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How to Calculate BTUH's with CI rads at 110 degrees?

JUGHNE Member Posts: 11,021
One of my old schools is scheduled for demo.
1932 2 pipe steam heated building.

It has about 39 CI rads totaling about 3780 EDR.
All 2 pipe top inlet and lower outlet.

I was considering salvaging some to heat part of our diesel power plant.
The largest engine is being removed and they have lost a lot of heating mass.
The proposed replacement would not heat the room while on stand by.

This place is on stand by 95% of the year and a 199,000 Munchkin is now heating the cooling jackets on 3 other engines. Water temp for this is 110 degrees.

This section of the building is 34' X 12' with 18' ceiling.
The 34' length has one side open to heated building.
All masonry floor and walls. 2 large doors and one large window.
Ceiling/roof may be R-19 foam under EDPM roof membrane.

The main question so far is: BTUH's per EDR at 110 degrees?

Need to maintain 50 degrees at -10 design.


  • Ironman
    Ironman Member Posts: 7,341
    edited October 2021

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    EBEBRATT-Ed Member Posts: 15,300
    edited October 2021

    I came up with around 72,000 load. Not much more than an educated guess.

    At that rate you would need 2400 edr

    7.2 gpm/20 degree TD
    JUGHNE Member Posts: 11,021
    Thank you Ed, so 30 btuh per EDR at 110 degrees.
    BTW, I had mis-typed the size of the room it is 19' wide not 12'.
    Not a great difference.

    I went back to see how I sized the Munchkin to begin with; it was a WAG with 4100 sq ft (16-18' ceilings in a 1920-30's building) of the entire building X 45 per foot = 184,500.
    The 199,00 would put out 183,000 btuh.....and being the largest mod con available it was chosen. (gas piping provisions were made for a 2nd one if needed).
    But one has done the job since 2003....not bad longevity for early Modcon (or any for that matter).

    To back into the method of the original guesstimate I have 34' x 19' = 646 X 45 btuh = 29,070 btuh.

    29,070 btuh / 30 btuh EDR = 969 EDR ( 969 / 80 = 12 rads)

    To put things in perspective, the "radiation" removed was a 32E Fairbanks & Morse diesel that the engine alone weights 70,000 lbs....yes 35 tons of iron heated to 110 degrees thru it's cooling jackets on the 6 (13") cylinders, heads and exhaust manifold, and BTY it holds over 200 gallons of lube oil.

    So you start the Munchkin early in the season.

    Using your 72,000 heat loss needing 2400 EDR and averaging 80 EDR per rad, I need about 30 rads.

    So if I threw the dart at the 100,000 heat loss then I would need 3333 EDR of cast iron.
    So averaging 80 EDR per rad I would need 41 rads.

    It will depend upon how much room we have.
    Might have to jack up the temp of the system.
  • mattmia2
    mattmia2 Member Posts: 9,404
    You could plumb the radiators separately and add a mixing valve and run the radiator at a higher temp than the engine blocks. Probably cheaper than adding that much extra plumbing for the needed radiators for 110(although it would be a great buffer tank and would let the whole thing coast through the coldest peaks for quite a while.
  • JDHW
    JDHW Member Posts: 71
    Would it hurt running the generator jackets a bit warmer so that you don't have to bother with another pump and a mixer.

    For radiators and outputs I like https://www.engineeringtoolbox.com/heat-emission-radiators-d_272.html
    It is all in metric but it does let you play with temperatures and flow rates and see the effects.
  • hot_rod
    hot_rod Member Posts: 21,820
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream