Settle a bet (How water circulates through radiators)


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Old 01-10-08, 07:18 PM
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Settle a bet (How water circulates through radiators)

Can any of you settle a bet?

Our building has hot water boilers with old-fashioned cast iron radiators. There is one 3” heat supply pipe that runs around the perimeter of the building and all the radiators tap into this pipe. We’ve been debating how water circulates through the radiators since the main supply pipe basically bypasses the radiators. Two of us say the hot water flows through the radiator because there is a pressure differential between the radiator inlet and the outlet. The radiator inlet pipe would have slightly higher pressure than the outlet pipe because of pump action. The other guys say the water is following the path of least resistance past the radiator pipes and the heat is coming into the radiator by convection.

Who’s right?
 
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Old 01-10-08, 07:49 PM
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Could you take a picture of the tee fittings?
 
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Old 01-10-08, 08:12 PM
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I assume you mean the fittings coming off the main supply pipe.

The radiator feed pipes are 3/4" (or thereabout) cast iron pipes that are welded into the main 3" supply pipe at a 90 degree angle to the main and about 4 feet apart. There are no other controls at the junction of the pipes and there is no proportioning valve on the main between the radiator inlet and outlet pipes. It's just two smaller pipes welded into a large pipe. This system was installed in the 1920's and was originally high pressure steam. The radiators have the usual shutoff valve on the inlet side and a bleeder valve on top.
 
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Old 01-10-08, 08:24 PM
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Well, just an opinion here, so we'll leave it to the experts to resolve the bet. If it is a straight tee fitting then I would say it is simply a matter of hot water being lighter (less density) and rising (convection). The hotter water rises up the supply leg, cools going across the radiator and drops out the other side. Gravity heating off a pumped single pipe...

If my hunch is right then you'd find the the supply goes to the top of each radiator and exits the bottom and never vive-versa.

I doubt it could ever be flowing because of the pressure differential aspect when the easiest path by far would be to not turn and just continue through the 3" main rather than taking the long way through a 3/4" loop that goes a lot farther than 4'. What are you going to owe the other guys?
 
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Old 01-11-08, 06:07 AM
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The inlet is at the bottom of the radiator, and the outlet is at the top of the radiator, if that makes a difference.

One observation seems to contradict the convection theory. When I have an air-locked radiator the whole radiator is cold, even though it is mostly full of water. Once it's bled down I can feel the radiator quickly getting warmer beginning at the inlet and moving toward the outlet. It heats up much quicker than I would think convection alone would heat it.

The losers of this bet have to eat a bug.
 
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Old 01-11-08, 06:10 AM
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Still waiting for pictures. You made no mention of a circulator or whether there are TWO pipes,
a 3” heat supply pipe that runs around the perimeter of the building and all the radiators tap into, and maybe a return pipe that is taking the return?

Something has been lost in the translation here. What is described here, if in fact it is ONLY one pipe 3 inches in diameter and only one pipe, and no return pipe from the other side of the radiator, defies the laws of physics, UNLESS it is a MONOFLOW system!

THIS IS WHAT YOU MOST LIKELY HAVE!

Look at the 'TEES" and read what it says on them. They should have an arrow pointing to the direction of water flow through the radiator circuit. Many old buildings use the monoflow system that were originally using steam because it is a one pipe system and easily convertible from steam to hot water.

EVERYBODY hold your loot for now! Maybe we should wait for some pics first!

Give us some pictures of the radiators and some of the boiler and piping INTO and OUT of the boiler.

The remark about "HIGH PRESSURE STEAM" is absolutely wrong. "LOW PRESSURE STEAM" maybe.

Either it has to be TWO pipes, one for in and one for out of the radiators, or a MONOFLOW. Even a gravity system couldn't possibly work as described.

PICTURES please!

Are you still taking bets?

Charlie

(sorry Who but I had to jump in being the passive non-opinionated wuss that I am----hehehehehe---ok pal?)
 

Last edited by boilersrus; 01-11-08 at 06:12 AM. Reason: spelling
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Old 01-11-08, 06:21 AM
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Charlie, monoflo suspicions were the reason I asked for pictures of fittings in my first post.

So go ahead and be a PNOW...

So if those are simple tees, and the rads are piped as you say, it could possibly be pressure differential but only furd could ever imagine the size of the pump! LOL
 
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Old 01-11-08, 07:57 AM
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Your description of a monoflow system seems to be the correct one.

Our system is, indeed, one pipe (not separate supply and return pipes. Both the inlet and outlet pipes from the radiators are welded into that one 3" main pipe with the inlet always on the "pressure" side (closest to the pump). The piping is steel or cast iron and is very rusty so I can see no arrows on the piping.

There is one 10hp centrifugal pump circulating the hot water.

The old steam boilers may have been low pressure. They were replaced before any of us started here so we never saw them. We were told they were HP.

