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Do I need a feed pump?

ratio
ratio Member Posts: 3,332
Ok, currently Peerless 211A, 36752 ft steam, originally some giant cast iron behemoth from the 50s, pumped returns from the get-go. Two story parochial school, no basement, buried returns. The returns are starting to rot out, spent $lots to repair a few leaks. We just started a treatment program, I'm hoping to keep the returns from deteriorating further.

The condensate is slow to return, for whatever reason. From a cold start to operating conditions then say a WWSD, after all the water returns the level will be just over the top of the sight glass. It may be a case of not enough volume to begin with.

I can't tell for sure how it was originally controlled, but the current control scheme is to keep 2 lbs on when we're in heating season, so the over filling might not be a real issue, except that I had a thaw-out last year when we overfilled & put 2 in wc on the vaporstat! (steam -> water HX on an addition). Appx 50-75% of the emitters are controlled by pneumatic stats. Like I mentioned before, several major leaks were fixed over the summer, so we aren't feeding as much as before. Is there anything else that's important to know?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    You may well need a feed pump with that set up -- but rig it as a boiler feed pump (controlled by boiler water level) not as a condensate return pump (controlled by the level in the condensate receiver)! Then add makeup water -- if you ever need it -- based on the level in the condensate receiver -- and provide enough headroom in that receiver to accomodate any possible overfills... or provide an overflow.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 15,755
    If you're running that level of steam pressure to feed that HX, do yourself a favor and put in a separate hot-water boiler for the addition. You're wasting a lot of fuel with those standby losses.

    We had a church where the steam system had seven zones and whoever installed the boiler wired it to maintain 5 PSI all the time. You could have put a sauna in that boiler room without needing a dedicated heat source. We converted the burner to lo-hi-lo firing and rewired the zone controls so the burner would only run on a call for heat, and they saved 35% on their fuel during milder weather. Now the boiler only reaches 2 pounds or so.

    If you can limit the steam pressure, the condensate would return more quickly and you might not need a pumped return.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    SWEI
  • ratio
    ratio Member Posts: 3,332
    Jamie, I've already got a condensate pump, from the original design. I will need make-up water, as the chem kit checks tds by flowing water through the blowdown on the fill valve. We're making up with softened water now. Also, it's almost certain that we're going to loose another underground condensate line some time. The fill valve is the only thing that kept heat on in the building the last few years, I can't take the chance of leaving it closed. I do have a meter on it now, at least.

    Steamhead, it's a goal of mine to turn down the pressure as low as she'll go - eventually. I'm working on so many issues with this system that right now I just want to get her back to design spec, & then start tweaking for efficiency. One of my planned changes is a two-stage gas valve, but that's going to have to wait until we're out of the heating season, as I'd like to re-size the gas line for minimum drop. (As opposed to maximum drop. Sigh)

    Will I be better off turning the vaporstat down now? I'm a little worried about no heat at the furthest emitters when running at less than 2#s. AFAIK, the system was designed for 2#. I should be able to get to 16 oz in cutout, but I haven't been able to get closer that 10-12 oz in differential on the new 'stat.

    I think I need to keep steam up because all the classrooms are heated by big honkin' wall radiators controlled by pneumatic valves with wall stats. There isn't an easy way that I know of to control 'the system' that will respond to temp in the classrooms that doesn't involve lots of remote sensors that will basically duplicate the operation of the pneumatics.

  • Steamhead
    Steamhead Member Posts: 15,755
    Any chance this was once a vacuum system?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • ratio
    ratio Member Posts: 3,332
    Highly doubtful. 1950s build. Natural gas out of the gate I believe. Very oddly sistered to a boiler in the church that went in after the school bldg, which wasn't/isn't (mothballed in place) serving the church bldg at all. I don't understand it at all. Want some pics?
  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    A pump is a pump is a pump... it's how it's controlled that makes it a condensate pump vs. a boiler feed pump. The reason I prefer boiler feed pumps is that they are controlled by the boiler water level, and will never over fill the boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ratio
    ratio Member Posts: 3,332
    Right. What I'm up against is that the condensate receiver is in a small pit, & I don't think it's large enough to use as a feedwater receiver - it's 5 gal tops at 100% full. I'd have to add a larger receiver to pump into, & another pump to push the water into the boiler.

    Maybe the pit can be enlarged & the receiver changed out. Hmmm... Have to think about that. The condensate piping around the receiver isn't all that stellar anyway.