# Thread: How to calc BTU usage

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## 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. 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.

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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?

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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?

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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

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Bunny and Jarreau.

Please remember that this is also the AOP section, even if it isn't Residential.

7. JP,

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

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sorry JP, I am trying to watch that.

J

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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. 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. Originally Posted by cleancondenser
...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.

q= 500 x GPM x Water Delta T

13. 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

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