coyote vs road runner application

norfitz

A military base spec'd and ordered an expensive 30 PSI boiler to serve a control tower. The boiler is at the foot of a 90' water column. The engineers proposed pumping up from the mechanical room, through check valves, and on the return, as it enters the boiler room, installing a big pressure reducing valve sized properly for a low pressure drop and set to 20-22 PSI. This somehow reminds me of Road Runner painting a doorway on a rock wall and running through it, and Coyote tries but splats into hard rock. Might this be so crazy it might work?

Gordan

Is that the boiler rating or the T&PRV rating?

It's easy enough to put a 50 PSI relief valve on there...

Gordan

As to crazy enough to work...

I can't see how. Something has to force the water up, which means that it has to overcome the static pressure, which means that it has to be greater than the static pressure. Check valves could maintain a pressure differential in the reverse direction but can't create it in the forward direction, otherwise we'd just have check valves and no circulators.

Zman

Only for the roadrunner...

That won't work. The easiest would be if you can increase the relief valve size. If not just do a heat exchanger.

Carl

EBEBRATT-Ed

no way no how

Sounds like they are trying to rewrite physics. Put the boiler up top or use a heat exchanger as Carl said. It's the only way.

Zman

The military

Ok,

I think you actually could do it. It is however an idea that could only be dreamed up by the military. If you sized a pressure reducer with a big enough spring and enough capacity, I am thinking could use it to support the weight of some of the water.

Overall the pressure at the 90' column will 39 psi (that new conversion table sure is handy). If you are shooting for 22 psi at the boiler you need to hold back 17 psi. I see 2 major problems with the plan. First, you circulator will have to overcome the additional 17 psi plus the head loss of the check valve, pressure reducer and the regular system loss. It will cost more to buy and run than either of the other solutions. Second, If either the check valve or the PRV fails, you boiler room will be flooded with very hot water and the heat won't work.

Thank you for the most interesting puzzle,

Carl

nicholas bonham-carter

Purpose of the hot water?

What is the hot water being used for up in the tower?

Maybe the boiler should be supplying steam to the top, and then a heat exchanger up there would give them hot water.

It's amazing that we have been as successful as we have considering these various stories of "military engineering"!--NBC

icesailor

Flow:

Not so.

Closed loop heating systems on multi-floor systems are like Ferris wheels. The opposite weights on either side of  pump is equal. What is "pushed" up, is "pulled" down. The operator of a Ferris wheel will try to always have riders spaced on the wheel so that it is in balance and the engine does not have to use excessive energy to push on the upside because it will free wheel on the down side. There is no "pumping up" in a heating system. Only in plumbing when the fluid is lost through a faucet.

If you take a coil of 1 1/2" PEX pipe and made a round loop, 100' in diameter, laid it down in a horizontal plane, put a pump at some point and pumped it, the only pressure required to circulate the water is what is required to overcome the resistance of the piping. If you flipped the loop into the vertical position, the pressure requirement doesn't change, only the total pressure on the loop at the bottom.

"Head" pumping pressure in  heating system isn't the same as "pumping" head pressure in a domestic water distribution system. There, you need enough pressure to get the fluid to the top floor with enough pressure to have serviceable pressure and flow out of a faucet.

Head pressure on a heating circulator on a closed loop heating system has nothing to do with the ability of the pump to "push" water up. It relates to the ability of the pump to overcome the resistance of the piping in the loop.

No mater where you install the pump in a closed loop, when the pump is at rest, the pressure on the pump is equal on either side of the pump, regardless if it is on the supply or return side. Put it half way up on the loop. The pressure will do down but it will still be equal. When you start the pump, the differential between the inlet and outlet of the pump will be the pumping head pressure. If the static/rest pressure on the pump is 5# out and 5# in, it is said that it is a 10# head. No matter where you put the pump, when the pump is running, it should stay at 10#.

icesailor

Flow:

Not so.

Closed loop heating systems on multi-floor systems are like Ferris wheels. The opposite weights on either side of  pump is equal. What is "pushed" up, is "pulled" down. The operator of a Ferris wheel will try to always have riders spaced on the wheel so that it is in balance and the engine does not have to use excessive energy to push on the upside because it will free wheel on the down side. There is no "pumping up" in a heating system. Only in plumbing when the fluid is lost through a faucet.

If you take a coil of 1 1/2" PEX pipe and made a round loop, 100' in diameter, laid it down in a horizontal plane, put a pump at some point and pumped it, the only pressure required to circulate the water is what is required to overcome the resistance of the piping. If you flipped the loop into the vertical position, the pressure requirement doesn't change, only the total pressure on the loop at the bottom.

"Head" pumping pressure in  heating system isn't the same as "pumping" head pressure in a domestic water distribution system. There, you need enough pressure to get the fluid to the top floor with enough pressure to have serviceable pressure and flow out of a faucet.

Head pressure on a heating circulator on a closed loop heating system has nothing to do with the ability of the pump to "push" water up. It relates to the ability of the pump to overcome the resistance of the piping in the loop.

No mater where you install the pump in a closed loop, when the pump is at rest, the pressure on the pump is equal on either side of the pump, regardless if it is on the supply or return side. Put it half way up on the loop. The pressure will do down but it will still be equal. When you start the pump, the differential between the inlet and outlet of the pump will be the pumping head pressure. If the static/rest pressure on the pump is 5# out and 5# in, it is said that it is a 10# head. No matter where you put the pump, when the pump is running, it should stay at 10#.

