Anything Wrong With This Drawing?

ced48

Can anybody find something wrong with this piping diagram? Key in on the DHW loop for potential problems. There may, or may not, be something wrong. It is not a trick question or game, I'm just trying to track something down-

Jamie Hall

No valves? I can see the possibility of some annoying phantom flows...

icesailor

Other than the fact that most indirect heaters want the hot to enter from the top and exit from the bottom, it will probably work as bad as any boiler without hydraulic separation.

Its just that there are better ways to pipe it.

Some manufacturer wants it that way and you don't like it? I understand you.

IMO-FWIW

ced48

Jamie-There are swing, or spring, check valves in the DHW, and SH returns. They are those bumps in the lines, they were labeled as such on another version of the drawing. Thanks for taking the time to look for me-

ced48

Ice-Yes, but that's not where I'm going-Like I said, there might not be a problem

hot_rod

I don't like to see bull-headed tees, but if only one pump runs at a time it is fine. I wonder why one side is piped with flow into the tee branch, the other bull headed?

A vertical air separator installed just below the boiler would assure both circuits have the best air elimination, although I believe the tank has a float vent.

Snowmelt

I would have primary / secondary & another air eliminator on the iwh.

unclejohn

There is no problem with that DHW piping.

ced48

Well enough guys have seen this so I will ask a more direct question. Is there any way, indirect pump only running, that the suction from that loop could pull in air thru the micro-bubble air separator? There are IFC valves in both circulators.

hot_rod

Both circs are pumping away from the expansion tank (PONPC). If the system is filled with fluid and pressurized no air can be pulled in from the air vent.

ced48

In my mind, I visualize the water being pulled out of the boiler and the suction trying to pull water from the SH loop, but stopped by the check vale. Couldn't this action possibly pull air in from the separator, either from air already trapped in the top, or down thru the vent? I assume you are right, rod, just trying to get this thing and my brain to come to terms.

hot_rod

Here are the drawings that helped make it clear for me. I believe they are old B&G schematics with some color added and included in Modern Hydronic Heating, 3rd edition, John Siegenthaler.

They shows a typical circuit with a small circ installed. In a closed loop circuit there really isn't a suction, per say. A pressure difference is established by the centrifugal force of the impeller spinning.

The pressure increase above the static fill pressure is "evidence" of "head" energy being added by the circ. Notice the delta p added shows up as an increase in pressure throughout the circuit.

Pipe, fittings, etc in the piping circuit use up or scrub away the added head as the fluid flows around.

Now with a high head circ, for example, capable of a large delta P, pumping towards the PONPC, you could pull sub-atmospheric conditions, lower the boiling temperature, create steam bubbles and induce cavitation. That is sometimes diagnosed as an air problem, knowing the cause is the key.

Under some conditions air could be pulled into the system from a vent that is in the open position, float dropped down for example.

In that boiler piping drawing you posted the two pumps are piped close enough to the PONPC, both or either are "pumping away"
Many of those mod cons have air vents up high in or on the unit, to vent the HX. those need to feel a 5 psi minimum positive pressure to assure a tight shutoff. Fill pressure should assure that, pump may add additional pressure.

ced48

Thank you hot rod for taking the time to post all this information. Your two files won't open for me, so I haven't seen them. So, I guess my "suction" theory is all wet. Are you saying that over pumping could cause problems that might be confused with air issues?

The files are opening now, so I'll take a look-

ced48

After reading again, and looking at the diagrams, I guess you are still saying that everything is fine with this arrangement, because it's pumping away?

unclejohn

Ced48 Only one circ. runs at a time if properly wired. The water is going to leave the boiler go to the DHW tank through the tank and back to the boiler. Case closed. Even if both pumps run at the same time, some water is going to flow through the CH loop and some will flow through the DHW loop.