The capacity of the Cooling Tower (CT) can be calculated as follow:
Let’s say the capacity of the Chiller is 448.5kW. As per the selection sheet of the Chiller, the condenser water flow is 0.054 x 448.5 l/s = 24.219 l/s.
Let’s say the EWT and LWT of the CT is 35 and 29.5 degree centigrade.
So, the delta T (range) is 5.5. So, the capacity of the CT will be 4.2 x 24.219 x 5.5 = 559.46 kW = 160 TR So, the CT can be specified as follows: Capacity = 160 TR / 560 kW Range = 5.5 Approach = 1.5 (29.5 – 28)
Note: The difference between the Leaving Water Temperature from the CT and Wet Bulb Temperature is known as the “Approach”.
Thumb Rule: The capacity of the CT is 560 kW. The capacity of the Chiller is 448.5 kW. The ratio = 560 / 448.5 = 1.25 Generally, the CT is sized 125 – 130% of the Chiller capacity.
CTI certification: If a CT is to be CTI certified, then the APPROACH must be greater than 2.8 degree centigrade.
Another way of calculating the capacity of the Cooling Tower: kW/TR value of the chiller from the data sheet of the chiller = 0.8 So, the power input required for the chillers at the full load condition = 0.8*(448.5/3.517) kW = 102.02 kW Consider that 80% of the total power input will be converted into heat energy.
So, the heat energy produced = 0.8*102.02 kW = 81.62 kW. So, the total heat energy to be rejected = 81.62 + 448.5 kW = 530.12 kW = 150.72 TR. So, the selected capacity of the Cooling Tower is 160 TR.
