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Best small ECM pump to handle condensate

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With all the discussion of system efficiencies below, I thought I would see if I can upgrade the efficiency of condensate pumps and boiler feed pumps. Since the sizing factor ends up requiring such a large pump that needs to cycle and be throttled in most cases, I want to set up a 2 stage operation where a small pump could provide the return rate needed for continuous firing and the second stage pump be set up to meet start up needs and meet code requirements. For the 4, 700,000 input boiler I'm looking at, all I need is 8 GPM at around 10 feet of head at most. This could easily be covered with a small residential circ. So only around 85 watts for a standard pump, but it would be nice to see if I can get that down to 40 watts with an ECM pump.
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Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,623
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    I wouldn't use a wet rotor if that's what you are considering
    Solid_Fuel_Man
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,218
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    I'm just wondering what people have seen out there. I know wet rotor isn't the best, but on the systems we regularly maintain, the water stays quite clean throughout the season due to few leaks and water treatment. We often come back the next season for service and the water is still light pink and almost clear in the gage glass. Takes a while to get it there, though.
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  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    I would be worried about startup torque with a wet rotor circulator. Steam is still an open system, but it sure would be worth the experiment. Reliability would be top priority with condensate return. Do you have high level floats to either shut down the boilers or I guess your second stage pump? I'm a HUGE fan of 3 phase motors for any place where 3 phase is available. Even fractional HP 3 phase motors.

    Our discussion was focused on language used, real world with 4 boilers of 700,000 input the condensate pump is a drop in the bucket.

    I wish any of the steam systems I work on we had anything close to clearish water! No one wants to spend the time on them (or pay for it).
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • archibald tuttle
    archibald tuttle Member Posts: 1,085
    edited July 2019
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    interesting. @EBEBRATT-Ed are you worried about startup torque or water quality or . . . with a wet rotor? The biggest problem i've seen with these pumps in hydronic service is corrosion in cast iron pump bodies. So maybe you could go brass or stainless (all these anti-lead people drive me nuts, you used to be able to get a brass circulator pretty reasonable and actually if you use a pipe thread or G union circ the stainless ones aren't that bad.

    I'm trying to think of the condensate tanks i maintain and whether there is a low pipe tap you could use for something like that. And maybe a strainer . . . although the condensate itself, at least in one old system i've been able to observe by replacing condensate drop with clear polycarbonate is clean as a whistle, which, ironically given all the instant corrosion revealed between steel and steam at any point in the system, forgets that circulating condensate is pure water by definition (maybe a little slug of junk at the front if you've got wet steam but i guess that is always a first problem to solve anyway.)




    I guess it is possible as returns corrode on the inside that you would get some source of corrosion particles in the condensate stream but this system is no youngster and you can barely see the condensate stream and waterline in the picture - not only because of the lack of focus, sorry its a snap out of video and not super clear but the waterline is just below 46" and you can see the clean condensate trickleing down the wall of the clear pipe in small chaotic rivulets above that. Maybe the tank itself will add some corrosion but the condensate itself after running through some 85 or 95 year old returns looks pretty damn good.

    Now that the subject is brought up, this whole condensate return concept seems to be based on slugging and every pump i've seen is a 'giant' and will slug the whole tank full back into the boiler in like 15 seconds which interrupts steam production. i can watch the steam pressure fall in half of more (from a low start) when the condensate pump goes off. Not sure this is inherently 'bad' but i don't think it is particularly 'good' either and if you are running tight vapor control its going to seesaw controls a bit around setpoints. It seems like a far more ideal approach would be a hard/strong start ECM variable speed that can be tuned to match the condensation rate. Of course if steam were hydronic we would already have such stuff being manufactured but the lack of ubiquity means low unit sales . . . so we have to figure it out ourselves. So maybe you would need a float with a modulating signal instead of an on/off differential or some way to measure the rate of condensate influx and just leave the float as a safety off so you don't run the pump dry.

    Or maybe you could just dump the condensate into a 5 gallon bucket for an experiment and get a flow rate (maybe against a couple different indoor and/or outdoor temps) and use those as parameters to size or meter an ECM pump. From my clear pipe experiment, I didn't notice a particularly big early slug. My guess is that because the radiators always are getting steam at different times/rate that by the time the slowest rads are sending startup slug the others have evened out so it isn't as big as theory might suggest.

