School Steam Systems

Owen

Okay, here's one for y'all. How would you figure or find the EDR for a Heat Exchanger?

A big Bell & Gossett shell & tube-bundle: SU-187? Also, would this thing require more than 2-3# steam to work? Along with the rest of a rather large school building complex?

Thanks.



This can be a hell of a lot of fun! What a bunch of

(my wife shakes her head all the time and says " Boilers!")

nerds!

nicholas bonham-carter

Sizing problem

In the absence of any other edr ratings, I think you can come close by sizing it to the diameter of the steam inlet pipe. I am sure the pressure should be lower than 3 psi. Probably the pressure was raised to compensate wrongly for a trap/venting problem.--NBC

bob_46

B&G

http://completewatersystems.com/wp-content/uploads/2011/05/398.pdf

Owen

Thanks!

I looked all over for that very form but for some reason couldn't find it. B&G's website is messed up out this way right now or something.

Anyway, that's what I needed to know. Square foot of heating surface=EDR, right? Duh?

Owen

Reply to NBC Re: Inlet Size

The inlet on this HX is 4". The existing trap is a 2-1/2" Hoffman FT015C-10. According to Hoffman Submittal Form #HS-226(E), this trap can handle 46,000 pounds of condensate per hour at 5# pressure differential, which I'm assuming we have gobs of since the boiler pumps up to 9# back on at 5#. My supervisor changed the pressure on Dec. 9th from what I had it set to (3-5).

Page two of B&G Submittal Form #C-121.7B chart mentioned by Bob above says the tube bundle has 339 square feet of surface area which I am assuming is the same as EDR. 339 divided by 4= 85 pounds per hour. 85#/HR HX with a 46,000#/HR Trap.

I'm missing something here. Anybody care to enlighten me?

furnacefigher15

Yes, missing something

EDR is calculation to determine heat emitted from the steam to the air from a radiator, or pipe.



since this is a heat exchanger, that is transferring heat to water, that changes everything.



339 edr is only 81000 or so btu which is nothing.



In order to reverse engineer that heat exchanger, I would be looking at the waterside piping.



What is the size of the piping used in the main loops of the water side. I would start there, and assume the worst case.



Example 4 inch steel pipe is good for 290 gpm at 4.2' of friction per 100 ft (typical max desired velocity)



At a typical design of 20 degree delta (supply to return on a design day) thats 2,900,000 btu worst case.

Owen

HX Water Side Piping

The HX supply & returns are 6" right at the exchanger. It must reduce down as it extends into the building, obviously, because at the F/C Units the in/out pipes are 1".

I'll have to check on the Delta T tomorrow because everything is on "unoccupied" right now. I don't think, however, that it is anywhere close to 20º. I played around with the AutoMated Logic on a different HX the other day, and if I changed the steam valve to open it more than the 15-20% it was at at the time, the heat in the supply line shot up like a rocket.

You mention 2,900,000 BTU for the HX; you mean that's how much it would need?

The boiler is only 5,500,000 and there are three HX's. Is the boiler undersized?

BTW, how did the engineer who originally sized all this stuff do it? He didn't have to reverse engineer anything; but what parameters did he use? I might be able to find something in the O&M manuals.

furnacefigher15

waterside pumps

Look at the water side pumps, and write down every # you can find, and take note of the piping sizes near the pumps.



Do you run chilled water in the same piping in the summer?



"You mention 2,900,000 BTU for the HX; you mean that's how much it would need?

The boiler is only 5,500,000 and there are three HX's. Is the boiler undersized?"



I mean that's how much it can possibly move, in the example.



The delta t on the waterside will not be 20 degrees at part load conditions.



It is possible, that the heat exchanger is tremendously over-sized.



Is this hx in a building that has a lot heating trouble?



Also, be careful, just because the piping at the hx is 6 inch, does not mean that the main piping is 6 inch.



And if the waterside piping is also used for chilled water in the summer, the flow required is much higher for cooling, then for heating and the piping would be sized for that purpose.

Owen

HX Problems

Everything is B&G.



Closed Loop #1, 1966-1984 East Annex Addn. HX SU-146-2 (Shell & Tube, 14" diameter, 6' long, 2 pass), Year built 1963. 2 Pumps, 1510, 10 HP 1745 RPM, 208-230V 3PH, 28-26 FLA, 86.5 FLEF, 80.2 FLPF; same for #2 pump.



