Not a good day for coils

jacobsond

On my greasing run today and I came across 2 steam coils leaking. One had a leak where the tube meets the cast iron header. They tried to braze with no luck. Then had a guy come out and used Belzona on the leak. All seemed good until today 3 months later. Leaking in the same area. Not sure if same place or just another tube. I will have to pull the coil out as far as I can and check when the temp gets above 0. It may be able to keep up with the preheat coil then. We cannot easily replace the coil. There are stairs in the way that would have to be removed 1st. The coil is aprox 7ft long and 4ft tall. I would guess 40+ yrs old. Anyone have any luck with a product we could use in this area? Running 8lbs steam. The AHU next to it has the heat coil also leaking. Have not dug into that yet. Dont want to shut that down until better outdoor temps. Oh happy day. Cant wait until spring so I can catch up.

EBEBRATT-Ed

Brazing it is the only thing I would trust. If the header is CI and the tubes are copper I would use bronze brazing flux coated rod

mikeg2015

Might just have to replace the single coil with two coils. Also evaluate if it needs a could that big.

Some commercial buildings required 30% outside air by design because people were allowed to smoke indoors back then.

Unless this is industrial.

neilc

did you ever figure out why you're running 8#s ?

jacobsond

I have not figured out why we run 8. The main supervisor is now wondering why we pump out 80 on the high side. Thinking of lowering it. Other colleges in the state are running lower pressures he has learned. I may be able to convince him to lower the low side also. He is a smart guy but not a steam guy. Willing to learn tho just like me. The big obstacle will be the head of the heating plant. He is only 50 but has been in the plant 25+yrs. Was taught by the previous guy. He doesn't like change and I would guess not sure why we need 8 or even 80. As far as the coils go we have taken coils to welding shops that fail on the pipe to header connection so not sure what to do at this point. Hopefully the other coil leaking is not at the header,but its a royal pain to gain access. The one with the header problem can easily be pulled out 3 ft before you hit the stairs then we are in trouble. I think they are only leaking a couple gal of condensate a day. Not terrible,but still need repair. We need 20 degree nights to be able to run on one coil so may have to wait. One supplies the pool the other the locker room. We cant let them get cool. There is a Spence regulator valve in this mech room. Maybe I could sweet talk someone to do an experiment on a lower pressure so we don't loose so much. Would that be an option?

clammy

Usually on steam and ahu the longest lived coils for steam application is a non freeze tube in tube specify for 2 pipe any other type of coil will fail on steam or not heat evenly and correctly . If there s a control valve and trap I de make sure that there’s a vacuum breaker of rated for steam . I would image there’s are for reheat so I would suggest that there be a freeze stat mounted on the coil . Just another note if there is a control valve weather it pneumatic or electronic it should be a powered closed valve so if there is a control or power or air issue the valve is open preventing coil and space freezing . I know this is old school and I would image not all can remenber back that far but I see guys installing water and steam with out a clue first freezing day or power outage and there either repairing or replacing coils . N F tube in tube coils are not cheap last ones we did we had to order and it was a bit before they can and there where not cheap but the old ones where original install from like the mid to late 60 s not bad . If you have the units model and coil number contact the manafacture they could have one sitting in a warehouse . I got lucky once and got a new tube in tube old stock for a carrier ah who would believe sitting in a warehouse in a crate for like 45 years or something spanking new minus 45 years of Kentucky dust but it was like 1/3 the price of having one made and the coils issue was leaks but at like 40 or 50 years old they got there moneys worth . Most that I have replaced did there time and it seems that after the first couple of repairs they really start to fail nothing last forever Peace and good luck clammy

jacobsond

Most things here are old school. Pneumatic controls everywhere. I actually have less trouble with the pneumatic than the electronic. Valves fail open with power or air fail.The confusing thing to me is a freeze stat trip and the valve closes. When the coils leak on the tubes sometimes brazing is tough because the tubes are so thin now. Pinholes all over. We need to start replacing but of course we are on a very tight budget. Im hoping for a magic epoxy to put a bandage on these tube to header leaks even tho I realize it is not the best way to repair. The Belzona guy said his stuff could handle the heat. Until I pull the coil and inspect I wont know for sure but I think it is a fail.

clammy

I de get a handle on the freeze stat it’s most likely wired wrong or wrong freez stat being the valve is closing need a normal closed . peace and good luck clammy

pecmsg

Freeze Stats

Outside air dampers close
Steam valve opens Pre and Reheat
Fan STOPS
Chilled water valve (IF live) opens and pumps come on

This is in general conditions. Every building has its own sequence for freeze protection.

A general book is the Honeywell Gray Manual of commercial building controls.

dopey27177

Had a thought.

Can you bring the new coil in through the plenum. That would only require the removal of the damper and frame or maybe bring the coil in thru a window. I know that this sounds freaky but I had some jobs in N.Y.C. where we had to get a crane and bust out the exterior wall to get a coil into the building.

I would keep doing the belzona repair until the warm weather comes. Meanwhile get a brain trust going to try and figure out how to do the job.

Here is another idea, have a coil built on site. Call the coil manufacture they may be able to accommodate you. Hopefully the coil is not serpentine.

Here is another idea pinch off the coil and braze the ends, braze a plate over the manifold and be done with the one tube.

Some times it is any port in a storm.

Jake

PS. Spence valves are terrific on coils, You can even get pilots that will control the steam inlet pressure and air temp leaving the fan coil coil unit.


Jake

jacobsond

Thanks All good ideas. Doing the Belzona today. We are going to look better on how to get this thing out. Just so you understand where its leaking. There are steel tubes I believe pressed into the cast iron header its leaking at that joint. The copper tube is brazed on about 2 inches out. No on here can seem to get any brazing to stick to the cast. Cutting the tube and brazing a plate seems beyond our skills. Espically with the coil pulled out only 3 ft. Everything rusty as heck. I used a portable sandblaster today to clean the area after I pulled off the failed belzona. Then file and wire brush. I used the Belzona 1321 that was recommended to us. This repair was done by the local belzona guy the 1st time. This time I wraped the area with their cloth and will put a second coat on within 2 hrs. I hope I can get away with not putting the coil in service until Wed or Thursday. We will see if the 2nd coil in the unit can maintain temps in the pool area. Above freezing outside today and tomorrow. Hope for the best.