Redoing Boiler piping

Discussion in 'Boiler Forum' started by acmpcm, Jan 7, 2010.

  1. acmpcm

    acmpcm New Member

    Messages:
    3
    Location:
    new york
    Hi All, New to the Forums!
    I am in process of re-piping hydronic system. System is 10 years old gv-6 series 2 boiler ( 153,000 DOE). Currently p/s piping with boiler loop done in 1 in copper and t's spaced 12 in apart into secondary system. secondary is a 2 in copper manifold parallel system with 1 circulator for indirect domestic heater piped in 3/4 in circuit. there are 6 other space heating circulator loops supplying fin tub radiators. each circuit about 20,000 btu 3/4 in copper.

    problems are boiler short cycling frequently (average 4 min firing time) with a large delta t of 40 degrees. boiler set point is 200 degrees. otherwise system working well with plenty of hot water and comfortable room temps.

    new scheme will have boiler loop done in 1-1/4 in copper pipe. and keep the 2 in secondary manifold.

    Questions:
    1. should we go to 1-1/2 boiler piping and what is best distance between copper t's to secondary loop?
    2. should the indirect heater ( amtrol boiler mate whs- 60 ) be piped parallel into the boiler circuit or keep it in the secondary circuit as a separate zone. if put in boiler circuit should it have closely spaced t's or just parallel circuit? planning on using 1 in copper for this circuit.
    3. should the boiler mixing valve be removed or plugged (per technical bulletin) since it might fail and then add an external mixing valve to keep the boiler return water temp above 140 degrees. if so would a ball valve work from supply to return or do you suggest a mechanical or motorized mixing valve?

    4. with the short/frequent cycling can you suggest or recommend a buffer tank and size.
    Is this necessary? the multiple space heating zones are micro loading. the house is well insulated and zones do not run for more than a few minutes each and seem to always be running one at a time.

    5. it seems that the gv-6 is oversized for the house. house is 4500 sq ft in north east.

    6. what is optimum delta t and duration of firing time for this boiler?

    Thanks
    any help would be appreciated.
    this is the second re-pipe of this system. original plumber had circulators on return with all kinds of noise!

    Anthony
  2. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    The boilers "set point" is 200F? That's pretty hot and you could probably get away with a much cooler temperature of 165-170F. Plus you'd save a bit of coin on your gas bill.

    Now on to the questions:

    1. 6" center to center on each tee is a pretty good distance.

    2. I would pipe it in parallel off the main loop for sure.

    3. I would definitely recommend a motorized mixing valve to keep your temps exactly where you want em. This way if you have an outdoor reset or some other control fluctuating your main loop temp you're not having mixing valve issues bring the temps back too hot or too cold.

    4. I'd say try widening your set point differentials to about 145 and 180. Buffer tank size I would guess about 30 gal. If you have a run fraction of less than about 30% your efficiencies really drop off.

    5. Ok.

    6. If by this you mean the return temp vs supply temp I would say it depends a bit on how you have your system set up. 10-15F maybe though.
    Last edited: Jan 8, 2010
  3. cattledog

    cattledog New Member

    Messages:
    42
    Location:
    Portland, Oregon
  4. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Or, dump the primary secondary piping and go with a hydronic separator. Anyhoo. can you post a picture of what you have now?

    I would like to see the indirect piped off the secondary loop so that it does not create an intermittent drop in flow across the primary.

    I doubt you need a buffer tank but if you have the extra money it's not a bad idea.

    A three way zone valve, a tempering valve are needed to control return temperatures.

    Look into variable speed pumping also
  5. acmpcm

    acmpcm New Member

    Messages:
    3
    Location:
    new york
    Hi All,
    Thanks for the reply!

    Looks like this system has 2 problems, a pressure/ flow issue and a short cycling issue.
    I think i will re-pipe first and leave t's for a future buffer tank if needed. Hopefully with better flow things will improve. Looks like 1 1/2 inch off the boiler will be best, along with the closly spaced t's.

    The indirect hot water tank is on priority control. Can it be placed in the boiler loop?

    The video link was very helpful.
    I would post a picture but the piping is very embarrasing!

    Anthony
  6. acmpcm

    acmpcm New Member

    Messages:
    3
    Location:
    new york
    HI All,
    I am writing for follow-up and to thank all for the help!
    The system redo is complete. P/S close spaced Tees 1-1/4 pipe , 80 gallon buffer tank and Tekmar 260.
    The system works great! Instead of 2-3 min burn times I get 8-14 min depending how I set the diff on the Tekmar.
    System is quiet and very confortable.

    Last question. For best effiency is it best to:

    1-set a 40 degree diff with 160 target and get a 10-14 min burn time depending how many zones are open at the time. this gives a nice charge to the buffer tank with water temp going from 140-180 or,

    2- set a 30 degree diff with 155 target and get 8-10 min burn times. this way the water will be slight cooler with the 15 degree up and down from the target going from 140-170 with reset.
    thanks all for the help----Anthony
  7. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    aim for a 20 degree delta T between outlet and return let burn time be what ever it is.
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