Closed Loop #2, 2005 Audit. & New Gym Addn. HX SU-187-2, Year built 2003. 2 Pumps, 1510, 30 HP, 1775 RPM 91.8 Guar. Eff., 7.4 Max KVAR, 92.4 MEMA Nom Eff, 88.7 FLAMPS, 81 SF Amps.



I measured the feet of head on 3/8/11= 46.5.



The loop piping obviously must reduce down a couple of times because the pipe size at the FC Units is 1"

All piping is 4" at the pumps. No chilled water pumping these loops. The 2005 Addn. has a separate chilled water loop elsewhere in the building.

Owen

Photos

Photo #1, HX #1 Loop #1;

#2, HX #2 Loop # 2 HX & Steam Trap;

#3 HX #1 Loop #1 Pumps;

#4 HX #2 Loop #2 Pumps;

#5 HX #2 Loop #2 HX is leaking, BTW.

Owen

Oops!

Inlet/outlet diameter of # 2 HX (Audit. Addn.) is 6".

It reduces soon after, probably right there at the first or second 90º ells.

furnacefigher15

Here's the pump curve

http://wea-inc.com/bellgossett_series1510_pump.htm



At 46.5 ft of head, that pump will move about a 150 gpm which is good for 1.5 million btu per hour at a standard design delta of 20 degrees.



Do all pumps have 46.5 feet of head? and are the pumps next to each other redundant (only one runs at a time and both connect on same headers)?



If you can measure the feet of head of each loop, you can plot that on a pump curve to see what the actual gpm is.

Owen

Pump Curves

There are 18 of these pumps, from 30HP to 2HP. They are redundant, paired in a lead-lag configuration.

Back in March I did head measurements on all of them and plotted it on the pump curves I got from B&G. I did so because I watched a video tutorial from B&G's "Little Red School House" (kind of ironic). The gentleman who gave the talk demonstrated how you can save a lot of electricity ($) by adjusting the triple duty valves and circuit setters to deliver the design flow and no more. When I started to try it, by throttling TDV's back to match the design, one of them chattered after I left, it alarmed a custodian who told my supervisor; that was the end of that.

So anyway, I've done all that, have the pump curves plotted and there we are. "We've never done that before" kind of thing.

Assuming I could do what needs to be done (I often just do what I think needs to be done without asking, "It's easier to ask forgiveness than permission") what exactly would it be?

SWEI

VFDs

Would be my first thought.  They're far cheaper than they used to be, have more features, and are more reliable.  Start by manually setting the pump speed for the pressure you need, then think about control options going forward.  Most feature built-in PID controllers so even if you don't have a BAS, you can wire a sensor straight to the VFD and maintain constant pressure as zone calls come and go.

Owen

Budget Woes

They say they ain't no money fer that. What ever is is, is has to be cheap or free.

furnacefigher15

The reason

The tripple duty valve chattered is b/c its over sized.



Most people make that mistake. The say to themselves " I got 4 inch pipe, I need a 4'' tripple duty"



The problem is the control point on an oversized tripple duty valve is way down near the off point, and so it will chatter.



The right way would have been to install at most a 3 inch or even a 2 inch. That way the control point would have been a lot closer to wide open, then shut.





Owen,



are you still having trouble heating certain buldings?

Owen

Trouble

Yeah, lot's. Several of the steam systems (seven) and one hot water just don't heat right, have hot/cold spots, etc., etc. Three worked perfectly at two pounds and they got turned up as well as the ones with problems. That's how maintenance is done here, turn up the boiler.

furnacefigher15

Engineering

The way the engineer would have done it was:



1- figure out the heat load of the building room by room, and add all those rooms together, then add a safety factor of some kind (10 to 50%)



2- size the piping to support the safety factor btu amount at a certain delta t, usually 20.



3- Then consult with The heat exchangers manufacturer and provide the desired btu and flow rates and what not to find a hx that will work in the application.



4- Calculate the head requirement of the pump by figuring out the longest run of that pumps loop, and add the head loss of the hx and a safety factor of 50% for valves and fittings



5- Find the pump he needs to fit the gpm at that head, and in many cases use the next size up pump

SWEI

turn up the boiler

How many of those maintenance people have boiler operator papers?

Owen

Papers

Papers? We don't need no stinkin' PAPERS!

