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Chiller Tonnage Calculator (Flow × ΔT)

Chiller cooling capacity in tons of refrigeration, kW and Btu/h from chilled-water flow and supply/return temperatures (tons = gpm × ΔT ÷ 24), with glycol correction, power input and COP.

Units

Chilled water flow (m³/h or gpm)

Supply (leaving) water temperature

Return (entering) water temperature

Fluid

Chiller efficiency (kW per TR)

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How it works

US: tons = gpm × ΔT(°F) × fluid factor ÷ 24 (500 × gpm × ΔT = Btu/h; 12,000 Btu/h = 1 ton) · metric: kW = m³/h × 1.163 × ΔT(°C) × fluid factor · TR = kW ÷ 3.517 · power = TR × kW/TR · COP = 3.517 ÷ (kW/TR)

The cooling a chiller delivers equals the heat the chilled water picks up in the building: flow × specific heat × temperature rise. One ton of refrigeration is 12,000 Btu/h (3.517 kW) — the heat to melt a short ton of ice in a day. The common shortcut tons = gpm × ΔT ÷ 24 comes from 500 × gpm × ΔT Btu/h for water; glycol mixtures carry less heat per unit volume, so they need a correction factor or more flow. Comparing this field-measured capacity with the chiller’s electrical input gives its real kW per ton and COP.

Worked example

Chilled water flowing at 100 m³/h, leaving the chiller at 7 °C and returning at 12 °C (ΔT = 5 °C), carries 100 × 1.163 × 5 = 581.4 kW, or 165.3 TR (1,983,785 Btu/h). At 0.6 kW per ton the compressor draws 99.2 kW, a COP of 5.86 and an EER of 20.

Sources: Engineering ToolBox — Chilled water systems: capacity (gpm × ΔT) · ASHRAE Handbook — HVAC Systems and Equipment (chilled-water systems)

Frequently asked questions

How do I calculate chiller tonnage?

For water in US units, tons = gpm × ΔT(°F) ÷ 24. In metric, kW = m³/h × 1.163 × ΔT(°C), then divide by 3.517 for tons of refrigeration. 240 gpm at a 10 °F ΔT is 100 tons.

What ΔT do chillers use?

The traditional design is 44 °F supply and 54 °F return (10 °F, about 5.6 °C), or 7/12 °C in metric. Many newer plants use 12–16 °F (7–9 °C) to cut pump flow and energy.

How does glycol change the capacity?

Glycol has a lower specific heat than water, so the same flow and ΔT moves less heat: roughly 5–8% less at 30% concentration and about 16% less at 50% ethylene glycol.

What is a good kW per ton for a chiller?

Water-cooled centrifugal chillers run about 0.5–0.6 kW/ton at full load (COP 5.9–7), screw chillers 0.6–0.75, and air-cooled chillers 1.0–1.3 kW/ton including fans.

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This calculator is for educational purposes. Double-check important results before acting on them.