Chiller Tonnage Calculator
Calculate chiller cooling capacity in tons of refrigeration from chilled water flow rate and entering/leaving water temperatures.
Results
What is it?
Chiller tonnage measures cooling capacity. One ton of refrigeration = 12,000 BTU/hr � the amount of heat needed to melt one ton of ice per day. The standard chilled water design uses a 10�F delta-T (54�F entering, 44�F leaving). This calculator uses the fundamental heat transfer formula Q = m�Cp�?T, where 500 is the combined constant for GPM and water's heat capacity.
How to use
Enter the chilled water flow rate through the chiller evaporator and the entering and leaving water temperatures. The calculator outputs cooling capacity in tons, BTU/hr, and kW, plus the GPM-per-ton ratio which helps assess chiller and distribution efficiency.
Example scenario
A chiller produces 120 GPM at 44�F from 54�F return (?T=10�F). Capacity = 120 � 500 � 10 = 600,000 BTU/hr = 50 tons = 175 kW. GPM/ton = 120/50 = 2.4, which is exactly the ASHRAE design standard of 2.4 GPM/ton.
Pro tip
ASHRAE recommends 2.4 GPM/ton as the design standard, yielding a 10�F ?T. High-?T chilled water systems (12�16�F) use only 1.5�2.0 GPM/ton, dramatically reducing pump energy. However, high-?T requires careful coil selection to prevent stratification. A common commissioning finding is excessive GPM/ton (low ?T) indicating poor distribution control.