Coolant Chillers
Sizing your Coolant Chiller
- Determine the total volume (gallon) of coolant in the sump and coolant loop. Be sure to include all the coolant in the system (extra tanks, filter, pump reservoirs, etc.)
- Measure the temperature (°F) of the coolant in the sump before machine start-up.
- Measure the temperature of that same coolant at one-hour intervals for three hours after start-up while the machine is operating at full capacity. Calculate Δ°F/Hr for each interval.
- Take the hour interval with the greatest temperature change and use the following formula to calculate the Heat Load (BTU/Hr). The chiller should have a suitable capacity to remove this heat load.
BTU/HR = Gallons of Liquid × Δ°F/Hr × Liquid Weight (lbs/gal) × Specific Heat of Liquid
Min. Recommended Chiller Size = BTU/HR × 1.20 (20% Duty Cycle Saftey Factors)
Example: For a machine with water-soluble coolant and a coolant tank of 56" x 30" x 11" tall (coolant level 8"). Maximum temperature rise measurement is 19°F during hour #1.
- Volume (gallons) = (56 × 30 × 8) ÷ 231 = 58.2 gallons
- Heat Load (BTU/Hr) = 58.2 gal × 19°F × 8.3 lbs/gal × 1.0 BTU/lb/°F = 9178 BTU/Hr
- Minimum Chiller Size = (9178) × (1.20) = 11013 BTU
Rules of Thumb:
| Liquid Weight | Specific Heat | Std. Chiller Capacities |
|---|---|---|
| Water based coolant: 8.3 lbs/gal | Water based coolant: 1.0 BTU/lb/°F | Small: 12000 BTU / 18000 BTU |
| Cutting Oil: 7.8 lbs/gal | Cutting Oil: 0.5 BTU/lb/°F | Medium: 24000 BTU / 36000 BTU |
| Large: 48000 BTU / 60000 BTU | ||
| Watts × 3.413 = BTU/HR | Gallons = cubic inches (in³) ÷ 231 | |
| Kcal/Hr × 3.968 = BTU/HR | Gallons = Liters × 0.2542 |