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    Indirect and boiler sizing (5 Posts)

  • Bart Vaio Bart Vaio @ 5:22 PM
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    Indirect and boiler sizing

    Can someone help me with a reference for indirect sizing.  My project has a total heating load of 128,000 btu across 11 zones.  I had specified a Lochinvar whn-155 boiler coupled to a triangle Tube SME 120 multi energy tank.  We were planning to use the outer shell of the SME as a buffer tank for the radiant micro loads (each bath room is zoned)  and using outdoor reset from the tank with a Taco I valve for reset. the inner (domestic)  tank is 105 gallons, jacketed with 66 gallons of heating water.  A consulting engineer said that my radiant boiler sizing was correct but stated that my load for domestic hot water was 150,000btu additional for the 4 bathrooms.  I know I have to account for the Domestic load but that is a fractional load right?  I know on the coldest design day the boiler will be running a 75% of capacity all day load but nobody takes a shower in all 4 bathrooms all day long on the coldest day of the year.  His specification will have my boiler 100% oversized.  Any help would be appreciated.

  • kcopp kcopp @ 5:51 PM
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    If your boiler.....

    is in theory already over-sized then forget about it... you have the storage, you will not run out of hot water. What is the place you're heating? I have 3 baths a SSU-60 and a Buderus 115-21 (3 section) w/ tekmar 260 AND  2-3 teenagers and I never have run out of hot water in 8 yrs.
  • Bart Vaio Bart Vaio @ 5:56 PM
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    Sorry, to clarify. This is a new installation on a new structure, new radiant floors etc. the point is I always size my equipment properly for the best efficiency, I hate massively oversized mod con boilers, it irks me to put my name on a system I know is oversized. This is a large custom home.
    This post was edited by an admin on February 15, 2013 5:57 PM.
  • kcopp kcopp @ 11:56 PM
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    no matter...

    new or old. You don't figure in the domestic load to the boiler sizing UNLESS you have some CRAZY hot water needs.
  • Chris Chris @ 8:48 AM
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    Indirect Capablility

    Looking at the specs depending on temp rise this is what it produces

    70 Degree Rise (50 degree incoming 120 setpoint)
    333 Gallons Per Hour or 5.5gpm

    5.5 x (70x 500) = 192,500 Btu/hr needed

    90 Degree Rise (140 set point)
    220 Gallons Per Hour or 3.6gpm

    3.6 x (90x500) = 162,000 Btu/hr

    That is the continuous rating. Add the 105 of storage to gph for 1st hour recovery.

    He wants

    300,000 /45,000 = 6.6gpm for a 90 Degree Rise
    300,000 /35,000 = 8.5gpm for a 70 Degree Rise

    We don't know what's in those 4 showers so can't tell whose right or wrong.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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