Sizing a chiller for your molding shop is important for the following reasons:
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If too small a chiller is selected, the undersized unit will never cool the
processing equipment - creating bad parts.
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Choosing too large a chiller, can allow for future expansion.
However, the company could be paying for capacity that will never be used.
Because of these issues, sizing a chiller to slightly exceed the capacity
requirements is the most cost effective option. To facilitate this
choice, we recommend the following calculations for providing data to the
decision-making process. In addition, utilizing more than one formula to
"cross-check" operations is recommended.
Concepts and Definitions
The first law of thermodynamics says that the total quantity of energy in the
universe remains constant. This is the principle of the conservation of energy.
HEAT IN = HEAT OUT
The HEAT IN part of the equation can come from a variety of sources, most
commonly:
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Cartridge heaters
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Heater bands
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Circulators/hot water
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Plastic melt stream
The HEAT OUT part of the equation is primarily a chiller. Some heat is
lost by natural conditions such as being emitted into the ambient air.
Systems where it is not desirable to lose heat (energy) to the surrounding air
use some form of insulation.
For the purposes of this illustration, the universe can be defined simply
as a Plastic Processing Apparatus that has some form of heat source and is
being cooled by an IMS Chiller. Here is a simple schematic:
The arrow shows flow of the heat transfer fluid which is typically a mixture of
ethylene glycol
and water. Optimum heat transfer is commonly 25% glycol by volume.
Propylene glycol can also be used.
The Plastic Processing Apparatus can be any number of physical items.
Some of the most common are:
-
an injection mold
-
an extrusion die
-
an extrusion cooling tank
To accurately size the chiller using the above definitions and principles, you
can see that it is necessary to define (and ideally measure) all sources of
heat going IN or OUT of the process. With this understanding, we can now
discuss some common ways to approach chiller sizing.
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