# Thread: Water flow and Delta T

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## Water flow and Delta T

Had a pump guy in on a job yesterday. He was saying that if you have too much water flow through a chiller you delta T will be closer. Is that true?

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If by closer you mean decrease, the answer is yes. There is a very basic principle here that you may want to take the time to learn.

The tonnage of a chiller can be determined by the following formula: Tons = GPM X DELTA T / 24. For example, if you have a 100 T. chiller that is designed to produce a delta T of 10*F then the flow would have to be 240 GPM. 100 = 240 x 10 / 24. Using the formula, one can see if the GPM is increased then the delta T has to decrease to get the correct answer. The 24 is a constant and the tonnage isn't going to increase if the flow increases.

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The machine that i have is a 30 ton designed to do 10* t at 100% at 65.3 GPM. I am get a 9.7 delta T at 50 %. So does that mean i am flowing to much water? I have a pressure drop of 14.56 ft head the design is 12.6 ft head

4. Originally Posted by jeremyr325
The machine that i have is a 30 ton designed to do 10* t at 100% at 65.3 GPM. I am get a 9.7 delta T at 50 %. So does that mean i am flowing to much water? I have a pressure drop of 14.56 ft head the design is 12.6 ft head
at 65.3 gpm and 10F, you have a DESIGN LOAD of 27.21 tons. if you push more evaporator water through the barrel, then your chiller has to work harder to remove the same heat load at the same conditions because the water flows through the barrel faster and has less time to give up its heat. if you are getting a 9.7F drop at 15 tons, then you aren't flowing the same water as designed or something has changed from design. at 14.56 feet of head versus 12.6 feet of head, you are flowing about 8% more water. keep in mind that we are assuming that your design is water and that you have water in it now. other fluids (glycol, etc) change things dramatically.

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Check out bell and gossets system sizer app for smart phones,it can take design chiller barrell drops and calculate flow based on actual readings and also give tonnage

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Originally Posted by KnewYork
If by closer you mean decrease, the answer is yes. There is a very basic principle here that you may want to take the time to learn.

The tonnage of a chiller can be determined by the following formula: Tons = GPM X DELTA T / 24. For example, if you have a 100 T. chiller that is designed to produce a delta T of 10*F then the flow would have to be 240 GPM. 100 = 240 x 10 / 24. Using the formula, one can see if the GPM is increased then the delta T has to decrease to get the correct answer. The 24 is a constant and the tonnage isn't going to increase if the flow increases.
Where did you get the 240?

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Originally Posted by SanchezHVAC
Where did you get the 240?
Look at the math that was used. Multiples of 10 were used for the example, so he came up with 240 gpm.
If you know the gpm then you can figure tonnage. To find the gpm you will need the original spec. for the chiller.

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You can calculate the chiller Cv. That is done by dividing the design GPM by the square root of the design delta p. To obtain flow multiply the Cv times the square root of the measured delta p.

Another way is to get flow is to multiply the design GPM times the square root of the measured delta p divided by the design
delta p.

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I hope that picture came thru clear.

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Dang it fat fingers!

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God lord this is the picture . Ignore the others.

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Don’t forget only use one gage to take your readings. That takes gage inaccuracy out so you don’t chase your tail.

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Originally Posted by Chev5372
Don’t forget only use one gage to take your readings. That takes gage inaccuracy out so you don’t chase your tail.

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Thanks a lot! Especially the pics. How do you upload pics on here?

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