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  1. #1

    How to calc BTU usage

    I have a heat exchanger used for domestic hot water and need to calculate BTU usage for billing purposes. I have a supply and return temp sensor and a meter that pulses a dry contact every 100 gallons. I have these three signals tied into a programmable controller. The display needs to output the total BTU's consumed and will be reset each month so that a bill can be generated for BTU usage. Can someone help me out with this calculation? Thanks for your help.

  2. #2
    Join Date
    May 2003
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    Utah
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    It takes 1 Btu to raise 1 lb of water 1*F.

    One gallon of water weighs 8.33 lbs.

    So, if a train were leaving Chicago at 88 mph and travelled for 3.2 hours.......

    In other words, this now becomes a simple little algebra problem.

  3. #3
    Thanks for the quick response. So if I have 100 gallons of water come through the heat exchanger and have an average delta T of 12degF, my total BTU's would be gallons*8.33*delta T or in my case 100 gallons * 8.33 * 12degF for a grand total of 9996 BTU's?

  4. #4
    Thanks for the quick response. So if I have 100 gallons of water come through the heat exchanger and have an average delta T of 12degF, my total BTU's would be gallons*8.33*delta T or in my case 100 gallons * 8.33 * 12degF for a grand total of 9996 BTU's?

  5. #5
    Join Date
    Mar 2011
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    Louisiana
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    100 gallons in what time period? If that is flow in gallons per minute, then use this formula:

    Total Heat (BTU/hr) = 500 x GPM x ∆t (water)

    J

  6. #6
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  7. #7
    Join Date
    May 2003
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    JP,

    I thought that perhaps I was skating through without actually giving any advice...but OK.

  8. #8
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    Mar 2011
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    Louisiana
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    sorry JP, I am trying to watch that.

    J

  9. #9
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    Part of what I'm doing with these reminders is not to slap your hands and make you afraid to post advice openly, but rather, to get you to fill out the form and get your * as Bunny did.

  10. #10
    Join Date
    Jul 2002
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    NorthEast
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    811
    I am sure you know this already, but
    I have seen (professionals),
    and simple guys such as myself
    get themselves in alot of trouble,especially when they were providing
    sub metering.
    Make sure that your G.P.M. meter is designed
    for the ranges of pressures that your system deals with

    Yes our application engineers use the simple formula
    Q= 500 X 1.O8 X Delta T
    I installed a very nice pulse type G.P.M. meter , but
    the pumps were on time of day V.F.D. 's when the pressures Slightly fell
    below the meter's pressure range ,the G.P.M. readings became
    totally false.

  11. #11
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    Quote Originally Posted by cleancondenser View Post
    ...Yes our application engineers use the simple formula
    Q= 500 X 1.O8 X Delta T....
    1.08 for water? that parameter is for air.
    "If you pull one more stunt like you just pulled with Tommy, you won't have to get on a plane because I will personally kick your ass from here to Korea!" - Best of the Best

  12. #12
    Join Date
    Jul 2002
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    sorry about that

    q= 500 x GPM x Water Delta T

  13. #13
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
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    1,219
    With a flow meter that pulses 1X per 100 gallon it will not be accurate enough for billing purposes.

    The temperature can change rapidly as the flow cannot...You will need a better flow meter or a BTU meter...

    Use BTUH=Delta T *F X 500 X GPM

    The 500 comes from 8.33 pounds per gallon (for water) times 60 minutes (minutes to hours) times 1 (specific heat for water)...

    I seriously doubt your existing data is adequate in its present form. You really need an actual flow transducer to ensure accuracy.

    Hope this helps....

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

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