J1 PROChilled water flow rate from cooling capacity
How to calculate chilled water flow from cooling capacity and temperature difference, with conversions between kW, refrigeration tons, L/s and US gpm.
Chilled water flow follows directly from the heat balance on the water: the heat the coil removes from the air equals the heat the water picks up.
The formula
ΔT is the difference between return and supply water temperature. 6 °C supply and 12 °C return gives ΔT = 6 K.
Quick reference
| ΔT (K) | L/s per kW | L/s per TR | US gpm per TR |
|---|---|---|---|
| 5.0 | 0.048 | 0.168 | 2.66 |
| 5.5 | 0.043 | 0.153 | 2.42 |
| 6.0 | 0.040 | 0.140 | 2.22 |
| 7.0 | 0.034 | 0.120 | 1.90 |
| 8.0 | 0.030 | 0.105 | 1.66 |
1 TR (refrigeration ton) = 3.517 kW. The familiar "2.4 gpm per ton" corresponds to a 10 °F (5.6 K) ΔT.
Choosing ΔT
A larger ΔT means less flow, so smaller pipes and pumps and lower pumping energy. But the coils need more rows, and the chiller has to supply colder water or accept a warmer return. Many modern projects use 6 to 8 K instead of the older 5.5 K. Whatever you choose, keep it consistent between coils, pipes, pumps and chillers, or the system runs with low ΔT and wastes pump energy.
Example
A 350 kW AHU coil with 6/12 °C water: Flow = 350 ÷ (4.19 × 6) ≈ 13.9 L/s (50 m³/h).
The J1 Pro CHW Flow calculator works forward and in reverse, and the Pipe Sizer checks velocity and friction.
Guides are for preliminary design and learning. Always verify final designs against project specifications, local codes and manufacturer data.