Steam Coil Questions

barbarossa_2

Re your question: I was also given a calculation to test the output of the coil (CFM * 1.08)deltaT
That will give you the BTU's/H that is being transfered to the air stream.

Michael Wilson

Steam Coil Sizing and Piping- LONG POST

Hey guys!

I was out on an estimate today.. Customer complains of not enough heat... I checked out the boiler and its waaaay oversized for the building. I think there is something wrong with wither the sizing of the steam coil or the piping to it.






Sorry for the book i'm writing... ;-)



Picture this if you will... The 810,000 Btu boiler (running at minimum pressuretrol settings) has 4" Risers, Header, and Steam main. The main comes out of the header and runs 15' straight up to the ceiling. Then elbows left through a wall into where the air handler is.




There is approximately 15' of 4" main from the wall to where it hits a gate valve. Out of the valve is another 2' of 4". Here it reduces to 3" into a motorized zone valve (permanently opened). Out of the Zone valve is 2' of 3" pipe that then reduces down to 2" for another 2', hits a 2 x 1 1/4" elbow and the 1 1/4" pipe runs 5' into the top of the newly installed (not by me) copper coil. (The coil is already leaking, but that's for another day)



The 1 1/4" return line runs out of the bottom of the coil over to a f&t trap. 1 1/4" pipe runs out of the trap to the side wall (where there is a main vent) and connects to the wet return approximately 17' below the airhandler near the floor.


Misc. Info:



There are no markings on the coil or identifying model numbers.


It is approximately a 50" x20" rectangle.


The coil is connected to a 7.5 ton air handler.







Ok, onto my questions:







How can I tell if this coil is the right one for steam?



Is it sized right? I'm thinking the piping to the coil is a tad small, but the coil only has 1 1/4 taps.


I figured I'm going to need around 350,000BTUs to heat this building.



Also...If the condensate is dropping straight down into a wet return, the f&t trap isn't really necessary right?



Thanks for your time and patience!





Mike

ttekushan_3

good details

Are all those reductions in a horizontal plane without eccentric reducers or some other means of keeping condensate from pooling in the bottom of each pipe?

Does air ever exit the main vent? Is there a check valve in the return line anywhere?

Sorry about the edits. Ya get distracted and can miss a whole paragraph!

Michael Wilson

Horizontal plane

Hey Terry,
Thanks for reading my book!! lol




Yes, all are on a hoizontal plane using regular reducing couplings, no way to keep condensate from pooling in these spots.

I didn't hear the main vent let out any air at all, but i'm thinking this is because it is always pressurized with steam.


The boiler maintains steam pressure through out the season. The thermostat just operates the air handler.




And being grossly oversised, it never gets to 0psi, even with the airhandler running! this is one factor that makes me think the steam coil is undersized/not the right one..


When it calls for steam(air handler not running), the boiler runs for a total of 30-40 seconds, goes from .5psi to 1.5 psi



I did not see any check valves in the system at all... just two f&t traps... one before the abandoned zone valve and one after the air handler; sized and piped by the "well it would look silly" method...



mike

ttekushan_3

oy.

If the air vent is always closed with steam, I presume the return line is shared with something else? The F&T can't drain into a steam filled line. If there's pressure there on the return, the entire coil could be air bound between to steam fronts, one from the supply and one from the return.

If the return is for the coil only, the air vent shouldn't be closed with steam unless the F&T is blowing by.

Are you absolutely sure that the people who installed the new coil fully opened the gate valve that precedes the motorized valve?

You mention that the coil leaks already. Why was the old coil replaced, did it mysteriously develop a leak too?

I'm thinking that the coil could be caused to leak for a couple of reasons. One is that it handles fresh make up air which could have frozen it. Another is that its been water hammered to death from sudden steam valve opening carrying the water from those reducers into the coil.

Also if there are any areas where the condensate must "lift" any distance at all, the boiler pressure may not be high enough. Once fan coil unit heaters get involved, some piping layout require higher boiler pressure.

I'd shut off the boiler and loosen the union that connects the return of the coil to the F&T to see if a rush of water drains out. If it does, then the F&T could be clogged. IF there's no strainer, this is a real possibility. If there is a strainer, clean it out.

If practical, fire up the boiler with the line removed, just long enough to see if steam makes it into the coil as evidenced by a good flow of condensate.

BTW, where's the coil leaking?

As for its appropriateness for steam, it should be fine if the tubes appear to be able to drain towards the bottom collector. Steel heat exchangers are more durable for steam, but I've seen plenty of copper with no long term problems.

Look at modine, beacon morris, etc heating coils to get an idea of their coil dimensions and blower CFM. You'll need to make inferences. With the blower on, a vacuum is created in the coil. If the coil cools over a portion of its surface area, there's a steam supply problem, or air is being drawn back into the coil via the return lines. This is why there's supposed to be a check valve there, among other reasons.

Michael Wilson

Thanks!

Thanks Terry,

I'm going to check things out more throughly on monday and get back to you.


The f&t after the coil, wouldn't that act as a check valve for the return if it is working properly?



