Band-aid for steam + DHW zone?

Jim Franklin_2

Today as I was about to go stuff my gut with turkey, and be gone for some 12 hours, the house got really warm. That meant the DHW storage tank was calling for heat but not getting any and the boiler would run forever. 3rd time this has happened in a year. The plumber who piped the Superstor zone into my steam system using boiler water (not the tankless coil) for the zone said it was air-bound and I should bleed the zone. Since he provided no bleeder I can't do that. Besides, it's an open loop using boiler water, it shouldn't get air-bound. The "from boiler" piping (containing the circulator and tapped into the boiler mid-level) for the Superstor is very hot (even past the circ and into the tank) but the "to boiler" (returning to the bottom of the boiler) is stone cold. My theory is that the water is flashing to steam at the circulator suck side. Make sense? Any other causes?

Once I let the system cool so there's no steam pressure, the loop works fine. The water level was above the tapping so it isn't running dry unless the water level isn't level (tapping is on the opposite side from the steam risers).

Is there a cheap & easy fix until I can re-pipe it correctly in the spring? Maybe a controller that limits the system to 180 when the stat in the Superstor calls for heat?

thanks + happy Thanksgiving,
jim

Steamhead (in transit)

Repipe it

I think you've nailed the problem. There's not enough static head pressure at that mid-level takeoff to keep the water from flashing to steam. The circ should pump away from the bottom tapping, into the indirect and return at the mid-level one.

Also install an aquastat where it will be submerged in boiler water all the time, and wire it so that when only the indirect is calling the boiler will not exceed 180 degrees.

Lastly, pipe a small bypass line which will lower the temp of the water entering the circ so that when the boiler is steaming, the water entering the circ will not exceed 180 degrees.

Then watch how well it works.

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bluemoon

We always take the feed water from the lowest practical tapping & return higher...to avoid drawing steam into the loop....are you feeding high & returning low?

kevin coppinger_4

Your thoughts....

of drawing from the bottom are a nice idea, I did that once...then went back and changed it when the superstor HX plugged...Steam boiler bottoms are nasty places. I probably will not do another indirect off a steamer again... kpc

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