New return line to boiler feed tank, problems?

Pumpguy

The attached picture shows a connection from an existing, looks like 3", return line on a 2 pipe steam heating system.

The new horizontal return line connecting to the boiler feed tank is 1.25" pipe size.

This equipment replaced the circa 1927 vacuum condensate pump that was original to the building.

These boiler feed pumps feed a pair of 30 HP boilers which replaced the original 60 HP boiler. These were chosen only because of access. Existing doorway access wouldn't allow passage of new 60 HP boiler so a pair of 30 HP boilers were chosen instead. Usual MO is to operate both new boilers together.

If you saw this piping arrangement, and knew nothing else about how the system now operates, how would you think this new arrangement would affect the overall operation of the system?

1B1AEEB9.jpg

Pumpguy

More info:

This is in a commercial / manufacturing 3 story brick building with lots of large windows. With both boilers firing, it takes about 2 hours to get the first floor to 68*F. and the 2nd and 3rd floors don't get above 50*F.

In addition, they are experiencing what I call a starve-then-flood condition with the condensate. Boilers run until boiler feed tank has to take on make up water. Then when boilers shut down, all the condensate comes back, flooding the boiler feed tank.

The boiler feed tank has a 100 gallon capacity which should give at least 20 minutes of steaming time before needing to take on make up water.

So far, installing contractor's solution to this problem is to add vacuum breakers to the system. Not sure if these would be on the steam side or the return side. I'm a little confused if this has already been done, or if still in the recommended stage.

I know what I would recommend in this situation, but I'm curious what you all have to say or recommend?

EBEBRATT-Ed

I guess they will have backed up condensate in the system. I don't understand why the return tapping's in the tank are so small but the installer decided that the pipe need be no larger than the tappings.

The 1 1/4 strainer is probably already plugged.

delcrossv

Umm. Weld 3" tapping to the tank and run condensate line full size?

Do I win something?

Pumpguy

Thanks for your replies.

I agree about the 1 1/4" pipe size. The OEM inlet tapping to the new BF tank is 1 1/4", so it appears thats what the installing contractor used. And of course 1 1/4" pipe is cheaper and easier to work with than 3".

I'm thinking this BF unit was designed to be used with a condensate transfer pump, in which case the 1 1/4" pipe size would be just fine.

My real concern is air venting this system. With such a reduction in return line size, there's no room for any air flow.

Combine that with the proposed, or maybe now even addition of vacuum breakers, the venting is now worse than before. We're adding more air when we should be concerned about removing air.

Add to this the fact that from day one, this was a vacuum return system where the air was mechanically removed rather than relying on steam pressure to push the air out.

Am I on the right track here, or could there be other problems with this system to cause such poor heating performance?

Intplm.

@Pumpguy have you been able to get any information as to how the system was performing before this work was done? Was it replaced due to failure/leaking issues? Was it performing similarly to how it is now after said work? Im just trying to take a step back and look at this a bit differently. And yes, I believe you are on the right track.

Pumpguy

The only reason the boilers and vacuum condensate pump were removed was because they were old and corroded. Boiler had leaking tubes, and vacuum pump's receiving tank was old riveted steel type, original to the building.

New boilers, boiler feed pump set, and removal of old vacuum system were done at recommendation of installing contractor.

I have no reports of any heating problems prior to this new equipment being installed.

EBEBRATT-Ed

If the piping in the building was sized for a vacuum system it could be way undersized to work as a non vacuum system.

That being said a 3" return for 60 HP seems quite large

retiredguy

Before I retired I saw a few of these screw ups and the end result was not a pretty sight. With the original vacuum unit removed there is usually a lot of restriction in the piping since the system was designed to be operated with a vacuum to assist with air removal, steam delivery, and condensate return. My advice would be to get with the building owner and tell him what he needs to do and I know you know what that is. If he doesn't heed your advice run away from this job as fast as you can. If I had been called to this job there would have already been a fight since I would have called the contractor an IDIOT for installing such a system. Increasing the 1.25" line to a larger size would probably be a waste of time and forget the vacuum breakers. One last thing, I will bet that the 60HP boiler was actually much bigger than that. I hope that this installation is not in OHIO since the codes were very different there. I have seen 60 hp boilers fired at more than 100 hp and older fire tube boilers were very forgiving.

Pumpguy

Thanks again.

My contact, the maintenance guy wants a vacuum pump. Building super is treading lightly with contractor.

This is all still in process. In the meantime, the building's cold.

We'll see what happens.

clammy

If the system originally had a vacuum return then as i see it ,it will never distribute steam in any timely manner as is obvious and w no steam reaching the 2 and 3 rd floors . As you stated and i would agree the addition of vacuum breaker will make it even worse . I can only imagine how much fuel they use and to get crappy results . I had looked at a building that after say 25 years finally had a vacuum return pump and boiler feed pump put back in ,like your job before hand it took over a hour or so to establish and during the cold ran 24 /7 after the install steam at the 16 th floor from a warm boiler in about 15 minutes and the boiler no longer ran 24/7 in the winter .The fuel savings as i was told where insane . In the 20 to 25 years they operated without the pump they spent easily over a million if not more all to save the expense of installing the correct equipment at the time for the job to match how the system was designed to operate . failure to do so just result in tail chasing until common sense and deductive reason are used . It used to work originally Duh most of the time its a battle convincing them but if you can track fuel usage without the vacuum return it will become apparent . Of course all other things will appear that have been neglected traps and vacuum leaks and all the jazz .

On another note as much of a hassle as it is in a huge building is there any idea of the connected edr so as to take out of the equation the boiler being way undersized for the job at hand ?

Peace and good luck clammy

Pumpguy

Thanks @clammy, I was told the radiation was surveyed as part of the sizing of the new twin boiler installation.

I was not told what the measured EDR was, and I expect this number was not presented to the user.

If I continue to be involved in this job, I will pursue this issue.

I was told by a colleague who had some idea of this building's size that in his opinion, 60 boiler horsepower wasn't enough.

Hopefully more to follow ………..

Pumpguy

Customer is still dealing with this problem. I've been told one of the things the installing contractor has done is to put cast iron check valves on the steam outlets of each of these boilers.

Would anyone care to comment on how these check valves would affect the performance of this steam heating system?

EBEBRATT-Ed

Probably not good. The flapper on the CI checks are pretty heavy. I can imagine the boiler building pressure and "burping" the steam out into the system.

Never seen check valves on steam unless it was a high pressure steam system. On those if you have multiple boilers you have to have a check valve and a gate valve on each boiler outlet or a combination non-return and stop valve.

The reason is with a HP system (hospital etc) they want to be able to work on an idle boiler and keep the system running.

I have never see a check valve on a low pressure system on the supply.

retiredguy

Those check valves used on high pressure boilers were called "non return valves", and were a common item. As ED said, it was very unusual to see them on low pressure steam boilers.