Or do I still need one? Between the coil and the f&t maybe?




Thanks again,



Mike

ttekushan_3

F&T

won't act as a check.

You are correct about the placement. The check goes between the coil and the trap to prevent any non-condensables to back up into the coil and displace incoming steam. BTW, if this is actually whats happening, it can at times be a violent process which can damage the coil.

You might want to take a picture or two. I have a mental image, but I could be all wrong. Its just like hearing someone's voice on the radio and you develop an idea of what they look like then you see them and whoa! was I off!

bob young

[vacuum breaker ]

possibly require vacuum relief valve [vacuum breaker ] maybe eliminate steam traps . & use conventional vents.the trapped concentric reducers sound like trouble .

an old wrench puller

Pictures would be good.

http://www.marlocoil.com/pdf/steamcoil_o&m.pdf

This gives some typical coil lay outs.

A vacuum breaker is a must. An end of main drip before the coil is a must. Does the F&T have any "Head" above it? Does the return come out of the very bottom of the coil? Does the coil pitch to the return? Are you sure the control valve is full open?

Get your self an old Hoffman engineering manual or a Sarco application manual.

What controls this set up?

Does it have a freeze stat?

Try to get some pictures, I'd like to see this...sounds a whole lot like a setup I seen not too long ago.

an old wrench puller

More diagrams

http://absolutaire.com/docs/component_docs/steaminstall.pdf

http://www.mcquay.com/mcquaybiz/literature/lit_aa_coils/IMOM/IM_901_Steam_Coil.pdf

http://www.uky.edu/EVPFA/Facilities/CPMD/standards/div15/15520D05.htm

Michael Wilson

Pictures on monday

I'll take plenty of pictures Monday and test all the valves before the coil.

At initial install(not by my company), the coil was taken out of any sort of box it may have come in and custom installed into the ductwork... it looks level to me... no slope to the drain.
There is no "head" above the f&t. It is on the same level as the return outlet... the piping to it is pitched slightly, maybe 1/4" or 1/2" to the foot MAX.




Freezing is not an issue be cause 100% of the return air comes from the conditioned space. No make air up what so ever.



As far as controlling this setup, the Thermostat just operates the air handler. The steam coil is pressurized 24/7 during heating season. The only thing controlling the boiler is the pressuretrol.




I was also given a calculation to test the output of the coil
(CFM * 1.08)deltaT



Is this the right formula?



Thanks so much!


Mike

tim smith

I am betting on too low of steam pressure, don't ask me how

I know but ran into similar issue lately where the steam unit heaters would take all available steam before we could get steam out to an extended office radiator circuit. Came into this one cold and took a little while to figure why we could not get flow to this office circuit.

Michael Wilson

Pictures and video

I know they say a picture is worth a thousand words... what about video? ;-)


Snapfish Picture album: http://tinyurl.com/cvq2f2
Youtube Video:




And no, that's not my helper banging on the ductwork... that's the lovely sound of water hammer.



The daycare director says it scares the kids!


If only it scared the installing contractor more! LOL!



I did my calculation... (~2600CFM*1.08)40= 112,320 BTU







CORRECTIONS TO MY FIRST POST:
Pitch is wrong, the coil is not level.



There is a eccentric reducer on the 4" Line, it reduces to 2 1/2" not 3" as previously stated. The 21/2" is then reduced with an elbow and a bushing down to 11/4".



All valves are confirmed open.



Picture # 003 corrects my statement about proper pitch. Check out the feed coming into the top of the coil.

Michael Wilson

Pictures and video

I know they say a picture is worth a thousand words... what about video? ;-)


Flickr Photo Album: http://flickr.com/photos/34793109@N06/
Youtube Video: http://www.youtube.com/watch?v=dEI0aIrG1t8



And no, that's not my helper banging on the ductwork... that's the lovely sound of water hammer.



The daycare director says it scares the kids!


If only it scared the installing contractor more! LOL!



I did my calculation... (~2600CFM*1.08)40= 112,320 BTU
Do you think if we get rid of the vacuum and get the condensate out, the output will increase?






CORRECTIONS TO MY FIRST POST:
Pitch is wrong, the coil is not level.



There is a eccentric reducer on the 4" Line, it reduces to 2 1/2" not 3" as previously stated. The 21/2" is then reduced with an elbow and a bushing down to 11/4".



All valves are confirmed open.



Picture # 003 corrects my statement about proper pitch. Check out the feed coming into the top of the coil.

Steamhead (in transit)

AH piping

What a list of errors. Pitch is bad, plus long horizontal runs, plus no insulation on them. Do you know why they disabled the motorized valve? What is the method for controlling the steam flow? You would think it would be closer to the coil and bucket trapped just prior to the valve. I liked the video by the way.

Michael Wilson

Steam flow/valve/traps

Glad you liked the video! Sure beats 50 pictures!!



The steam isn't really controlled by anything but the pressuretrol. The pipes are energized 24/7, whether the system is calling for heat or not, thus causing the back area to over heat.



