No matter what your application, there is a single formula for determining the size of chiller you need. Before you begin, you must know three variables:
 The incoming water temperature
 The chilled water temperature required
 The flow rate
For our example, we will calculate what size chiller is required to cool 40 GPM (gallons per minute) from 70 °F to 58 °F? Use the following five steps and general sizing formula:
1. Calculate Temperature Differential (ΔT°F)
ΔT°F = Incoming Water Temperature (°F)  Required Chilled Water Temperature.
 Example: ΔT°F = 70°F  58°F = 12°F
2. Calculate BTU/hr.
BTU/hr. = Gallons per hr x 8.33 x ΔT°F
 Example: 40 gpm x 60 x 8.33 x 12°F = 239,904 BTU/hr.
3. Calculate tons of cooling capacity
Tons = BTU/hr. ÷ 12,000
 Example: Ton capacity = 239,904 BTU/hr. ÷ 12,000 = 19.992 tons
4. Oversize the chiller by 20%
Ideal Size in Tons = Tons x 1.2
 Example: 19.992 x 1.2 = 23.9904
5. You have the ideal size for your needs
 Example: a 23.9904 (or 25Ton) chiller is required
A 20 ton coolingcapacity chiller from Cold Shot Coolers
Plastic Process Cooling Applications
There also industryspecific, rulesofthumb for chiller sizing. These may vary depending upon the application. The below guidelines and formula may be used for sizing chillers for plastic process cooling applications. In our example, we will calculate what size chiller is needed for a polypropylene molding operation that incorporates a 6oz. "Shot Size" and a 18 second cycle time with a 3 H.P. hydraulic motor. We will use Charts 1 and 2 as references.
1. Calculate the pounds of material per hour being processed.
 Example: 6 oz. / 18 sec. = 19.99 oz/min (20.00 oz./min)
 20 oz. / min x 60 min. = 1200 oz/hr
 1200/16 = 75 lbs. / hr
2. Determine how many pounds per hour are required for each ton of cooling capacity using Chart 1.
 Example: Polypropylene requires 1 ton of cooling capacity for every 35 lbs./hr processed
 75 lbs. ÷ 35 lbs. = 2.14 tons of cooling
3. Determine if the extruder or any auxiliary equipment will require chilled water using Chart 2. If not, go to step #5.
 Example: A hydraulic motor requires 0.1 ton/HP of cooling capacity
 3 HP x 0.1 ton/HP = 0.3 ton of capacity
4. Combine the process and auxiliary equipment cooling requirements.
 Example: 2.14 tons + 0.3 ton = 2.44 tons
5. Size your chiller by rounding up to the closest standard unit.
 Example: This application will require a 3ton unit
Chart 1: Plastic Material Process Cooling Requirements
Injection Molding 
30#/hr H.D. Polyethylene 
1 ton 

35#/hr L.D. Polyethylene/Polypropylene 
1 ton 

40#/hr Nylon 
1 ton 

50#/hr Polystyrene or ABS 
1 ton 

65#/hr PVC or Polycarbonate 
1 ton 

70#/hr P.E.T 
1 ton 
Extrusion 



50#/hr Polyethylene/Polypropylene 
1 ton 

75#/hr Polystyrene 
1 ton 

80 #/hr PVC 
1 ton 
Blow Molding 
35#/hr Polyolefins 
1 ton 
Source: www.waterchillers.com
Chart 2: Auxiliary Equipment and Extruder Cooling Requirements
Extruder Cooling 
Gear box cooling 
1 ton/100 hp 

Feed throat: 3” screw or less 
1 ton 

Feed throat: larger than 3” screw 
2 ton 

Barrel or screw cooling (per inch of screw diameter) 
1 ton/inch 
Auxiliary Equipment Cooling 



Air compressor (no aftercooler) 
0.16 ton/hp 

Air compressor (with aftercooler) 
0.2 ton/hp 

Vacuum pump 
0.1 ton/hp 

Hydraulic cooling 
0.1 ton/hp 

Hot runner mold 
0.1 ton/hp 

Water pump in circuit 
0.1 ton/hp 

Feed throat: less than 400 ton 
0.5 ton 

Feed throat: greater than 400 ton 
1 ton 
Source: www.waterchillers.com
About Cold Shot Chillers®
Based in Houston, Texas, Cold Shot Chillers® manufactures economical, ruggedly dependable industrial air cooled chillers, water cooled chillers, portable chillers and central chillers. Our industrial watercooled chillers and aircooled chillers serve a variety of different industries and applications.
Cold Shot Chillers® began in the late 1970s as an HVAC repair company in Houston, Texas. In 1980, the company began manufacturing new chillers for the plastic process industry and refurbishing used chillers for an assortment of industries. As our new chiller sales grew the company emphasis shifted from service to 100% manufacturing. Primary industries served include plastic processing, food & beverage, and metal finishing.
For more information contact Bob Casto, Business Development Manager, Cold Shot Chillers®.
To read more articles about Chiller Technology, visit www.coolingbestpractices.com/technology/chillers.