get BTUs from a boiler or from solar depending on the temps.

The water heater functionality may need to get split into warm and hot tanks but that's for thinking about then.
 
  #62  
Old 10-21-09, 12:09 AM
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Tekmar 356 rather than 361 for buffer set up here?

It is Fall and we have had brief snow. Boiler time!
I could use a quick answer. If indoor feedback is not really needed, can a Tekmar 356 do the job of the
tekmar 361 as we have talked about here, namely to get ODR solely on buffer tank [with PS injection pumping] to work with the buffer tank to mitigate short cycles on oversized boiler ?
I ask this because a Weil-Mclain control that seems a lot like the 356 is available cheap. With four zones and T-stats here and there we get responsive localized adjustment so indoor sensor is not needed..
joe
 
 

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