Chilled & Condenser Water Flow Rate

A Water-cooled Chilled Water System primarily consists of Condenser Water and Chilled Water loops


Sizing of header and pipes depends largely on the flowrate of water through the pipes. It is common for Engineers to estimate the Chilled Water and Condenser Water Flowrate based on their tonnage, as 2.4 usgpm/tonne for Chilled Water, and for Condenser Water, 3 usgpm/tonne.

This Rule of Thumb figures (Flowrate per tonne) don’t just appear out of nowhere. Theoretically, they shall be varied to changes in ∆T of Chiller and Cooling Tower, according to the formula below.

Q =mcθ

Q =mc∆T


Q        = Energy in Joules expanded to cool m kg of water at specific heat capacity c J/kg-1°C-1 by ∆T °C

m        = Mass of Water, kg

C         = Specific Heat Capacity of Water, 4190 J/kg/ °C

θ          = ∆T = Difference between Entering and Leaving Temperature of Chiller/Cooling Tower, °C


This calculator estimates the value of the flowrate per tonne (Rule of Thumb) figure for Chiller & CT flowrate based on Delta T in the formula above. It also calculates the flowrate of Chilled water or Condenser Water Flow rate based on the computed usgpm/tonne and tonnage of the waterside equipment.

Flowrate = Flow (usgpm)/Tonne x Tonnage of Chiller/Cooling Tower

After the flowrate (usgpm) for the CT and Chillers’ pipes and headers are obtained as shown above, pipes and header sizes can be calculated by manipulating the allowable velocity (fps).

Generally accepted velocity of water for different segments of chilled and condenser water pipes is shown in the tabulation below.


At the adopted velocity, pipe sizes can be determined from the tabulation below.




1: Calculating Flowrate per tonne (usgpm/RT)


Chilled Water Flowrate: 2.4 usgpm/RT


Condenser Water Flowrate: 3.0 usgpm/RT

2: Calculating Flowrate (usgpm)


3: Sizing Pipes and Headers based on estimated Flow Rate


Pipe Sizing based on adopted fluid velocity:


A downloadable Excel File for Chilled & Condenser Water Flow rate per tonne (& flow rate) is available below.

Chilled & Condenser Water Flow rate Calculator (Excel)