    Of course another possible way to deal with a big condensate pump is to consider whether you actually need a condensate pump . . . This clear return experiment I set up was to emperically test gravity return against theory on an 800,000 single boiler for 6 apartments where the new atmospheric boiler installed maybe 20 years ago had a water line way lower than the original snowman, and my guess is it didn't even really need a condensate pump with the original boiler. But the 'techs' just put in a new one with the new boiler cause it had one before. (actually, i'm not absolutely sure it had one before cause I never say the earlier system and looking at where their piping joins the original you can't tell for sure. Maybe they just put one in because this was a small commercial sizing and they anticipated operating pressures in pounds rather than ounces (At full fire, i can't even get the think over a pound if i try, but I digress.)

    This won't tell you anything about your system but if you like plumbing porn i posted this test on the wall earlier . The biggest bit of work was to pull the steam trap replace it with an end vent for the return and set up a 1" gravity based gifford loop as a test. There are actually 6 returns, one for each unit in this building so i just used one to test and was able to make a gifford loop into a tee on an equalizer without too much trouble.

    You might know from obvious cues that you are running too close for comfort on such a switchover, but i was literally running only 5" above the boiler in this gravity return with normal operating pressure in this system which i have taken down to around 8" WC. A lot of these pumping systems presume a much higher system operation pressure. So I spent some time pulling the operating pressure down and making sure that it did as well emperically as it should in theory before i moved to the test for eliminating the pump. When all was said and done I have 30" of reserve A/B distance so even if the boiler was running up to 1 lbs would be no problem. (I didn't, and kick myself in the 'next time' vein, test the pressure at the end of the return. the emperical results suggests I had about 2.5" steam pressure remaining and by the nature of having a steam vent at the end of the return , you aren't really going to be to a zero inflection point so you aren't even fighting the whole pressure at the boiler - albeit for operating margin I absolutely wanted to have enough drop to over come the highest possible boiler operating pressure with 0 in the return.)
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,218
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    I believe there are continuous feed systems out there.... ,my Shipco rep has spoken of them. I agree that the power draw from condensate return equipment is a drop in the bucket compared to the power draw of all other systems, but it is still very inefficient...large pumps cycling on and off with standard motors. Some of the power burner manufacturers are starting to use ECM motors, so at least that inefficient power usage is being addressed.
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  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Typical ECM motors are around 70-80% efficient. A standard 3phase induction motor is 80-90% efficient.

    The dramatic savings from ECM comes from it replacing PSC motors common to our industry of fractional HP motors. 3 phase always wins (if its available) and is stone cold reliable.

    Problem is that manufacturers dont want to sell equipment with 3 phase motors as it limits their sales or makes them have more part numbers for single and 3 phase.

    3 phase motors are also cheaper to buy than their equivalent single phase counterparts due to fewer moving parts, generally speaking.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,218
    edited July 2019
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    Thanks for that enlightenment. It's been a long time since my engineering classes and they were "engineering lite" for architects. I suspect the problem would be finding 3 phase 1/25 hp pumps that would be needed for these low flow rates.
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  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,623
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    @The Steam Whisperer,

    3 phase is always better. Self starting. Engineers used to spec anything larger than 1/2hp to be 3 phase don't know if that is still the case. 3 phase always lasts longer. Don't think you could find 3 phase in 1/25 hp. Power plants use continuous feed all the time. Boiler feed valve are modulated by a modulating pump controller. MM makes them, can't recall the model #. Pumps run all the time.

    @archibald tuttle, yes water quality with a wet rotor would be my concern
  • hot_rod
    hot_rod Member Posts: 22,259
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    ECMs are DC motor and supposed to have better starting torque compared to the small PSC small circulators.

    Armstrong has small non wet rotor circs available.
    http://armstrongfluidtechnology.com/en/products/design-envelope-compass-r-circulator

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,218
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    1/6 HP is about as low as they seem to go in dry rotor pumps. Is that armstrong pump an ECM design?
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