We've got a clockwise screwdriver!!

furnacefigher15

I pulled this from the other thread

"I'm having a host of headaches and sleepless nights over problems at the High School. It is 250,000+ sq.ft. including a 1,500 seat auditorium used by the community. That addition, as well as four others, have hot water/steam heat exchangers, three in all, circa '65, '83 & '05. There is in place Automated Logic controls system for online control and monitoring.

This school's boilers are in a stand-alone building which contains one 2008 Weil McLain #94 5,500,000 BTU cast iron sectional boiler and one 1955 Pacific steel boiler which has, sadly, given up the ghost. The WM has surged, primed & had carry-over since early after installation and it has gotten worse since I installed a larger main receiver tank two years ago (275 Gal.). I did not know enough to clean all the pipe after cutting & threading to keep oils out of the water. (I now, of course clean every stick with grease cleaner before installing into the steam/condensate stream.) In addition to the main receiver there are four others at various places in the main original wing. The steam and condensate pipes are of good size having been installed in the mid-fifties when there were still deadmen doing good work. There is about 2300' of main line starting at 8" in the boiler room, reducing down to 3" mostly, with some 2" at one later addition that uses steam. All the other addition wings are hot water/steam shell & tube-bundle heat exchangers."





Did they install the hartford loop and equalizer line?



If are getting wet steam, you will not get good heat output.



The near boiler piping could be your whole problem.

Owen

Hartford, Equalizer & Near Boiler Piping

That's all been done according to Hoyle. Using Dan's "Greening" book and many, many other sourses, I've checked out all seven and they are, more or less as they should be.

This one at the HS is well above and beyond spec. It ain't that.



It is making wet steam, however. SOMETIMES. If it kicks off on LWCO because it's bouncing around so much (needs skimming), and cools down at all, it has been VERY difficult to get it to maintain any pressure and stay running. That was when I had it at 3-5.



There is speculation that demand is creating a "vortex" going up the main risers into the header and sucking water with it. That was reiterated to me by a Hoffan rep also. Too much demand for heat from too many areas at once.

Therefore: MORE PRESSURE! Like filling a bottomless bucket with a vapor!

Except that the heat exchangers (two anyway) are in the damn boiler room! Not fifty feet of pipe away! (The small one, a 6-8" B&G SU is about 600' away.)



What is the answer to that argument?

furnacefigher15

Owen

I am confused.



How many boiler systems are we talking about. It would be best to focus on one system at a time. I was under the impression there was one heating plant, that fed everything, but you have confused me by saying 7 steam systems. Does that mean 7 isolated team systems, each with there own heating plant?



Can you take pictures of the boiler / boilers

Owen

School Steam Systems

There are seven school buildings with steam heat. The High School (it actually has two boilers but one is abandoned because it rusted out), a Sixth Grade School, the District Offices, an alternative High School and three Elementary Schools.

There are also two Elementary's and the Middle School that use hot water boilers. The other four buildings use one or another combination of gas and/or electric.

Most of the specifics in the latest postings relate specifically to the High School, although general ideas and principals are universal of course.

I will post some photos separately. I take pictures of as much as possible.

Thanks for your kind assistance.

Owen

High School System Photos, Boiler & HX #1

Photo #1: Front of Weil McLain 94 Series 3, #2094, I=B=R Gas Input 6856MBH, Gross I=B=R Output 5520MBH, Net I=B=R Rating Steam Sq.Ft. 17858- Steam MBH 4628. 163HP.

Note front riser height (36" from normal boiler water line to bottom of header), 10" header. LEFT: dead boiler, 1953 Pacific fire tube steel.

Photo #2: Power Flame power head burner (recently tuned).

Photo #3: Attempt at skimming Dec. 2010.

Photo #4: Front riser (of two), header, main off header up 4'8" (CL to CL) to near ceiling; all this should produce dry steam.

Photo #5: Left-Right: Steam riser, header, hot water supply line (I think), air separator, hot water return line, TPRV on hot water line (red), steam supply line to HX, 1/3 & 2/3 steam supply line valves.

Photo #6: Hot water line expansion tank.

Mark Eatherton

Correction....

You size the head of the pump for that zone with the highest pressure drop. Not necessarily the LONGEST loop, but THAT loop with the highest pressure drop, which may or may not be the longest loop. Gotta be careful and mindful of what you say on a public forum. Easily misunderstood, then misapplied with negative results.



