Unusual multiple boiler piping?

ScottSecor

We have been installing commercial hot water systems for many years. Learned how to pipe primary secondary from Dan and a few boiler manufacturers in the early 1990's. Never saw one piped in this method.

Please see the drawing and share your comments. The drawing is conceptual only and by no means to scale or complete. Note these are not "twin tees" on the header that each boiler connects to, in fact they are equally spaced 6" x 3" welded steel tees (3" on bull), eight in total. I had to insert twin tees for the program to accept my odd piping arrangement

mattmia2

So there are 2 pipes magically connected to the bull of the tee in parallel? There is some detail missing here.

It would work of you constructed 2 concentric pipes or a pipe with a partition to to connect into the tee.

Mad Dog_2

Odd, but it was working for years like this, Scott?  Mad Dog 🐕 

hot_rod

So the load is within the primary loop?
This is not unlike some of the early Gil Carlson designs.
Assuming the boilers connect via close spaced tees?

EBEBRATT-Ed

I have seen this but on chillers. Each boiler/chiller gets a different return water temp if all are operating. I think @DanHolohan describes this somewhere but can't remember where. Maybe it is in "primary secondary piping made easy"

Not good for the usual heating cooling system but have seen similar piping on process loads

Mad Dog_2

My first questions remains:  was this working at one time, how long, how well?  Unorthodox designs challenge logic sometimes, but if you study it long enough, you see the designer/installer knew his S...Any chance of actual pictures Scott?  Thanks Mad Dog 🐕 

hot_rod

Does it have a multi boiler staging control? That would bring on boilers as the loop temperature drops and one boiler cannot keep up. That could keep the boilers running efficiently, the lowest safe return temperature via sensor input.

Multi boilers hybrid piping would have two mod cons and two conventional boilers, the conventional boilers kick in once the mod cons run up out of condensing mode. No need to run 4 mod cons at high, non condensing conditions.

EBEBRATT-Ed

Ther is a pump on each boiler of course it will work.

I would call this 'series primary secondary" the usual method with multiple boilers is parallel primary secondary at least thats what I would call it.

As the boilers stage on or off they affect the return temp of the boilers that remain running

There is nothing wrong with it if the temps are taken into consideration.

hot_rod

My first choice would be a hydraulic sep in the middle. This shows parallel piping for the boilers and loads as @EBEBRATT-Ed mentioned.
And hybrid boiler combination.

RayWohlfarth

I have used this piping on many buildings as a retrofit and had success. The only issue I have seen is the firing sequence. If B1 is the lead boiler, it will be more efficient than B2 because the incoming water to B2 and the sequencial boilers will be warmer than the water to B1. For best efficiency, have B4 as the lead boiler then B3, B2 The efficiency difference is minimal You could equalize the efficiency my using a manifold primary secondary.

GroundUp

This is a pretty common piping arrangement in my parts. B-1 always rots out first due to condensation from taking the load on every call, as 2-3-4 will see sequentially warmer return water. When I do them (regardless of what the engineer/designer draws me), they get piped as Ray shows above. That way they can all see the same temps and maximize efficiency while having no effect on one another.

mattmia2

Seems like rotation would be a good idea. I don't see how it matters what sequence you add additional calls in, the boiler downstream of each firing boiler will always be less efficient by the number of upstream boilers. Am I missing something?

EBEBRATT-Ed

I have seen with Scotts set up on boilers that sometimes when only one boiler runs the others suffer flue gas condensation if piped into a common flue. The off boilers are cold and warm flue gas from the operating boilers causes flue gas condensation in the non-operating boilers.

hot_rod

I think the tekmar 294 manages all the run times, return temperature monitoring ,etc
It can be managed via an app also

Im not sure how you could run multiple boilers efficiently or safely without a staging control?

If a boiler is bring destroyed by low return , that needs to be managed by a return protection device, valve or control

RayWohlfarth

@mattmia2 Here is the temperature rise

EdTheHeaterMan

RayWohlfarth said:

@mattmia2 Here is the temperature rise

Where do you get that Magic Circulator pump Ray?


When I first looked at this diagram my first thought was that there is a better way.
Then I thought like Ray that it may still work but as each of the other three boilers add to the primary loop the law of diminishing returns would make each additional boiler just a little less effective at adding BTU energy to the primary loop. Unless Ray can tell us where he gets those magic circulators

I’ll check with @hot_rod to see if Caleffi stocks them.

Here is a close up of the circulators Ray has designed

This is a lame comedy attempt at Rays Expense. I hope he has a sense of humor.

hot_rod

The load is in charge of the operating conditions of the boilers, always🫢

So  you can put whatever numbers you want in a drawing, doesn’t guarantee the boiler will operate at that condition, maybe ever.

unless you have a temperature responsive control driving a device that can modulate something. A valve, a pump for example. Maybe a magic pump as Ray eludes to?

