2-Pipe Down Feed Steam System

matt_63

What are typical system operating pressures and temperatures of a 2-pipe down feed steam system with a vacuum pump. The apartment building is 21 stories high and has 168 aparments. The total building EDR is approximately 14,000. The system operates currently with 5psig steam pressure and 25" vacuum. Most of the apartments are overheated.

nicholas bonham-carter

vacuum system

does this have main vents in the attic, and then feed down from there?
how old is this system-1910?
what sort of boiler[s] do you have?
i'll let others more experienced than i weigh in on this; but my guess is well below 16 oz.
if the machinery is original and ancient, we would love to see some pictures!-nbc

matt_63

vacuum system

There are no main vents at the top of the up feed risers. The system was installed in 1956. There are (4) 450 HP firetube boilers supplying 6 identical apartment buildings. It is a metro piping system using a vari-vac differential controller and control valve in each building. The riser goes to the top fllor and then feeds down to a radiator on each floor. There are 15 risers in each building.

Unknown

vari-vac

That was a nice system, in it's time. Outdoor reset for steam.

The vacuum in the SUPPLY MAIN varied with the weather, and the zones could be at different steam temperatures (vacuum) within the same building.

The returns would be in a deeper vacuum, giving the steam a reason to move, but the steam was squirted into the vacuum in the mains by King Valves on the outlet of the boilers. The VariVac monitored the weather, the zone pressures, the space temps, and drove the King Valves accordingly. Pretty neat.

The good old days..

What do you want to do with it?

Noel

matt_63

I would like to know typical operating steam pressure and vacuum. We are currently at 5psig steam pressure and 25" vacuum. Most of the apartments are overheated. Are we operating at typical pressures?

Noel

pressures

The supply mains were typically at around 7" of vacuum, more or less, depending on load.

Vacuum in the returns ran in the teens.

Room control was manually adjusted at the radiators.

The boiler pressure ahead of the king valves was a pound or two.

Noel

matt_63

Noel Vari-Vac

Thanks Noel,

I believe operating the boiler at too high a pressure (5psig) and the vacuum system at 25" vacuum may be a big part of the problem of uneven heating in the apartments.

Unknown

You haven't mentioned the traps

Are the return pipes in the building cool enough to hold your hand on?

Overheating will occur in spaces that have a hot radiator trap (from steam in the return) and the radiator is less hot in the center of it.

Vari-Vac systems could have been installed with the (new) system, but usually were added as an after thought to save fuel. Therefore, the piping is probably not sized especially for vacuum, and you can run any pressure you need to to make the system heat.

New, it probably ran at 2 psi and no vacuum in the returns.

Check this out

Noel

matt_63

The system only has traps at the bottom of each down-feed riser and a globe valve at the base of each up-feed(supply riser). The metro piping system did this to eliminate the need to enter each apartment for trap or valve maintenance. There are no traps,valves, or air vents at the radiators All traps are checked on a monthly basis.

Thanks for the vari-vac component pdf.