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solar nut

solarnut Member Posts: 6
sizing the DHW for a 54 unit apt.building using 37 gal/apt/day usage and figuring a delta T of 85F

so 54 X 37 X 85 X 8.34 = 14,163,822.2 BTU needed/day

ok now Seigenthaler in his book Modern Hydronic Heating p634 used a peak load of 11.6% of the time

so taking a round # of 15%

14,163,822 X 0.15= 198,293.5BTUH X 85% efficient boiler gives

198,293/.85= 233,286 BTUh

so a 270,000 BTU boiler with two 119 gal storage tanks as a buffer should be able to handle the DHW load.

Am I correct or can someone tell me why this reasoning is faulty???


  • Zman
    Zman Member Posts: 7,372
    Gallons per day

    You are doing the math correctly.

    I would be careful of the gallons per day number. What is the flow rate at the shower?Is it new construction?

    It is interesting that Siggy does not discuss the relationship between production and storage. This link has some useful info.


    I suspect your numbers are a bit low.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • ColoradoDave
    ColoradoDave Member Posts: 54

    Not sure how you figured this usage number.... so I'm not saying it's wrong.

    However, I've been led to believe that 20g DHW per person is the typical usage.  The problem is, I can't remember where I saw it documented or if it was something in conversation.

    That being said, if you went with 20g/day/occupant... you'd have to estimate the average occupant load per apartment.
  • ColoradoDave
    ColoradoDave Member Posts: 54
    Correct Math

    Your math is correct... the 270k BTU boiler can handle the 2 119 gallons dhw tanks.  Especially if you plumb the two tanks in parallel on the domestic side, so the domestic water is drawn evenly through the two tanks.

    The question I cannot answer is if the load of 37g/day/apt is good, but if thats a standard across the county, it sounds like you're good to go.
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