Primary Secondary Piping?

bert

I've seen this on a much smaller system, and it didn't work well at all, as evidenced by the number of failed boilers laying around. You have 40hp pumps moving water left to right between the system return tee and the separator tee, while you have 3hp pumps trying to move water right to left in the same pipe. Usually the 40hp pumps win, and the result is the boiler side gets no flow at all. Can we say cycling on limit with no place to go?

Dan Hill

Primary Secondary Piping?

If I were to just direct you guys to the attachment, what problems can you immediately point out in the piping drawing without telling you anything else.

Jean-David Beyer

I am not a professional.

1.) No flow-checks at outputs of the pumps.
2.) No closely spaced Ts, so not Primary/Secondary -- unless the Ts between the air separator and the 3hp pumps are meant to be them, in which case they should not have that third T in between them.
3.) Conventional air tank should be hooked above air separator to relpenish the air that dissolves in the water.
4).) Air separator should be closer to the boiler.
5.) The pumps are very big; if this is not a really big system, they are probably way too big.

I hope you did not find this in a real installation? Night school problem? Joke?

Dan Hill

Real system

1) There are triple duty valves and VFD's on all four pumps. Sorry we missed that in the drawing.
2) The air separator is a little further from the boilers then I'd like its but not that far.
3) The system is fairly large. The boiler piping being 6" and the system piping being 8".
4) The header shown on the skid is drawn exactly the way it is piped.
5) I won't disclose where I found this, but it is a B & G factory built skid. And its been in operation for some time. I was just recently shown this install.

Unknown

this is really interesting. frankly I can't tell if there is a problem here or not. the 40's are big, big boys, but if they are pushing relatively equally on the supply and return of the 3's, maybe it's not a problem. the expansion tank... maybe that helps too?

it's an interesting puzzle though. I look forward to seeing more thoughts on this.

Dan Hill

And thats remarkably close to what the building engineer is describing. We were brought into the building to repair building automations systems and while chatting we were asked to take a look at this issue. It hasn't sat right with me since I looked at it which is why I wanted to get some other opinions.

Paul Rohrs_4

Drawing is incomplete

Any way to show us how the supplies and returns connect to the boiler or boilers?

I would consider this incomplete in that you are showing us the zone pumping to, and from a heat emitter, but not where the hot water is originating from (at the boilers).

With those two sets of horsepower pumps, I would consider two different hydraulic separators off of a boiler loop. Flow from a secondary loop will not intefere with flow from another loop if it is piped that way.


Regards,

PR

Jed_2

Do all 4 pumps run?

Do all four pumps run on a call for heat, or are they redundant pumping stations?

Paul Rohrs_7

Clarify

I agree with NRT.Rob, I love these kind of puzzles.

What I should have asked is:

Does the 3hp pumps (shown in parallel) provide supply and return to the boiler(s)?

Then that would leave the 40hp pumps (also shown in parallel) to provide heat (or chilled fluid) to zones.

I don't like the proximity of the expansion tank in relation to the air-separator. I would prefer the expansion tank off of one of the return loops.

Relief valve dumping issues?

Paul

Jean-David Beyer

I was thinking about that drawing...

After thinking about that system, it seems to me that the pump skid is upside down. That is one of the problems. Turning it over would put the expansion at the right height relationship so if the right fittings are used, you might get the removed air to flow into the expansion tank. Unless you actually have a diaphragm type expansion tank and do not need this.

And you gotta take that T out from between the "closely spaced Ts" and move it to the left of where the first pumps to the boiler return pipe is. Then you would have closely spaced Ts (or, at least, you could have if they are 4 pipe diameters apart or less). Then you would eliminate interaction between the boiler circulators and the load circulators.

Jean-David Beyer

I am confused about this quote:

"I don't like the proximity of the expansion tank in relation to the air-separator. I would prefer the expansion tank off of one of the return loops."

If I understand these things correctly, you want the air separator as close to the boiler output (i.e., in the supply line) as possible, because it is when the water is hottest that the air comes our of solution the best.

And if the expansion tank is as it appears, it is a conventional (not diaphragm) type tank, in which case you want a suitable gizmo connected with the air separator so the separated air goes into the expansion tank, so they should be pretty close together, right?

Now if you put the expansion tank in a return loop, where do you put those 40 hp pumps? After the expansion tank, of course, because we pump away, right?

At some point, the pump skid can no longer be used because everything has been changed.

Dan Hill

Clarification

1) The 3 hp pumps supply the two boilers piped in parallel.
2) The expasion tank is actually two diaphram tanks piped one on top of the other off the same 2 1/2" line. They sit on the skid to the left.
3) The air separator is an inline separator on the boiler return.

At least I know I'm not crazy. This system just isn't quite right. I'll have my sister update that drawing a little if we get time tomorrow.

bob_46

Drawing

As long as the 40hp pumps are lead lag I don't see a problem.