I don't have a digital camera so pictures are a problem. I'll try to borrow one and get some pics tomorrow.

I'm no pyhsics major but my thought is that in order for water to flow in a closed, pressurized pipe, any two points along the pipe would have to have some small pressure difference. Otherwise flow just wouldn't happen. My working theory is that the radiator inlet, being at a very slightly higher pressure than the downstream outlet would make pressure flow possible.

This has turned out to be an interesting thread!
 
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Old 01-11-08, 08:03 AM
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Here is a good read on diverter-tee systems (Monoflo is Bell and Gossett's trade name for these fittings) and how they work...

http://www.heatinghelp.com/heating_howcome3.cfm

If it is simple welded fittings then it isn't a Monoflo system... and mayeb it is that monster sized pump, which if that's the case could be much smaller if there were diverter tee fittings.

Any idea of the difference between the supply and return temperature under normal operating conditions?
 
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Old 01-11-08, 11:13 AM
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OK. Here are some pictures of our setup.

First, the welded stub. both inlet and outlet are the same:


Next, a ceiling radiator showing the hookup. This radiator is on a side circuit so the main pipe is smaller, but it illustrates the point:


A "normal" radiator:


And finally, the circ pumps. These are 20hp instead of 10hp which I said earlier. If memory serves we had about 15psi on the return side of the circ pump. Don't think I ever saw supply side pressure readings. One of the pumps is a backup:


I can't get temperature drop readings since this building is currently shut down cold and may be facing the wrecking ball.

All I can say for a fact is that this setup works fine, apparently without diverters or fancy tee's. I would like to cut open one of the mains and see if there might be some kind of "hood scoop" built into the inlet pipe that would scoop up hot water and send it into the radiator. Unfortunately, that would require real work which I am presently alergic to. LOL

Had a good crawl down some partially flooded access tunnels to get the stub pic. Am I tenacious or what?
 
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Old 01-11-08, 11:18 AM
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roach, good work on the shots...

It's starting to look more and more like they just pumped and pumped until the water would go anywhere...
 
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Old 01-11-08, 07:55 PM
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It would have been ingeniously possible for the pipes welded into the supply loop to have been cut on an angle and facing the direction of flow. It would have been simple to build that way. The return could have been facing the other way or not angled at all. Otherwise, I don't see how it would work on water or steam.

Ken
 
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Old 01-12-08, 06:19 AM
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I know from nothing about steam heat (not much use for it when it's 70 degrees in January), but I was guessing what Ken said. I used to have a chlorine feeder for my pool which was engineered like that.
 
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Old 01-12-08, 10:50 AM
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well, this ay not sound like it applies but fluid dymanics are fluid dynamics and air is considered to be a fluid for this purpose as it acts as any other fluid.

when installing smoke detectors in an air duct, they are mounted on the outside of the duct but air must circulate through the detector for the system to work.

What is done in those situations is, a plain hole into the duct is used for the inlet but in the outlet side, a pipe with several holes in it is placed across the duct with the holes facing downstream of the air flow. The airflow past this tube causes a low pressure in the tube which effectively draws air through the inlet and across the smoke detector in the duct detector.

If a pipe as Kfield suggested was placed in the return pipe, it would cause not only a lower pressure in the return pipe (from the radiator) but it would also cause a restriction in the pipe which would cause pressure on the supply inlet of the radiator which either or both would cause a flow through the radiator.

So roach, since you started this, it is now up to you to answer it. You now are directed to grab a sawsall and chop open a couple of the tee's and let us know the answer.

the one other thing that would cause a same action would be a restrictor placed in the mainline between the supply and return taps.

just a word of notice for everybody.

I am an electrician, not a plumber.
 
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Old 01-12-08, 07:35 PM
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I'd love to take a saw to the pipes and settle this, but I'd then have to repair it and that would be a problem on these old pipes. If the building does get knocked down I'll defenitely give it a go, but until then we'll all have to be left in suspense. The "hood scoop" theory sounds the most plausible. Fortunately, that makes our bet void and no one has to eat a bug!

Thanks everyone for your input!

Da Roach
 
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Old 01-13-08, 07:06 AM
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So monoflow it is gentlemen?

I guess this is probably a FIRST.

A unanimous decision and the winner is: MONOFLOW

WHO: Nobody was disputing or even questioning your suspicion, I was IN AGREEMENT with your suspicion. I just like to E X P A N D it more (aka 'blab more') to the nth degree sometimes. We ALL suspected the monoflow system, but the REAL question was HOW the 'tees' were engineered and just welded in place. ALOT of different ideas, but only a sawzall will reveal the truth!

I personally have never seen this type of system with the 'tees' like they are and learned alot from this thread. I wonder if I was the only 'old dog' to learn something new.

