Chillers enable heat removal for a wide range of equipment and processes. To get the most efficient process, it is important to understand the proper sizing and specification required for each application. Installing the right chiller can increase production speed and accuracy, protect valuable process equipment against damage, and reduce water consumption and related costs. An undersized chiller can result in inadequate chilling of the items and if the chiller is too large it will be inefficient due to excessive cycling.
In addition to having an adequate cooling capacity, the chiller must deliver the cooling fluid at the proper pressure and flow rate.
Factors Impacting Chiller Size
There are four basic factors impacting chiller sizing and selection:
Desired Coolant Temperature
This is the coolant temperature at the process or equipment inlet. At this point one needs to measure the temperature to enable the coolant heating as it travels from the chiller to the process. The potential heat gain is more when the distance to be covered is longer. This heat gain can be reduced by insulation of the cooling line and positioning the chiller as close as is practical to the equipment or process being cooled.
Heat Load
This is defined as the amount of heat that must be removed and is normally expressed in BTUs/hour or watts. The heat load value is normally provided by the equipment manufacturer. Otherwise it can be calculated with the following formula:
Heat load = Flow rate x Fluid density x Fluid specific heat x Constant x ΔT°
This is shown in Table 1
Table 1. Units and Calculations for heat load
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Image credit: PolyScience
Coolant Flow and Pressure
Coolant flow and pressure are normally provided by the equipment manufacturer and are a function of the surface area and the heat transfer characteristics of the process/material being cooled. It is critical that the chiller delivers the coolant at the right pressure and flow rate. In case the pressure or flow rate is very high, the cooled equipment may be damaged. In case it is too low, the heat removal will not be enough. PolyScience can help in specifying the size and type of coolant pump most suitable for one’s needs.
Condenser Heat Dissipation
The final factor influencing chiller/heat exchanger selection is how the heat removed will be dissipated. Chillers with air-cooled condensers exhaust heat into the surrounding air and require only power and ventilation for operation. Chillers with water-cooled condensers transfer heat to the facility's cooling water supply. There are naturally other factors such as heating capability, external temperature tracking and de-ionized water capability that impact the ultimate configuration of a chiller. PolyScience can take all these into consideration while helping in selecting the right chiller.
Data Required for Chiller Selection
The data required for selecting the best chiller is:
- Desired coolant temperature at the inlet to one’s process or equipment
- Anticipated heat load as determined or specified by the equipment manufacturer
- Cooling fluid flow rate and pressure requirements
- Maximum room or ambient temperature where the chiller will be located
- Internal heat dissipation, space, and portability needs
- Special requirements such as remote temperature tracking or piping for de-ionized water
It is normally recommended that 20% to 50% be added to the calculated heat load to provide a safety factor if the chiller will be operated at ambient temperatures above 20°C (68°F), at high altitude or if the heat output of the device is variable. This also offers a margin of safety for future cooling needs.
Suggested Chiller Fluid
The most popularly used and acceptable coolant is a mixture of 50% distilled water and 50% glycol (polycool EG-25). This combination will provide the best results for set-point temperatures between -25°C and +80°C (-13°F and +176°F). Even though ethylene glycol is not required for set-point temperatures above freezing (0°F/+32°F), it is highly recommended as glycol helps lubricate pump seals and fluid temperatures inside the chiller may be below freezing.
Cooling capacity curves for different chillers are shown in Figure 1.
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Figure 1. Cooling capacity curves are representative of the model shown and may vary depending on pump type, heat load, and ambient conditions. Image credit: PolyScience
This information has been sourced, reviewed and adapted from materials provided by PolyScience.
For more information on this source, please visit PolyScience.