Is it possible?

Unknown

This is not in regards to Mike. That stands for Bad Science. If this were true Slant-Fin would have an epidemic on their hands. Personally I don’t think old Slant-Fin is worried. We have not found the root cause period.

Unknown

I have a

HW boiler with 5 zones, not P/S (ramming water through), boiler is sized OK for design day load, but still never gets the rads hot enough as it approaches that date. I see no evidence of condensate on the floor.
Is it possible for too much water to flow through the boiler to pick-up the heat?
I`m planning on adding an ESBE TV valve & going P/S piping.
Thanks

Dave

Steamhead (in transit)

Yes it is

not common, but possible. What type of zones, and what circ?

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Unknown

Thank You Frank,

I thought that,, they were S25`s, but I changed to 15-58`s(and it was gravity). I read your article old friend, and heeded your advice, Thanks for confirming!

Dave

Tony_23

No

The water will pick up the heat, no matter the flow rate. If the emitters are taking the heat off as fast as the boiler produces it, the temp won't come up. If the water didn't pick up the heat it would have to be going up the chimney and your stack temp would be way high. The only thing that happens with an overly fast flow rate is a narrow deltaT.

Unknown

Thanks Tony,

it was a quick call , and I will check tomorrow.
As I said, everything points to the boiler being the right size.
Just crappy piping.

Dave

Steamhead (in transit)

Sure it's counter-intuitive

but I have seen it happen. Sometimes the boiler misbehaves as you say, other times it just hits high limit sooner. But I have solved some mysterious problems by correcting the flow rate, especially on converted gravity systems that are way too easy to over-pump.

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Unknown

Now, Now,

don`t argue boys! Tony makes a good point,, but I gotta admit I`m leaning towards Frank`s scenario.

Dave

Unknown

Simply No

To the water will not pick up the heat. Other conditions are at fault.

Dan Foley

No

Higher flow rate = higher rate of heat transfer.

Here is an article from Siggy that explains it better than I can:

http://www.pmmag.com/Articles/Column/de452c49e3fc7010VgnVCM100000f932a8c0____


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Mark Eatherton

I think the universal answer applies....

it DEPENDS!


In Franks case, with say an older solid fuel appliance that has been converted to oil or gas, and from gravity to forced circulation, then the answer is yes, you can move the water through the appliance too fast, and consequently, more heat goes up the flue than into the water. Remember, the water ways through a gravity boiler were meant to enhance gravity circulation. Throw a pump at it and the flow dynamics change completely.

In Tony's case, assuming a newer, close quarters water way, then no, you can't move the water through the appliance too fast, short of creating hydrolysis or cavitation. If this is the case (small water ways) I suspect you will find another underlying problem, i.e. flue gasses passing through the boiler too fast (missing or pulled baffles) fouled heat exchange surfaces (its AMAZING the R value of soot/carbon) or possibly just simply under fired.

Do a combustion analysis. If it is a problem of heat transfer, it should show. I'd also clock the meter, if it is gas, and see how close it is to spec.

ME

Unknown

Nope

You add a pump to a gravity unit and you will have more heat transfer not less.

Mark Eatherton

Really??

That might be true of a heat emmitter, but based on Franks findings in the field with solid fuel converted appliances, it is not true.

How would one explain that? Fluke?

Remember, the water passage ways in an old ARCO boiler are HUGE (2 to 3" water ways), and water being like my ex-brother in law, is wet lazy and stupid... It just wants to follow the path of least resistance, which is NOT necessarily the path WE want it to flow.

Let me whip you up a drawing to show my point...

ME

Mark Hunt_6

One point being over looked here


There is a difference between emitters and boilers.

Emitters do not care about delta t, all they care about is water temperature.

Boilers on the other hand DO care about delta t. First law of thermal dynamics, heat goes to cold. The greater the difference, the faster the transfer.

Siggy is 100% correct. If we lower the Dt to 10 from 20, the average water temp the convectors see is higher thus increasing their heat output. But the thermal efficiency of the boiler is compromised since we have a higher return water temp.

