Gee....

[Deleted User]

Wallies, I came across something today that I have not seen in my 33 years of seeing steam and hydronic systems. It was in a home built in 1935. The home was a demonstration home built by G.E. It has a steam boiler in the basement, along with a large air handler and fan coil unit. There are a couple of one pipe steam convectors in the system, only one thermostat and basically a forced air distribution system. Having never seen one of these beauties, I have numerous questions.

1. What casuses the differential in pressure across the fan coil to cause steam to flow? I see nothing that looks like a condensate trap. There is something in the supply under insulation that is labled "donut" in the pictures. Could that be an orifice or is it a union?

As for fan control, it would appear that there is a pressure switch that activates the blower based on pressure at the fan coil. Thermostat called for heat while I was there, boiler fired, pressure came up to around 2 PSI, fan started, system ran for a while, boiler shut down, fan continued to run until boiler pressure was almost down to zero.

It also appears that there was some sort of steam vapor humidifier that was a part of the original system, since abandoned. See attached photographs.

I forgot to look, but I think the boiler is an early American Standard or Crane atmospherically vented appliance.

You east coasters ever seen anything like this before?

TIA for your responses.

ME

Steamhead (in transit)

The coil

would behave like any radiator, in that once the air was out the steam would condense and pull in more steam. The vent on the coil outlet got rid of the air.

Interesting that there wasn't a GE boiler in that house!

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[Deleted User]

Soo...

No pressure differential device needed? Just suck the heat out of it and it condenses on its own eh...

Did GE make a natural gas atmospheric boielr Frank? This one did have adjsutable pet cocks on the inshot burners to adjust the gas. I should have looked closer at the boiler, but they were in a hurry to get home for the trick or treaters.

I've alwyas been under the inpression that if the emmiter (FCU in this case) had two pipes connected to it that it needed something in the way of a trap or orifce to differentiate between the supply and condensate return. Am I wrong?

Thanks for the info Frank.

ME

Unknown

I saw................

a setup simular to this "many-moons-ago", it was in a movie theater, it too had a large coil- one pipe, I can`t remember the boiler particulars, but there were also convectors off-it in the WR. and managers office. Brings back memories for me as this was one of my first exp. with steam!

Steamhead (in transit)

It would need

something to keep the steam from getting into the dry return, if one is used. That's where the trap (or water seal, etc) comes in. The differential between a steam main and a dry return is maintained by the trap (or water seal, etc) stopping the steam.

On this setup, it looks like the coil drips straight into a wet return. Since this return is filled with water, steam cannot enter it, therefore no trap or other device is needed. The only thing you need is a vent to get the air out of the coil.

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Joe V

I used to

...work for a thermal processing equipment manufacturer that occasionally used steam coils as a heat source. We always used a modulating steam valve, F&T traps and occasionally a condensate pump to control temperature. The inlet side of the coils always had vacuum breakers to keep the coils from collapsing when the equipment shut down and the coils cooled. A different application than yours but the same design theory may be used.

Our coils were mfrd by McQuay; their site may provide that one piece of info you need to make sense of what you saw.

[Deleted User]

Thanks Frank...

I will try and generate a drawing of what the piping arrangement was.

Thanks for the learnin'.

ME