Cooling Tower Pipe Sizing
Cooling Tower Pipe Sizing
(OP)
I know that the rule of thumb when sizing water pipes in a cooling tower is 3 GPM per 1 TON for condensed water (i.e. return) and 2.4 GPM per 1 TON for chilled water (i.e. supply).
Who came up with these figures, and don't these numbers depend on Temperature differences anyway?
Who came up with these figures, and don't these numbers depend on Temperature differences anyway?





RE: Cooling Tower Pipe Sizing
Regards,
Brian
RE: Cooling Tower Pipe Sizing
If you plug 10 F in the equation 500 * GPM * DT and then divide by 12,000 you get 2.4 GPM / TON.
The heat of rejection out the condenser is greater then what is absorbed by the evaporator. For a water cooled chiller the total heat of rejection is 1.25 times the evaporator capacity. So when you say 2.4 or 3.0 GPM per ton you are reffering always to EVAPORATOR tons. 2.4 GPM * 1.25 = 3.0 GPM.
Most standard evaporators and condensers are sized using 2.4 GPM/TON (3.0 for condensers), 10 F DT, 9-10 F approach etc.
A given heat exahcnger has an infinite (within limits of course) number of capacities, therefore to give a given part a name it must be sizedd according to standard conditions.
Whether or not they apply to what you are doing is up to you to decide.
Clyde
RE: Cooling Tower Pipe Sizing
CHR (Btu/hr) = gpm x 500 x °F water temperature rise, or delta “T”
For 15,000 Btu/hr CHR per ton, and 10° water temperature rise, 3 gpm per ton is the required flow rate. Example: 15000btu/hr/500x10degrees = 15,000/ 5,000 = 3gpm
Now with closed circuit coolers(evaporator) operation of the system is calculated a little different because it’s based on a heat rejection of 12,000btu/hr, so using the same formula it becomes 12,000btu/hr/500x10 degrees = 2.4gpm. The extra 3,000 btu/hr in the condenser is a gain mostly from the heat of compression of the refrigerant in the compressor. Now you may ask where does the 500 number come from ,well 500 represents the number of lbs of water circulated in 1 hour or 8.333lbs x 60 minutes = 500 lbs. Hope this is helpful