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Indirect and boiler sizing

Bart VaioBart Vaio Member Posts: 55
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.



  • kcoppkcopp Member Posts: 2,744
    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 VaioBart Vaio Member Posts: 55
    edited February 2013

    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.
  • kcoppkcopp Member Posts: 2,744
    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.
  • ChrisChris Member Posts: 3,056
    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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