If greater flow always equaled greater output, why did we install flow restrictors on tankless coils?

Why is there a flow limit on instantaneous water heaters?

Which will cause a burn? Moving your hand quickly through a flame or holding your hand in a flame?

One last thing. BTU output per linear foot of BB is also dependent on the air temp entering the BB, not just the entering water temp. 180 degree water entering BB that has 65 degree entering air will result in higher BTU/Ft output than that of BB with 180 degree entering water and 75 degree entering air.

Mark H

Mark Eatherton

My minds eye on paper

Can you see my point now??

ME

Steamhead (in transit)

ME says

"(the water)just wants to follow the path of least resistance, which is NOT necessarily the path WE want it to flow". How true.

I've never said flow patterns didn't play a part in this. Nor have I doubted Professor Siegenthaler and others who are quoted on the subject.

But flow patterns are partially dependent on the speed (velocity) of the fluid (water in this case) which varies with the ΔP that produces the flow. Next time you run into a hot-water radiator connected supply on top and return on bottom of the same end, jack up the rate of circulation and watch the hot water short-circuit thru the first several sections. I've seen the same thing in radiators that are connected bottom-and-bottom on opposite ends. The water just flows along the bottom, not diffusing to the top until the circ stops. This happens a lot on converted gravity systems, since the piping has so little resistance.

Think about it: how many cast-iron boilers are out there- including current models- that have the supply and return tappings in the same section with little or no baffling such as having to flow around the firebox? What happens when these are over-pumped?

And how about cases where the boiler's flow rate must be different from that of the rest of the system, as with some mod-cons? The answer to this, of course, is primary-secondary pumping and piping with circs optimized to their tasks.

The bottom line is, as many have said, you have to consider the system as a SYSTEM... not just a collection of parts. See how the flow rate affects the SYSTEM.

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Unknown

Thanks guys!

The boiler is a S/F GG125 st. pilot adapted to the old gravity headers & zoned w/5 pumps on the return.(Not installed by me!)
What Frank and Mark mention is exactly what I suspected going-on(F&R tappings on 1 side).
As I mentioned, it works fine when mild,,, but when a design-day approaches it can barely get over 100F.
First thing I thought "undersized",, but a HL calc squashed that idea!

BTW- Great drawing Mark.(My apologies for picking-on you earlier).

Thanks loads for everyones input.

Dave

Mark Eatherton

No problem Dave.

We're all here to either learn, or help or both. I've learned from your posts many times before. Thanks.

In your case (GG 225) those water ways are tight, so increasing flow should theoretically increase the efficiency and delivery of heat from the appliance to the water. So, I suspect there is another cause of the slipping clutch syndrome.

The one scenario I didn't address is excess air in the combustion process. If you have an exceptionally high chimney, when it gets real cold outside, the chimney may be drawing hard enough to the point that the draft relief hood (integral) can't really do a good job of relieving excess air being drawn through the static combustion process and consequently, the flue gasses are passing through the boiler sections so quickly that they can't transfer heat adequately. The solution would be to block the draft inlet off with sheet metal, and install and adjust a barometric damper. Don't forget to install a manual reset roll out switch at the baro damper.

In any case, there is an obvious condition causing the clutch to slip, and I have every confidence you will find it and fix it.

After looking at an exploded view of the GG boiler (http://www.slantfin.com/documents/55.pdf,) I see what you're talking about in regards to the boiler being tapped in and out on one side, and by gully, you could very well be on to something. I've always though that was a silly design, what with water being wet, lazy and stupid...

If you check all the other parameters (input, draft, combustion efficiency) and you've still got a problem, you could be right. Too much flow.

Maybe Noel Murdough will sign in and comment. He used to work for S/F.

Upward and onward my friend.

ME

Unknown

Mark, you bring up a lot of good points. Although the excess pumping may cause different flow patterns in the boiler, the inability to raise the water temperature to over 100F is probably caused by different factors.

