Flow Rate of water

Dear Friends ,

Is there any standard formula to calculate the ideal flow rate of water in the condenser or chiller pipeline ? I have somewhat idea regarding the same but not sure.

I hope you will share your ideas.

Thanks for cooperation.

Hello sumit,
the majority of water chillers and water cooled condensers are based on 5.5'C temp rise.
Apply formula for water chilling ; Kw = 4.2 Kj/kg * temp rise [ 'C ] * flow rate in Litres per second.
Flow rate = Kwr / 4.2 / 5.5 'C example
160Kw r / 4.2 / 5.5 = 6.93 litres per sec.
Reduce the temp rise and flow rate will increase.

Dear Magoo ,

Thanks a lot for your reply. According to you , Flow Rate = KWr / 4.2 / Temp Rise. Can you please again explain me this formula , as i am not able to get the meaning of Kwr. I know what is temp rise , but please explain me other terms used in this formula. I will be thankful to you.

Kw refrigeration as opposed to Kw electrical

kw/ 4.2 x dt = kg/s or L/s for water

kw = energy absorbed through refrigeration
4.2 = specific heat capacity of water ( kj/kg )
dt = temp in and out ( k )

Hi Fridge ,

Thanks for your reply.

According to you , flow rate (L/S) = KW / 4.2 * dt.

But Magoo's formula was different , he said Flow rate (L/S) = KW/4.2/DT

Which one is correct ?

well the formula is derived from:

Q = m x cp x dt hence m = Q/ cp x dt

where Q = capacity in (KW)
m = mass flow rate ( kg/s or L/s)
cp = specific heat capacity ( kj/kg)
dt = temp difference (k)

so its a simple transposing of the original formula

Quote:

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Originally Posted by FRIDGE

well the formula is derived from:

Q = m x cp x dt hence m = Q/ cp x dt

where Q = capacity in (KW)
m = mass flow rate ( kg/s or L/s)
cp = specific heat capacity ( kj/kg)
dt = temp difference (k)

so its a simple transposing of the original formula

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Hi Fridge,
Thanks a lot for sharing the above formula about flow rate of water. I already have services to audit water leaks and techniques to detect them properly, but I want to know more about water audit services which can be helpful to save water and water bill. Can you tell me that this formula related with flow rate of water is useful or not to water audit services.
Please share your ideas and tell about other more water audit services to save water and cost money.

Thanks
Maire

Hello Sumit
The equipment specifications dictate which flow rates are necessary for the equipment normal functioning. Note that savings on water in this respect may lead to your lost of the equipment.

Hi Maire,

If by water audit you mean water treatment or rate of water lost, then this formula will not help. I have no experience in water treatment but regarding the leakage rate/ evaporation rate, i think it may be worth looking at the cooling tower drift eliminators. Over the years they deteriorate and allow more than the normal amount of water lost through evaporation and increase your water bill. Good water treatment can reduce this deterioration also.
I've heard of companies doing eliminators that can reduce the rate of water lost through evaporation in cooling tower. If you can reduce the rate of evaporation water loss without sacrificing the towers heat rejection capacity then you may make savings on your water bill.

Quote:

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Originally Posted by FRIDGE

Hi Maire,

If by water audit you mean water treatment or rate of water lost, then this formula will not help. I have no experience in water treatment but regarding the leakage rate/ evaporation rate, i think it may be worth looking at the cooling tower drift eliminators. Over the years they deteriorate and allow more than the normal amount of water lost through evaporation and increase your water bill. Good water treatment can reduce this deterioration also.
I've heard of companies doing eliminators that can reduce the rate of water lost through evaporation in cooling tower. If you can reduce the rate of evaporation water loss without sacrificing the towers heat rejection capacity then you may make savings on your water bill.

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Hi Fridge.....

Thanks a lot for the for such a kind and helpful reply..... I hope that might help me out some what...... Once again thanks a lot.....

Hello

Water is supposed to evaporate in a cooling tower, and the more, the better. To achieve the same effect without evaporation, one need to move more volumes of water, but by that more energy is spent on pumps.

If ,for instance, to keep a condensation T at a T a water condenser is designed for there is need for a definite amount of the coolant, one cannot be happy with an economy he/she has achieved on water on expense of the equipment life.

Hello Yuri B,

Yes you are correct, but you can make water savings by combining sensible and evaporative heat transfer.

http://www.baltimoreaircoil.be/BAC/EU/axidownloads20.nsf/activedocuments/115FF044BDFE4B49C125709D00537C2F/$FILE/BAC%20Intelligent%20Water%20Saving%20Products.pdf

anyway dont worry, i think the person who asked the question is actually trying to sell something on here ;)

Hi sumit,

In order to get flow rate of chilled water or condenser water for centralized chiller plant, there are 3 ways to do it:

1) By using flow meter - result: very accurate reading
2) By using formula or calculation of Chiller Capacity (Q = m x Cp x delta T) - result: not much accurate
3) By using pump (either CHWP or CDWP) performance curve. Once u get the delta Pressure (Outlet Pressure - Inlet Pressure), use the pump OEM to plot the flowrate reading - result: accurate

HI,

Thanks Yuri, Fridge , Maire and schiZOprEni for your replies. schiZOprEni , can you please explain the third method to calculate flow rate.After getting the delta pressure of pump, how can one plot the flow rate reading ? What is OEM.

Thanks for your cooperation.

Btu/hr
flow rate (us gpm ) = -----------------------------------------------------
500 x water temp out deg f - water temp in deg f

The more water flow is through the pump, the more work does its el. motor, the more ampers are consumed by it. You can look at what the pump (motor) maximal current is - by its maximal capacity, according to its specification - and what ampers the pump goes now with, then comparing you can see more or less what at this moment flow rate may be.

OEM = original/official engineering/equipment manufacturer

Hi Sumit,

Pump performance chart/graph is given by the manufacturer (OEM) once a pump is tested at their lab. It is just like a birth certificate. On the graph, there are two parameters Total Head (or delta Pressure) at the Y-axis and Total Flow Rate (USGPM) at the X-axis. As i said, once u get the value for delta Pressure across a Pump, then u can measure the liquid flow rate by plotting the point on the graph.

a easy way is by looking at your pumps info - min and max head. if it says e.g - 4.2 min and 6.8 max you can take on the middle i.e about 5.5 bar. Or they may say 42 headmin 68 head max just remember they mean 4.2 not 42 bar. Head is up. bar is flow. to commission these you may need to slow the head pressure or increase which may require a bypass. Plus make sure pump amps are right. There are a lot of graphs that are easy to read per manufacturer