I would only constrain a delta tee across a boiler to protect it.  Let it run 30delta under high load if needed,even if it was designed for a 20 delta, let the delta adjust to what the load needs.  The delta is the indication of the energy being moved into the system. Or out of.

I agree the temperatures to sequenced boilers will be lower when piped in series, regardless of a primary loop

mattmia2

As the load increases either the delta t will increase or the flow will increase (probably the flow as zone valves out in the system open) so the issue with the last boiler seeing a lower return temp will be less of an issue than if you just assign a fixed delta t to each boiler, either the first boiler will see a much lower return temp under full load or more likely there will be more flow in the loop. In any case I don't see what order you fire them in making a difference in what return temp they see, just randomly pick one then randomly pick another if you need more power to cover the load.

ScottSecor

Sorry for the delay in responding and offering more details.

The existing boilers are 18 years old, not condensing, but direct vent, with a five to one turn-down ratio, natural gas. The existing controller is a Heat Timer Multi-Mod. There are many zones and a large system bypass about twenty feet downstream of the outlet of the base mounted pump.


This is a new account for me. The director of maintenance has been there for about twenty years. He claims this past winter all four boilers were down for some reason during the only cold snap we had here in NJ. When they got the system running it was the first time he ever saw all four boilers fire at the same time. I'm guessing it was raining inside the boilers.

The pairs of 6" x 3" tees for the boilers are spaced at roughly twenty inches on center, and each pair is about 36" from the next pair. As Ray stated, I suspect B1 was doing most of the work, most of the time. All four boilers appear to be in fair condition, although I have not seen the internals. The engineer specified new, nearly identical but condensing boilers and wants my opinion on the piping. We almost always follow what Ray sketched (and every manufacturer I can think of for the past twenty five years or so). As a matter of fact, we have designed many multiple boiler systems with the help of my old trustee Weil McLain 'multiple boiler' guide. I suspect we will be installing the new boilers almost exactly the same as the existing boilers (not my call on this job).

hot_rod

Staging for mod cons works a bit different. Cold return in not a problem, and actually desired for condensing. So the condensing staging controls try to keep boilers running as low as [possible and keep ramping in and out to accomplish this.
Boiler rotation for equal run time.

Modern Hydronic Heating has an excellent section on piping and controlling multiple boilers, standard, condensing, and hybrid.

Might be worth passing that along to the super or engineer. If they want to maximize the new boiler efficiency and longevity. as well As well as comfort.

Might want top pass along this info to the super or design engineer.

If there are ECMs circs involved, now or later, a mag sep is a must.
Or a Sep 4

EdTheHeaterMan

hot_rod said:

The load is in charge of the operating conditions of the boilers, always🫢

So  you can put whatever numbers you want in a drawing, doesn’t guarantee the boiler will operate at that condition, maybe ever.

I know that but I still think the Magic Circulator Pumps are an interesting idea. Besides everyone known that if you put the arrows and the temperatures on the inside of the pipes, there is a better chance of that water knowing what it should do!

EBEBRATT-Ed

@EdTheHeaterMan

I think @RayWohlfarth kept the same drawing as the original and didn't change the boiler in and out temps. I think he did the mixing calculation and put his own numbers in,

The water temp along the main changes the boiler outlet temp because it's mixed with a portion of the return water coming down the main.

I have not done the mixing calc yet myself.

hot_rod

I think many of the mod con boilers have staging function built into the control

With a system sensor down stream if the separator the boilers would modulate on an outdoor reset curve

More  and more variable speed boiler pumps being used, so those modulate with the firing rate

 Variable flow, variable temperature makes the mixed temperature formula a challenge to use

The boilers onboard sensors feed all the data to the control fir sequencing and rotating 

RayWohlfarth

@EBEBRATT-Ed I did just put in some numbers off the top of my head.
@EdTheHeaterMan Hey its called writers liberty to fudge my numbers LOL

EdTheHeaterMan

You know that 86.3% of all statistics are made up with no actual research

That is a fact.

Although I have no research to back that up.

Mad Dog_2

"There are Lies...Damned Lies..and  then...there are statistics!"  Prof.Pacileo, Nassau CC...1991.  Mad Dog 🐕 

jumper

When replacing big boiler in the seventies with multiple babies the babies each came with OEM circulators. When baby boiler is off so is its circ. Hopefully the unpowered circ inhibits flow through unfired boiler?
Vendors suggested tees but I preferred special fittings like monoflows six inches apart. Primary secondary is usually a mistake, unless there's an intelligent control on bypass.

Owners were pleased.

BTW this is how I recommend installing a modern boiler on gravity system. Replace old boiler with big low resistance pipe and tee in to it the new boiler with its smaller connections. Best to install circulator on output of boiler.