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A chiller removes heat from a water loop. The heat carried equals flow times temperature drop times the fluid factor (500 for water in GPM and °F). Dividing by 12,000 BTU/h converts to tons. Design flow is usually set so the loop runs about a 10°F drop.
- 100 GPM, ΔT 10°F.
- Tons = 100 × 10 ÷ 24 = 41.7 tons.
- Next standard = 45 tons.
Reference tables
Flow per ton at common ΔT
| ΔT (°F) | GPM/ton |
|---|---|
| 8 | 3.0 |
| 10 | 2.4 |
| 12 | 2.0 |
| 16 | 1.5 |
A number the tables do not give: at a 10°F drop, 100 GPM is about 42 tons — so plan roughly 2.4 GPM per ton.
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FAQ
Where does the 24 come from?
500 lb/h per GPM (water) × ΔT gives BTU/h; dividing by 12,000 BTU/h per ton leaves ÷24.
Water or glycol?
Glycol changes the fluid factor (lower specific heat and higher density), so the 500 constant drops — correct it for the mix.
Why a 10°F design ΔT?
It balances pump energy against pipe size; a bigger ΔT means less flow and smaller pipe but a colder supply.
Tons vs kW?
1 ton ≈ 3.517 kW of cooling. Multiply tons by 3.517 for a metric capacity.
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