I have no idea why the previous contractor disabled the motorized valve, and some how i doubt he'd answer my questions if I call him. :-O



I'm sill a bit fuzzy on why I need that trap if the coil condensate runs to a wet return with nothing else connected to it.



The way i see it now, that line between the coil and the trap always holds water, most likely because of the vacuum in the coil. After I install a vacuum breaker will the trap be necessary?



Thanks again guys!



Mike

ttekushan_3

vacuum breaker

The vacuum breaker is only there to prevent the crushing of the coil in the presence of a return check valve or the siphoning of water back into the coil in the absence of a check valve should the motorized valve close.

During operation, that vacuum breaker does nothing. As you stand right now with no check valve (an F&T is NOT a check valve, and does not function as one) and no supply valve closure, those are your vacuum breaker. Install one in the proper place to avoid destructive accidental closure of any supply valves.

The vacuum I'm speaking of regarding poor coil performance is one that may form within the mid area of the coil due to condensation of steam. This is called steam stall. Rather than drawing more steam into the coil, the void can be filled from the return side, which is one reason you NEED a check valve. Then adjust supply pressure to allow full heating of the coil and condensate drainage when the blower is operating.

Also check for trap blockage. I know you really want to remove that trap, but that is not going to help you with this problem at all.

Those motorized valves can fall closed over time. Someone might have turned the valve operator by hand and destroyed the contacts. Mis-wiring of the actuator can also destroy the motor if its not spring return. Regardless, I'm sure someone felt the cost of replacement parts excessive.

The only reason I could see that the boiler is left on pressure all the time is because the water hammer must be horrifying on start up. The near boiler piping certain looks as though there is no means of drying the steam.

So.

1) Level and pitch piping.
2) Insulate all supply piping
3) Install return check valve and supply side vacuum breaker
4) Check F&T and strainers for debris, cleaning as necessary.
5) Adjust boiler pressure for complete coil heating when blower is running.

and optimally:
6) operate boiler from thermostat
7) Install aquastat on coil return line (preferably using a thermal well and probe) to operate the blower
8) install a proper drip station in the supply where that dinky little thing is on the Tee. The drip should have a full line size pipe coming down with a Tee going to the trap and a capped mud leg extension from the trap take-off.

Did I mention the check valve, vacuum breaker (and thanks for those who pointed that out, it slipped my mind in my original post), leveling and insulating the pipes and boiler pressure adjustment as necessary?

-Terry

Valblughmug

Thanks Terry and everyone!

I went and looked at this again today, I bet they think I'm stalking their heating system!



The reason the feed line to the main is back pitched is because the coil/air handler is too high! They missed the air handler with proper pitch.



I'm going to have to repipe it, starting with removing that 2 1/2 elbow pointing down and bringing the pipe over. Hopefully i'll make the coil with 45's or a 45/st45 combo.




Everything is making sense as far as the traps go. Vacuum breaker on the supply side, check valve on the return side.



One last question, do you think i should remove that motorized valve and just install pipe where it was?




Thanks for everything guys! I'll keep you posted if I get the repair job!




Mike

an old wrench puller

My thoughts

Based on what you’ve said and I can see here, this is my take on this situation.

The Goal here is to provide the driest steam possible to the coil.


Let’s look at the components.

The boiler. In the pictures it does not appear to have a proper header. I would repipe it per the manufactures recommendations.

The Control valve. Why was it disconnected? Does it work? How did it work? On / off or modulating. What caused it to work?

On this system I would recommend a modulating control valve that is operated by a wall stat or a sensor in the return air duct. The end switch, in the valve, would be connected to the boiler, to turn it off.

If you do not want the valve in the system, remove it and the drip trap associated with it.

The coil. Is it a steam coil? If so, Pull it, braze up the leaks and put it back. Make sure the tubes in the coil pitch to the drain. Most steam coils have this built in so the frame can set level. So check closely, to be sure they are pitched correctly.

The Piping. From the time the riser turns horizontal, make sure the pitch goes toward the coil, all the way. If you leave in the valve, I would increase the drip leg to the trap in front of it to 2”. Come off of that with ¾” to an F&T, properly installed of course.

Out of the control valve I would take 2 1/2” all the way to the coil, a full size drop with the 1 ¼” coming off it to the coil with a swing joint. At least a foot below the coil take off, will be the take off for the end of main drip trap. A full size dirt leg with cap under it. Properly pipe the end of main drip trap. A vacuum breaker and air vent on the 2 ½” just before the 90 that looks down. I like a ½” swing check for a vacuum breaker. The air vent could also be on the discharge of the coil, before the trap, but put it on a stand pipe so its above the inlet to the coil.

Come straight out of the coil, full size, turn down, take off for the coil F&T at least a foot below the coil, then a full size dirt leg and cap.

I pipe F&T’s in this order: Gate valve, strainer, union, trap, union, check valve, gate valve. Make sure you have lots of pitch all the way back. Increase the pipe size as you tie the returns together.

Looks like this will be a nice little, even fun job to do. Good luck.