As for the standard practice of adding 50% to the head calcs to compensate for fittings, it generally results in significant over sizing of pumps which can result in other mechanical problems. I'd prefer to do an actual fitting take off. Adding 50% is a lazy way out. I know, it is a standard practice, but that doesn't make it right.



On commercial buildings, unless the system is using 3 way bypass valves at the points of use, I'd prefer to set a variable speed pump or a pump controller that could make the pump a variable speed, based on head pressure. CLose off any bypasses or pressure differential devices.The load is not a constant. Why should the pump be operated as if the load were a constant?



Even if it were a 3 way bypass at the P.O.U., a program could be written to allow variable speed based on temperature differential, with a minimum required feet of head to overcome system resistances.



Just my $0.02 worth...



ME

furnacefigher15

He ask what an engineer would do

not what they should do.



Most engineers, even the ones that labor tediously finding the right size pump, add a safety factor, and many times a big one.



As far as frequency drives, I'm right with you. But I prefer running based on Delta p instead of delta t.

furnacefigher15

Owen

Where does the water feed pump tie in?



I don't see the equalizer line in the photo's.



I may have just had an epiphany!



You said the problem got worse when you changed the condensate receiver tank. I assume the pumps were replace as well, and with bigger pumps?



If the equalizer line is not large enough, and the condensate feed is tied into the equalizer line, but too high, then when the pump feeds water, it will shoot some of that water up the equalizer and into the header. This would have gotten worse when the receiver was changed with larger feed pumps.



Once the water is in the header, it will remove the heat from the steam causing more water, uneven heating of the building, and also prevent the boiler from making pressure.



In a pumped return application, the only function of the boilers equalizer is to allow any header condensate to drip back to the return, it not longer prevents the water from backing out into the return, b/c there's a check valve to keep the boiler feed / condensate return pump isolated from the boiler.



Please take photos of the boilers equalizer, and feed water tie in.





Also, the water level in the picture is way too high, especially since the supply tapping is on the side, instead of the top.



Also. all the pressure controls are piped in a way that condensate will stay in the control line.



The controls should be higher than the tapping (not lower), and there should be a control loop (looks like a pig tail) to keep the condensate out.

Owen

Epiphany

Ouch! Is an epiphany the same as when I realize I've been a damn fool and embarrassed myself? I do that all the time.



Receiver tank did not get new pumps when changed. I re-installed the originals.



Gosh, I sure hope you are onto something, and I guess I understand it.



Give me an hour; I'll run over there and snap a few pics of the stuff you've mentioned and post it here.

Man, I can't thank you enough!

Owen

Pumped Return and Controls Photos

Photo #1: Receiver tank & pumps, note SS check valves (new, very spendy); note level of fresh water fill valve/switch.

Photo #2: Pumped condensate return line, Hartford loop. (Note: fresh water fill is into the RECEIVER TANK, not into the return line; it was into the Hartford loop. I changed it when installing the new tank which was the whole idea behind the new tank; that was insisted upon by my water treatment specialist, water softeners also).

Photo #3: Second shot of #2. (Note: plug below ball valve is where the fresh water make-up used to go into the boiler; capped line was condensate return to the old dead boiler).

Photo #4: Pumped return leaves the receiver and goes way up to the ceiling about 13-14 feet from the floor:

Photo #5: then down & over to the Hartford loop.

Photo #6: Front of boiler; LWCO & MM #159 fill valve/switch LWCO. (Note pressure!)

furnacefigher15

I think I may be right

The point where the feed from the pump ties to the boiler is very high.



I would pipe it to the base of the boiler, such as that drain right there in photo 3.



I would try that, and see if that helps.



The system should heat just as well at 8 psi as it will at 3, since it's 2 pipe. The only difference is the fuel bill.



Also the equalizer (header drip) looks small. What size pipe is it?

furnacefigher15

One more thing

The other possible issue with the new, larger condensate receiver is that if it has a higher inlet then the old one did, and the condensate now goes up into the receiver, then there may be a water seal in the condensate drain line that feeds the receiver, preventing the air from escaping the system.



That vent to atmosphere on the receiver may be one of the only air vents on the return side of the system. Air can't push through a water seal.



And, if air can't get out of the heat emitters, steam can't get in very well.

Owen

Feed Hight

I'm trying to open this photo in Paintbrush so I can annotate it where I think you are referring. Coming soon!

