Chiller Tonnage Calculator

What the chiller tonnage calculator does

A chiller removes heat from a fluid loop or a process, and its size is quoted in tons of refrigeration, where one ton removes 12,000 BTU per hour or 3.517 kW. The chiller tonnage calculator finds the heat to remove from the flow and temperature drop of the chilled fluid, or from the mass flow, specific heat, and cooling range of a product, then adds a safety margin to give the chiller size to select.

Chiller tonnage formula

The cooling load is the mass flow times the specific heat times the temperature difference:

For water in US units this reduces to the familiar rule:

Glycol mixes have a lower specific heat, so the calculator uses their own density and specific heat. The chiller size is the load times (1 + safety margin).

Chiller tonnage example

A chilled water loop circulates 50 gpm and the water returns at 55 °F and leaves the chiller at 45 °F:

With the exact water properties the load is 20.88 tons, 73.4 kW, or 250,554 BTU/h. Adding a 20% safety margin gives a 25.1 ton (88.1 kW) chiller.

How to use the chiller size calculator

Choose US or metric units and the calculation. For a chilled water loop, choose the fluid, then enter the flow and the temperatures going into and out of the chiller evaporator. For a process chiller, choose the process option and enter the product mass flow, its specific heat, and the temperatures it must cool from and to. Set the safety margin, often 10 to 20%. Press Calculate.

Reading the chiller capacity calculation

The required chiller size is the nominal capacity to look for at your leaving water temperature. Chiller ratings are usually quoted at 44 or 45 °F leaving water and a set condenser condition; colder water, glycol, high ambient temperature, or altitude reduce the real capacity, so check the manufacturer derating tables. A margin that is too large wastes money and makes the chiller cycle on and off at low load.

When to use chiller sizing

• Process chiller sizing for plastics molding, food, and laser cooling
• Checking chiller tons for a building chilled water loop
• Converting gpm to tons from a measured flow and temperatures
• Sizing a glycol chiller for low temperature work
• Comparing chiller capacity in kW and tons of refrigeration

Common chiller sizing mistakes

• Using the pump flow but a wrong delta T. Measure both temperatures at the chiller.
• Ignoring glycol. It lowers capacity at the same flow.
• Oversizing heavily. A large margin causes short cycling.
• Forgetting pump and piping heat. Add them to a process load.

Tips for chiller tonnage

• Check the chiller rating at your leaving temperature and ambient.
• Use a buffer tank on small loops to reduce cycling.
• Log flow and temperatures to confirm the real load.

Related cooling tools

For comfort cooling by floor area, the AC tonnage calculator estimates the tons for a room or house. The heat load calculator adds up people, equipment, and area loads.

Process chiller sizing from the product load

For machines, the heat often comes from the product rather than from a known water flow. A molding machine that cools 2,000 lb/h of plastic, or a jacketed tank that cools a batch, sets the load through mass flow, specific heat, and temperature range. Add the heat of the pump, the piping gains, and any heat from hydraulics. When the load comes from a room or building rather than a process, the heat load calculator and the AC tonnage calculator are the better starting points.

Chilled water flow and the temperature difference

For a given load, a larger temperature difference means less flow, smaller pipes, and less pump energy; a 10 °F (5.6 K) drop is the classic design value and 12 to 16 °F is common in newer plants. The flow for a chosen temperature drop follows from the same formula, which the hydronic flow rate calculator solves for pipe sizing in a heating or cooling loop.

Chiller tons from gpm at a 10 °F temperature drop

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