It really seems that heat is being removed from the boiler as fast as it can be produced in this case. Mark mentions problems like excess air, or problems with the flow of flue gas throuh the boiler, causing an inability of heat transfer. A combustion efficiency check should easily confirm these conditions with the findings of high O2 content or high stack temperatures. If indeed the combustion reading are normal, then it really sounds like there is more radiation than the boiler is able to handle, thereby removing all the available heat from the boiler at a water temperature of only 100F. The other possibility is that the boiler is severely underfired and there just isn't enough heat being generated.

In the end, there are really only two places for the heat energy generated by combustion to go. Either it goes into the circulating water and into the radiators, or it goes up the flue.

[Deleted User]

Remember...

This boiler was designed for steam and adapted to water. Steam does not care if it leaves the boiler left, right or center. Water does.

If left to natural (gravity) circulation, it probably doesn't make a big difference. But under forced circulation, the dynamics of flow through the boiler do change.

ME

Unknown

OK Mark,

Lets say that the pumping causes bypassed flow in the boiler, leaving some parts of the exchanger with reduced flow. In these underflowed areas, having similar exposure to combustion gasses, these areas consequently operate at higher temperatures. But there is a limit to how hot these areas of the exchanger can get since they cannot rise higher in temperature than the boiling point of water at the corresponding operating pressure.

So even in this limiting case, the heat excanger "hot spots" cannot rise to more than 260F or so under normal conditions. While these areas of the exchanger may be operating at slightly less efficiency, it still would not explain such a great loss of efficiency in heat transfer.

Unknown

Slant-Fin

Galaxy GG Series boilers are designed specifically for hot water heating systems. For other requirements, including tankless coils for domestic water, steam heating systems and low profile steam models, refer to the Galaxy GX-GXH-GXHA Series boilers. Altogether, there are 85 Galaxy boiler models in a variety of sizes and configurations to meet most heating requirements.

Unknown

Just heading

there now to do some more testing.
BTW rw- You seem quite knowledgeable on Slant/Fin,, do you work there?

Here`s a PDF of the unit showing only 3 pumps right now.

Dave

Andrew Hagen_4

Pumps

Obviously that system either has extremely restrictive heating loops or it is way over-pumped. My guess is there is way too much pump there. Are there check valves on the pump discharges? If there are, are they working? You could be pulling backward through the other two zones when one is calling. Looks like one circ is already a 3-speed UPS15-42F, but it has no internal check valve, unless there are check valves in the piping above.

I would replace all three with Grundfos 3-speed 15-58's with internal check valves and do a repipe as quickly as possible to provide boiler protection.

Flow rate and temperature rise/drop are directly related. if you over-pump, the emitters have a higher average temperature and a lower temperature drop. The higher average temperature means at a higher flow rate they have more output. The opposite is true with the boiler. As the flow rate increases, the temperature rise decreases. The effect is that the boiler has to raise the temperature of the entire heating loop and the water inside the boiler at the same time. If the boiler is large enough, this should not deliver significantly different performance than the proper flow rate. Obviously, there may be specific boiler designs that are not compatible with higher flow rates. Your boiler is not one of those.

Unknown

Boiler vs. Load And No

If you have 3 circs and they only move 3 gpm per zone @ a 20*F delta T that = 90,000 BTU's. Your boiler has 90,000 BTU's to give. 5 circulators would give you a lazy 1.8 gpm per zone. Not alot of water moving, but enough for only 90,000 BTU's. The root cause is either A) Too small a boiler, or Too big of connected load.

Mark Eatherton

What's to limit the flow to 3 gpm?

And how many times have YOU seen a 20 degree DT?

THose look like some pretty serious pumps to me.:-)

Just curious...