Charlie
 
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Old 01-13-08, 08:09 AM
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Charlie, not quite unanimous and I take no offense to anything except you adding a "W" to the end of Monoflo™. hehe This is an interesting situation and it's too bad that this was all just a mental tease since roach won't do the honorable thing and get a sawzall to hack apart the heating system (although a snake camera could be interesting).

BTW, the convection theory has to be ruled out completely by the photo of the radiator underneath the piping. That's a big heat trap. Even massive excessive pumping probably wouldn't get flow through there. If I stop the flow through any rads under my monoflo main they won't start flowing unless the temperature difference is small enough. Heavy water is hard to move.

Restriction orifices and massive pumps seems the best guess for me. Monoflo to me, means using a venturi effect to induce flow. I don't think this system can be classified that way.
 
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Old 01-13-08, 10:22 AM
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MENTAL TEASE IS CORRECT!!!!!!!!!!

I spelled it correctly the first time I was going to post, but the SPELLLLLLLLCHECKER corrected it to 'MONOFLOW"

Try it and see!

Put 'monoflo' in and hit the spellchecker. "MONOFLOW" comes up.

I wasn't sure, so I went with the checkerrrrrrrrrrrrrrrrr!

Surry if eye spoirled yur diy wid mi bud spilling

CUT THE DARN PIPE OPEN! DO IT FOR US! YEA!

Who: I like how the little TM (trademark) dohicky thingy you put there is done. COOL!

Charlie
 
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Old 01-13-08, 03:03 PM
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Enough with the guilt trip already! I saw a spot where the radiator had been abandoned and the stubs are a straight shot into the pipe. Assuming the pipe is drained in that section I'll try to stick a wire down the stubs and see if the pipe extends into the main. I'm sure that will be the case. Maybe I'll be able to figure out the shape also.

Stay tuned.....
 
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Old 01-13-08, 03:54 PM
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Enough with the guilt trip already!
We're 100% joking about 0% serious about this... nobody expects you in any way shape or form to start ripping up the system. Sorry if it didn't comes across that way...
 
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Old 01-13-08, 07:47 PM
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I will mail you my sawzall tomorrow, ok? Do you think it will fit in an envelope?

We really are curious but I was only kidding about:
CUT THE DARN PIPE OPEN! DO IT FOR US! YEA!

Sorry you took ALL of us so seriously, especially me.

Charlie
 
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Old 01-14-08, 07:57 AM
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I know your comments were all in fun (as were mine). I really am curious about the design of this system so I'm going to try to scope it out non-destructively.

No offense taken guys!
 
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Old 01-14-08, 04:12 PM
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OK, sports fans. I found two radiator stubs that had been capped off. I removed the caps, bent a hook in a piece of wire and shoved it down the pipe, caught the end of the stub where it enters the main pipe and measured the length of the stub all the way around its circumference. I fully expected to find that the stub had been cut at an angle to make our "scoop" but I didn't find that. What I found was apparently a nice, square 90 degree edge all the way around the stub. No bevel extending into the pipe.

According to my (admittedly indirect) measurements it looks like both stubs are cut square where they enter the main. They **might** be recessed into the main pipe but not by much. Maybe 1/4" or so.

I know this isn't what we expected but there it is. That's about as far as I can go with this until the building comes down. Thank you all for sharing your expertise. If I ever get the chance to do some sawzall surgery I'll post it up.
 
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Old 01-15-08, 11:31 PM
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HEY- HEY- HEY----- Don't go yet!

What happened to the 'snake cam"?

Stick the camera down the pipe! We have a bet going on here!

HEY - HEY- ROACH-----The snake cam!
 
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Old 01-16-08, 12:13 AM
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Okay... so now is where xiphias can step in, walk us through the feet of head calculations - they don't have to be too exact for this, just assumer the loop length at 3" diameter... next calculate what the GPMs should be and then examine the pump specs and see what they are. If you pump enough water through...
 
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Old 01-16-08, 11:09 AM
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Sorry, Boilersrus, none of us have ever SEEN a snake cam, much less had access to one. This is a pretty cheap place we work for. If you'd like to mail one over I'd be happy to give it a go!

One thing I noticed is that all the stubs come out of the side of the main. Whether the rad is above or below the main they always come out the side of the main. I have no idea whether this is significant but it's so consistent that it seemed to be designed that way.
 
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Old 01-16-08, 11:50 AM
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Originally Posted by Who
Okay... so now is where xiphias can step in, walk us through the feet of head calculations - they don't have to be too exact for this, just assumer the loop length at 3" diameter... next calculate what the GPMs should be and then examine the pump specs and see what they are. If you pump enough water through...
The answer is 11. The choice of units is up to you!
 
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Old 01-16-08, 02:25 PM
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I'm still working on getting the SNAKE in the envelope!
 
 

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