Hot water loop off of steam boiler

Jonny Boston

Does anyone have any experience running a hot water loop using the condensate from a steam boiler, with a bronze pump and ball valve bypass?

Ken_8

Yes! And it stinks as a way to add a HWBB zone!

The junk (scale, rust, "mud") test the seal constantly. Regardless of how "clean" the water, the junk blows the seal in all pumps in between one season and three - depending on so many variables as to be a major conundrum.

Dan has a few pics available that describe how to do it - but that begs the question of whether it ever should be done!

We find an abandoned tankless coil or perhaps side-arm HX to be the only way to assure some semblence of longevity and minimal trouble to be the ultimate solution. But, if it has to be off the condensate piping, do it right. Just remember not to promise more than a year before you toast the circulator.

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Unknown

I beg to add to this

I ran condensate loops with indirect water heaters at the college to make hot water for 800 college kids. I never ate a pump seal in the 6 years I was there.

I think the pressure at the suction port has more to do with pump seals disolving than the water quality does. If the pump isn't mounted low to the floor, with the suction port as close to the boiler as the bypass tee allows, the piping adds head to an already-close-to-zero inlet pressure.

If the whole run is short (and almost headless) and the water is going so fast that the return water temp is very close to the supply temp, you might be almost flashing to steam at the lowest pressure point in the system, the water lubed pump seal.

If you're sucking vapor, the seal isn't wet. It won't last long. If you find a leaking seal, and it doesn't leak when the boiler is hot and the pump is running, you have a hot vacuum on your pump seal, which allows it to run dry.

Cure it by adjusting the boiler bypass and boiler return valves. Make steam and shut the return valve into the boiler, running full bypass boiler water through the pump and indirect coils. Open the boiler return to get the supply temp to the indirect coils up to about 190 degrees.

Now check your return temperature. you are wanting about a 15-20 degree drop in temp through the water heater. If it's much less than that, the water is flying through the coils. This isn't a problem on hot water boilers with 12 psi on them, but it might be a problem on a steamer with no pressure on it.

To balance the heating needs of the indirect with the pressure needs of the pump, throttle the full sized bypass a little, to get the 20 degree delta T, and readjust the boiler return valve to keep the supply temperature cool enough that the pump seal doesn't flash.

I can't say enough about pump sizing for the proper gpm and head. The math is important.

Having said that, I wonder what's different about your city water and my city water in steam systems with condensate loops, Ken? Something is going on, for us to be on opposite sides of this one. I wonder what I'm not seeing.....

http://trainingroom.slantfin.com/articles/nm0304-1.html


Noel, on vacation and going bass fishing this morning.

Kal Row

dan recomends

running the boiler up to the max the reg pressuretroll setting, and set the supply bypass for 180, then take the handle off so that no one can mess with it

190 may still be a little to close to the flash point, if the NPSH drops for some reason - like boiler surging - happens even in the best of homes ;-)

Ken_8

I suggest the devil is in the details...

I'm talking about a small ~300 SF EDR boiler with no treatment, a 007 for a "pump," and rare (if ever) water chemistry or TDS testing.

Your talking about a constantly attended boiler, of much larger scale, with a demand and a vertical dimension from NOWL to suction inlet of a pump on the order of feet!

I'm referring to a "johnny homeowner" system where the circ. pump may only be inches below the NOWL - and the relationship of "crud" naturally occuring in the water is at much higher concentrations than a well cared for "commercial" steam boiler.

That's just for openers. Then we get into the off cycle of a zone in summer when the pump would just "sit there" - and you're referring to D/H/W required year round..

I think we're both on the same page. I just got there from the front door and you arrived via the back.

How's that for a mixed metaphor?

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Kal Row

007 on a condensate loop

is a "non-starter" pun intended!!!

ernie_3

off of condensate?

Why not run the loop off of the boiler? A plate type heat exchanger could be used. Circulate a loop to the exchanger w' a wye and strainer for annual maintenance. The other side of the plate is you baseboard loop, pump chk vlv, gauge
purge tee, prv, relief... Size the plate for your load.
Have had good luck w' these.

robert griggs

Does any one have any experience

with running a loop of radiant heat off of a steam boiler. I am looking at a job where this is what the architect has in the specs. I am not sure that this will work.

Any input is appreciated.

Thanks,
R. Griggs

Unknown

Takes more time

than 1 to 3 years to destroy the pump . I connected a baseboard zone to my sisters old Arco steamer , and this boiler was full of crud . I took the supply from a tapping about 6 inches below the water line , and the return goes into the steam return . No bypass piping ( hey , it's a freebie for my sister ) .

I put a valve on each side of the 007 for a quick changeout . Been over 10 years and still going .

Unknown

look at this article about this

http://www.bellgossett.com/Press/CounterPointJun04-B.pdf