5 Sizing Steps for Chillers in Plastic Process Cooling

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:

  1. The incoming water temperature
  2. The chilled water temperature required
  3. 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 25-Ton) chiller is required

 

A 20 ton cooling-capacity chiller from Cold Shot Coolers

A 20 ton cooling-capacity chiller from Cold Shot Coolers

 

Plastic Process Cooling Applications

There also industry-specific, rules-of-thumb 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 3-ton 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 water-cooled chillers and air-cooled 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.