Owen

Receiver Tank

The 280 gallon tank in the boiler room is only one of six receivers in various parts of the building. They pump from one to the next, ending at the big one.



Yes, the inlet on the new tank is about 18-20" higher than on the old (20 Gal.) one.



Photo #1: This is the old receiver and last of the return lines (end of the road).

Photo #2: This is the new return line right before shoving the new tank into place.

Photo #3: This is the drip, strainer and trap off the big 8" main as it drops down from the ceiling and heads into the main building (underground 40'); this line continues to the tank; the second line coming into this one is the pumped return from the main building; there are then three more lines that dump into this one, two from this side and one from the other direction (plus one 3/4" pumped line from HX #2 Trap and condensate tank that dumps directly into the big tank).



It's probably all screwed up, but I was one proud old tile-setter when I was finished putting it all together! It involved the piping (and there was absolutely no room for error on pitching all these lines to hit the tank inlet at the right level) as well as the electrical, feed water lines and the chemical injection pumps and quills. It even worked! Or so I thought.

Owen

Reply w/Pic "One More Thing"

Please see comments on photo.

furnacefigher15

As long, as

The only thing feeding the final receiver is pumped from other receivers, it's fine.



But I imagine there are traps in the tunnel, and in the mechanical room that drain to that receiver. And if they are tied in before the rise to the tank, then they won't vent air, so you may need to add vents to the outlet side of any effected traps (easy to do on the hoffman traps).





As far as the Hartford Loop, its not needed in that application because of the pumped feed water. The check valves on the discharge of the pumps do the same thing the Hartford loop does.



(I'll find a source for the Hartford loop issue, and quote it, once I find it.) Stay tuned.



The Hartford Loop is absolutely a must on gravity return, but not with pumped return.

Owen

Return Line

As shown in the photo there are several drip & trap lines into the main return line as well as a gravity return from a separate building (Welding & Woodshop) also the return from HX #1 after a big bucket trap.

furnacefigher15

I found it.

Page 67 from THE LOST ART OF STEAM HEATING.



"When a condensate or boiler feed pump returns condensate to the boiler, fitters often cut out the Hartford Loop. They do this so pumped condensate won't shoot up into the steam header. That's why those old timers who used the Hartford loop in their return piping oversized the equalizers on pumped return systems. They wanted to slow the condensate down so it went down instead of up when it hit the equalizer.



Nowadays, we usually pipe the pumped return to the bottom of the equalizer line. In a pumped return system, the equalizer acts only as a drip. It has nothing to 'equalize' because the steam side and condensate side are now independent of each other. Water can't back out of the boiler because there's a check valve between the boiler and the feed pump."



It's hard to see what all is going on it that photo. But it looks like a pumped return is tied to the same pipe as a gravity return.



Does the gravity return have a check valve to prevent back flow from the pumped return?



Also is the tie in to the receiver higher then the tie ins in the photo?



Yes, tie in the boiler feed to the bottom of the header drip/equalizer.

Owen

WOW!

OhMyGod! I think you've got it, several at once!



Hartford loop! I knew all that from Dan's books that I do have. That is, the lack of necessity of the thing on pumped returns from a receiver. But I just figured, well, it couldn't hurt. Obviously, it can.



Pumped return is tied into same line as gravity return, and no it does not, as of yet, have a check valve, but it will ASAP.



Tie ins to receiver higher than...?

Please elaborate.



I will be tying in the return line to lower on the equalizer ASAP also.

furnacefigher15

Tie ins

What I'm asking is.



Those return lines in the picture, do they flow down hill into the receiver, or do they have to flow uphill?



Any of the Non-pumped returns/drains/drips should flow down hill into the receiver, so they can drain completely during an off cylce.

Owen

Returns and The Inspector

All gravity returns drain downhill (SRDH), more or less, at least all those in these photos.

That's something I'm very proud of, that there was no room for fudging in piping all this stuff going in that new receiver tank. It had to be JUST SO, and I did it. Except for no check valve in the one line from Industrial Arts Building, it works.

In other school buildings there are LOTS of problems with pitch (grade, slope, whatever),

and there at the High School too, just not on this short section. I've corrected quite a bit but have a lot left to go.



One more thing, if I change out the pumped return and get rid of the Hartford loop, is that going to fly with the boiler inspector? He comes around once a year.

He works for the Hartford Inspection and Insurance Co. and so may have a particular fondness for that feature.