Problems with a big vacuum system in Chicago

DanHolohan · March 2010

(I'm posting this for a contractor who was having a difficult time posting. - D.H.)

We have a 26 story condo building on Lake Shore Drive. Extremely well maintained steam boilers and vacuum pump system. Stationary engineer on staff 24 hours a day. The engineer has been in the building for over 25 years. The problem started about three months ago. One tier of the system does not heat and the condensate returns from several tiers stay below 80 degrees for hours, never really heats up.



Some facts:



*The engineer has ran this system in a vacuum 25 years and before he even started there it ran lie this. 

*The boiler stays in a vacuum during the entire heating cycle.

*Steam down feed system.

*He runs the system with one boiler unless it is below 15 degrees outdoors.

*The boiler has an input of 8,600,000btu’s

*We have run two boilers each at 8,600,000 total of 17,200,000btu – outdoor temp. 49 degrees

*Incoming gas pressure is more then required.

*After running both boilers for 60 minutes we still have condensate return lines below 69 degrees in this one section.

*We have end-of-main traps in the basement at 155 degrees. They tie into the main return pipe and the temperature lowers to below 85 degrees.

*We have changed all ends of main traps, float & Thermostatic.

*Installed gauges on the tier up stream of the trap with the problem and the end of main stays in a vacuum of 5in wc / the return gauge reads maybe 6in wc vacuum. 

*Shut off the gate valve to isolate the steam main from the main condensate return pipe and the main stays at the same vacuum reading. 

*Vacuum pump keeps the system in a vacuum of 8in wc when boilers are off. Then the boilers start up and approx. 20 minutes later the vacuum may rise to 3>5in wc during heat run.

*Checked all valves and they are wide open.



My questions are:

*Why are my condensate lines so cool for a section of the building?

*Is it uncommon to have a steam system run in a vacuum during the entire heating cycle?

*Why can I run two boilers and still have what appears to be no steam movement?

*What tests can I further run to determine the cause?

*Am I overlooking some simple solutions?



I thank you for your time,



Bob Crokenower

Steamhead · March 2010

Something is keeping the steam

from getting into this "tier".

First thing I'd do is check the vacuum readings in the problem area against those in an area that's working well. If there is a restriction in the steam supply, the steam lines on that tier should be under more vacuum than the same lines on another tier that's working. You can take the vac readings in different places along the steam lines to find the restriction point. If there are no gauge ports, you can drill and tap 1/8" pipe thread holes and plug them when finished.

It's possible the main shutoff valve to the tier is broken. Checking the vacuum on either side of the valve would tell you.

If you keep striking out, get in touch with Dave "Boilerpro" Bunnell. He's out in Amboy but will come to Chicago if needed. Follow this link to Dave's ad on this site:

http://www.heatinghelp.com/professional/105/Boiler-Professionals-Inc

ttekushan_3 · March 2010

I'm voting for air leak

Hi Guys-- Long time!

An air leak at an expansion joint or somewhere in a unit would definitely cause a lousy pressure differential and it wouldn't even need to be a steam pressure diff. It could be an air diff! I would guess that the air leak is in the tier that doesn't heat and the tiers with cool returns are somewhere adjacent to the non-heating one. It wouldn't matter how many boilers you have running either.

Or not. But its worth a look. I suppose a clogged lift fitting could be at issue but it doesn't sound like you have any of those considering its a downfeed system.

What kind of system is it? Is there a manufacturer name associated with your vacuum system? Subatomospheric steam systems certainly could be designed to to maximum vacuum on start up, but it seems that they usually shut off the vac during full shut down. E.g., an Nash Jennings might have the vacuum pump operate off a float switch in a return reservoir. Or maybe the original vacuum pump was a vacuum boiler feed pump and has now been supplanted by a traditional boiler feed system with a vacuum pump on the way to the reservoir tank. Regardless of whether you have a liquid ring type pumping system (like Nash Jennings) or a venturi type (like Domestic by McDonnel & Miller) the pump usually ceases once the system shuts down.

Another thing to look for would be a giant steam modulating valve somewhere on the steam main in the boiler room. Those were sometimes used to control the level of vacuum in the system. In that case, the vac pump may have run based on condensate return load with the vacuum in the system being set by the amount that giant valve is open. Fully open- relatively low system vacuum levels; closed down- high system vacuum levels. This steam throttling valve would be set automatically based on outdoor temperature. Anyway, I'm guessing that the high vacuum at all times is due to something missing, broken or bypassed. Now, its probably just fine that it pulls a pretty deep vacuum on the system. Its more efficient that way if you can keep the building warm. You just may want to allow the pump to shut off after certain amount of time. Perhaps a steam temp sensor on the boiler would be adequate to shut it down if the system cools down long enough.

But the matter at hand-- air leak.

-Terry

Steamhead · March 2010

In that case

there would be less vacuum in the steam lines on that tier.

ttekushan_3 · March 2010

I think it does.

"Installed gauges on the tier up stream of the trap with the problem and the end of main stays in a vacuum of 5in wc / the return gauge reads maybe 6in wc vacuum. "

I'm reading this to mean that there is a deeper vacuum on the return (6" vac) than on the supply (5" vac) leaving a small pressure differential. Assuming the system is steaming during measurement and supplied with substantial vacuum pump capacity, I can visualize air at atmospheric pressure drawn through, and expanding into that tier's main -just enough to fully displace the steam with the steam taking the route of greatest pressure drop which will be towards other mains, being drawn by both powered vacuum and condensation vacuum.

I think the pressure in the system would have to rise up just within the pressure drop through the (theoretical) piping breach for the tier in question to begin heating. If we were to develop positive supply pressure, the location of this (admittedly mythical) leak would become obvious.

So I'm going to dig in my steamy heels and gleefully stick with "magic air leak" theory. Guaranteed or your money back! ;-)

-terry

edit- I'm also assuming that since this a downfeed system that one sizable main runs to the roof area and drops with each tier taken off the drop in succession as the main descends. This would mean that the basement has roughly as many end of mains as there are floors/tiers. I hope I was reading this right.

Steamhead · March 2010

Once we compare those readings

to those on other parts of the system that are working, we'll know what we're looking for. This is going to be interesting.

ttekushan_3 · March 2010

the contractors predicament here notwithstanding,

I really like this kind of question on The Wall. Gives us something to sink our teeth into. I'm really curious with this one, no matter what it is.

Not just steam heating, but Vacuum Steam Heating-- filled with Intrigue, Suspense, Money, Sex and Fame!

Of course, if its some stupid clogged strainer or clogged F&T, I'll scream.

Robert Crokenower · March 2010

problems with big vac system in chicago

Thanks for all the input. on Monday 22nd we will be conducting some tests, the leak theory has been one that we just kicked around over the weekend, we will pursue all the opinions I have heard, I need to find the problem and all your inputs give me more direction I'll keep you posted.

Problems with a big vacuum system in Chicago

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