ME

JasonB

This is simple. The btu input is always the same so the variable is flow. Do we put less btu's in more gallons or more btu's in less gallons. The latter will produce higher water temperatures in lesser gallons.
Just add a boiler bypass and get hotter water to mix with the bypass water and the water temperature will get hotter in the system, as the outside temperature drops. If the outside temperature warms up less system water temperature. It's called following the piping diagrams from most of the cast iron boiler manufacturers. Large water volume use a boiler bypass. I have many boilers I have done this with and the fuel bills drop and comfort levels go up. The radiators are a different temperature as the outside temperatures change. Just do the math and it will tell you what the delta T needs to be in the boiler to heat well. Normally 40º delta T through the boiler will work. Remember a boiler bypass passes cold return to hot supply, therefor the full sized bypass valve is wide open and the flow through the boiler is reduced with the boiler valve.

Unknown

Nope

If that were true we would only need 1 size of boiler for all jobs. If the boiler does no produce enough power the by-pass is irrelevant.

Unknown

ME

What limits the flow to 3gpm. Just a guess with a couple of low head pumps and some 3/4" pipe out in the system hiding.
20*F it's just a figure, he did mention at or near a design degree day application so the boiler would only need 9gpm.

Mark Eatherton

Well that's interesting....

Because the very first part of their "GALAXY" I&O manual, and 83% of their pages are dedicated to STEAM, not hot water...

And when you look at the parts breakdown for the two, the blocks look identical, except the steamer has a place to put a coil in the side, but both first section castings are HUGE, wide open spaces.

How would one know...

You didn't answer Dave's question, do you work for Slant Fin?

Just curious.

ME

Unknown

A few guys

seemed to have missed my 2nd posting,, I DID replace those huge pumps with 15-58s W/CVs. I took those pics awhile back.
The customer IS going to have me re-pipe this properly, but I was bewildered about the water temp.
I did a HL, but the #s did NOT add-up to a too small boiler.

Anyway,, today I found a big part of the problem,, the cust. had the gas utility perform their test procedure 3 months ago, so I passed on doing my own,,,,,WRONG!!!
My tests revealed a grossly underfired unit at the manifold.
Tweaked-up the main GV reg & clocked the meter, so now the units firing right-on, what a diff!
Believe me,, I`ll NOT make that mistake again!

Dave

Unknown

Root Cause

What was the prior gas pressure vs. current gas pressure? A slide rule will give you the cfm change.

Steamhead (in transit)

Bottom line is

you found the problem, and the system as a whole (the SYSTEM!) will perform better than it ever has. Nice going.



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Mark Eatherton

Good job Dave...

and NEVER trust a utility ;-)

Glad you got it figured out.

NEXT...

ME

Mark Eatherton

Mike....

Agreed, something has to give. I'm thinking that those sections not flowing real well are running at a higher temperature, but obviously, so are their flue gas channels, and they are hitting a point of thermal equalibrium. Kinda like thermal constipation :-)

I dunno, maybe I'm all wet, but when I see a cut away of the first casting and it has a HUGE, WIDE OPEN water way running through it, one just HAS to think that there is going to more flow through that section than there would be through the tighter sections. Obviously, no one who knows for sure wants to talk about it, so I guess we'll all stay in the dark :-)

One of these days, I will take one of the cast iron boilers I have up at the college, and put a flow meter on the water side, and a gas meter on the fire side, and a combustion analyzer on the flue gas side and see how close the REAL numbers line up with the theoretical ones...

ME

Unknown

Just a notation

If you started out will approximately 1.75” wc on the boiler and boosted it to 3.5” wc which would be double the gas pressure your boiler’s actual fuel burn increased by approximately 30%.

In this case it equals a gain of 30,000 BTU’s. If we throw out 1 gpm for external boiler losses and stick with our 9 gpm going to the heat emitters @ 3 gpm per zone “on paper design gotta love that” we picked up 10,000 BTU’s per zone.

Charlie from wmass

Dave a good lesson learned. Never believe what you are told. Say thanks for the info and test for yourself. Be polite and even if you test 1000 times and find them to be the same do not accept them the 1001 st time. This goes for the statement "Yes the electricity is turned off!!"