Help to settle a discusion

MikeC

I was having a discussion with our local union instructor this evening concerning steam pressures.I was lamenting about finding most systems set at 5# without regard to the total pressure drop of the piping.I mentioned that the Empire State building is heated with 5# of pressure.I know I had read it someplace here or in an article by Dan.The instructor was struck in disbelief and stated the steam would completely condense in the risers before reaching the top.Help me out guys,I need some facts.
Mike

Steamhead

If you follow his \"logic\" to its conclusion

higher-pressure steam would condense faster than lower-pressure steam, since the lower the pressure, the faster the steam moves.

Then refer him to all the Trane Vapor systems that have graced the Wall recently which distribute steam on an ounce or so- especially after venting upgrades.

Last but not least, acquaint him with the 2-pound standard introduced around 1900. This stated that any steam-heating system installed in a residence shall be able to heat the house to 70 degrees when the outside temperature was 0 degrees, with no more than 2 pounds of steam at the boiler. If the system did not meet the standard, the contractor didn't get paid.

If the Dead Men could do it, we can too.

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Tony Conner

As Long As...

...the line is properly insulated, you can push low pressure steam a long ways. And, as a compressible fluid, it doesn't matter whether it's up, down or sideways, the pressure drops will be the same. The central steam system I worked for had 10 PSIG sections that ran for 5 or 6 city blocks at a stretch.

Your instructor could be confusing heat loss with pressure drops. With long runs of low pressure steam, the lines have to be quite large, as compared to the same steam load fed by high pressure. What can be fed through a 2" 125 PSIG line may be the same as a 6" line at, say, 5 PSIG.

Remember that residential/small commercial steam sytems will typically be set up a little differently than most big systems. In large industrial or institutional systems, a 4 PSI drop in 500 feet of 125 PSIG main will be pretty common. You've still got 121 PSIG at the end of the line to do whatever it has to do. A 4 PSI drop in 500 feet of 5 PSIG main will be a problem. You've only got 1 PSIG left, and it likely won't do much, especially after a control valve. The line needs to be larger so there's more pressure at the end of the run. Most newer commercial/institutional buildings have hot water heating. The same loop is used for A/C in the summer. Many use steam to a heat exchanger to make hot water, then pump it through the building. The steam never goes further into the building than the convertor station.

There are practical limits as to how far you can push steam. After a while (couple of miles or so), the pressure drops and line losses start to get you, and you're further ahead to feed it to a heat exchanger and make hot water. You can pump hot water for miles and miles.