Condenser Make Up Water

[samoja]

Hello,

I am working on sizing pipes for Chiller condenser make up water. In whole process I have trouble figuring out how much water will be required for make up.
I assume that everything that evaporates will need to be make up, but how can I determine how much water evaporate.

Thanks

 

[ChrisConley]

Maximum make-up water will occur at your design heating conditions.

You should be able to find out using psychometrics how much water is being evaporated based on cooling tower tonnage.

Q = 0.68 * CFM * deltaW.

Q = tonnage of cooling tower

CFM = airflow of tower

deltaW = Summer Design conditions Humidity Ratio - Saturated Design Conditions

DeltaW will give you lbs of water, which you should be able to take over to a flowrate.

Having said all that, I'm sure someone has a rule of thumb formula which would be much faster.

 

[imok2]

Approximately 1,000 BTU’s are required to evaporate .12 gallons of water. Therefore, every tower ton (15,000 BTU/hr) requires approximately 1.8 gallons of water evaporation, or .03 gpm/ton.

As water evaporates in a cooling tower system, the water vapor enters the atmosphere while any dissolved solids remain behind, building concentration in the remaining water.

Most water treatment systems control this concentration by bleeding off the high concentration water, which is made up by fresh city water with a lower solid concentration. The amount of water that is bled off by the water treatment system is usually less than or equal to the amount of water that evaporates.

Therefore, the maximum normal water makeup
for a cooling tower system is .06 gpm / ton,
or about 2% of the nominal tower flow rate.

 

[cry22]

Depends on what you are looking for.
if you want to size the make-up pipe to the sump, go to the maintenance data on BAC cooling tower catalogue, it calls for 3 GPM/100 ton as a rule of thumb (that's of 3 rules listed there).
Call your local rep.
Now if you want to figure out how much water is consumed in a day, then you need to account for blow down in addition to evaporation.
Consider metering the make-up and the blow-down to get credit for sewage bills.
Some maintenance folks I talked to like to have a 2" quick-fill line in the water make-up to fill the sump quicker after a blow-down, so they want a 2" even if a 1" make-up does the job.

 

[HVAC68]

Thumb rule :

Condenser water flow = Flow through cooling tower = 3 to 3.5 USGPM / TR.

Approximate make-up water requirement = 1% to 1.5% of the water flow.

For a 1000TR plant, flow would be around 3500 USGPM and hence 52.5USGPM make-up. For a 12-hour plant operation, 52.5 USGPM x 12 x 60 = 37,800 US Gallons.

Decide how many days of storage you want to keep and size the tank accordingly.

The above figures are "Thumb rule" numbers and can be further fine-tuned by actual data obtained from the chiller supplier and cooling tower supplier.

Good luck



HVAC68

 

[KiwiMace]

~2% of condenser water flow, allowing for evaporation, drift loss, blow down.

 

[RossABQ]

While there are several rules of thumb based on thermodynamics of the process, in practice you cannot accurately estimate the requirements without knowing the detailed analysis of the make-up water. If it is full of minerals, you can't achieve high cycles of concentration.