Gordan

I was thinking about it last night

(Yeah, I know?)



And I came to the same conclusion: in essence, it would work like a drainback system only without draining back. Theoretically. But boy. What a beauty.

Gordan

Well...

You don't account for the the need to maintain the pressure differential between the two "zones" (the low-pressure boiler "zone" and the high pressure system "zone") in your thinking. See Carl's explanation. Upon further thinking, I do think that it could "work" with a very high head circulator on one end and the PRV on the other, but it would be no Ferris wheel I'd ever want to ride on.

Mark Eatherton

I am curious Chris...

What effect does the PONPC have on your theory?



What happens if the expansion tank is connected to the INlet of the pump?



What happens if the expansion tank is connected to the OUTlet of the pump?



Everything else in your explanation looks good...



ME

Mark Eatherton

Sounds like someone in the Army screwed up...

Oh, wait a minute. I forgot. The Army Corp of Engineers doesn't make mistakes. They make "Change Orders".



If the boiler can't be fitted with a higher relief valve setting, the change order should read "Move boiler up into the tower and install on exterior wall, venting through the wall. Run appropriately sized gas line, and drain line", or "Place ASME rated heat exchanger to isolate low pressure water from high pressure water, pump accordingly"



What they are trying to do will be very problematic as it pertains to entrained air. It would be cheaper and more efficient to, as others have said, set a heat exchanger.



There are a LOT of electronics in the typical control tower. I'd question wether they even NEED heat. At most, heated windows for human comfort... and probably need more heat rejecting than injection...



Did they do a heat loss/gain calculation?



Leave it to the government to try and reinvent what mother nature has established since the beginning of life...



ME

Gordan

That's what they SHOULD do

But when egos go bad, often more effort is spent justifying what they did lest they have to admit to a mistake, than actually justifying the high ego by doing things right.



One way to mitigate this disaster somewhat, if they insisted on doing it wrong, would be to pipe the boiler pri-sec, put the PRV on the return boiler riser, put the circulator and the check valve on the supply boiler riser, and put an oversized expansion tank at the inlet of the boiler circulator to smooth out the static pressure bouncing that would surely occur. Oh, and put isolation flanges on the circulator so they can easily replace it when it's prematurely destroyed, because it is sure to cavitate until it can spin up enough to overcome the static pressure differential between the two "zones" and pop the check valve.

Ironman

"Sounds like someone in the Army screwed up..."

"Oh, wait a minute. I forgot. The Army Corp of Engineers doesn't make mistakes. They make 'Change Orders'."



Still laughing about that one. I was thinking the same thing. The only difference would be that I would say: "Engineers don't make mistakes". Adding the force of authority (a military commission) makes it more impossible. Some will catch that.



And, I agree. As much as this sounds like blasphemy, this job doesn't sound like a good candidate for a hydronic system. As some form of a/c must certainly be necessary, why not ductless heat pumps. A VRF system, like Mitshubishi's City Multi, could save a lot of energy $$$.



Oh, wait. That's not the way the Fed. operates. They're supposed to take our money and spend it, not save it. My bad.

norfitz

...but not on an ASME 30 PSI boiler

...but not on an ASME 30 PSI boiler

norfitz

brazed plate HX

Yes, adding a big brazed plate HX would be a sure fix

norfitz

yes!

Yes, dreamed up by the military because somebody ordered a 30 PSI boiler. There's a disconnect between engineering and purchasing, so this type of thing must happen all the time

norfitz

space heating

space heating

norfitz

Ha Ha.

Thanks everybody, for your science, suggestions and snark. Meep Meep.

jumper

I don't understand

The proposal sounds so dumb to me that I must be missing something. Why not use a higher pressure water heater ? Why not locate the boiler higher ?



And yes it will work but the circulator will work harder. It has to boost pressure between ninety feet and the reduced pressure supplied by PRV. Plus when the PRV drifts from its set point, and they always do, either the relief goes off or the pump performance goes off spec. If that deviance from spec lowers the flow below what the boiler requires......

Larry Weingarten

Wierd idea

How about moving the boiler up towards the top of the building, so it runs at the pressure it should?  Piping lower down can take 90 psi without problems. This is a Henry Gifford idea. 



Yours,  Larry

Harvey Ramer

That might work.

 If I am correct on this, a PRV won't let water through until it sees a pressure drop downstream reguardless of what the pressure might be behind it. If you had an expansion tank on the inlet of the circulator it would have to pump it dry before it could create a drop across the boiler to the outlet of the PRV. The expansion tank should go on the outlet of the circulator before the check valve.



Not saying this is a good way to do it. Just exploring possibilities. It would still be a humdinger to keep air out of the system.

tim smith

Engineers I think screwed the pooch.

 Them coming up with the wild idea of using a prv on return is weird at best.  Just do a  flat plate and be done with it.  Or, ship the boiler back and get a 75 psi condensing boiler? 

norfitz

most of you are right

Yes, buying another boiler, converting to primary/secondary with a HX or putting the boiler at the top of the system are all smart effective solutions, but I heard that the engineers were considering the Road Runner/Wily Coyote solution and had a scientific curiosity about whether it could work.