How do I work out the cooling capacity that I need?

Where possible, check the technical documentation for the equipment or process you need to cool.

The manufacturer may provide a:

• Heat load or heat rejection figure
• Cooling capacity requirement
• Maximum thermal load
• Required coolant flow
• Required inlet temperature
• Pressure requirement

If a cooling requirement is already specified by the equipment manufacturer, this is normally the best starting point.

Make sure that the figure refers to the thermal load that needs to be removed, rather than simply assuming that an electrical power rating represents the required cooling capacity.

Where no thermal-load information is available, the electrical power consumed by the unit can sometimes be used to estimate its maximum heat output.

As a conservative starting point, you can assume that the electrical power consumed by the equipment is ultimately converted into heat.

For example, if equipment consumes 1,000W, its heat load could be estimated as up to approximately 1kW before any appropriate design allowance is considered.

However, this method may overestimate or underestimate the actual process heat load depending on how the equipment operates and where its energy is dissipated.

If you are unsure whether an electrical rating can be used in this way, provide the equipment details to ATC and we can help assess the requirement.

If you have an existing cooling circuit and know the coolant flow rate and the temperature difference between the fluid entering and leaving the application, these can be used to estimate the heat being transferred to the coolant.

The calculation is based on:

Heat load = mass flow x specific heat capacity x temperature difference

To calculate this accurately, you need to know:

• Heat transfer fluid being used
• Fluid flow rate
• Fluid temperature entering the application
• Fluid temperature leaving the application
• Density of the fluid
• Specific heat capacity of the fluid

This method can be particularly useful when replacing an existing chiller or assessing an operating process.

Remember that the thermal properties of a glycol-based heat transfer fluid differ from those of water, so the correct fluid properties should be used in the calculation.

Some applications need to remove heat continuously, while others also have a pull-down requirement – for example, cooling a known volume of fluid from one temperature to another within a specified period.

In this case, the cooling requirements can be estimated using:

• Mass or volume being cooled
• Starting temperature
• Required final temperature
• Required cooling time
• Specific heat capacity of the material or fluid

Any heat being continuously generated by the application during the pull-down period also needs to be considered.

Tell ATC if your process has a specific cool-down time requirement so that this can be considered during chiller selection.

Some allowance may be appropriate where the heat load is estimated or where operating conditions can vary.

However, simply selecting the largest possible chiller is not necessarily the best approach.

The appropriate design allowance depends on how accurately the heat load is known, how much the process varies and the operating conditions of the application.

ATC can help assess an appropriate cooling requirement where there is uncertainty.

A chiller’s cooling capacity is not necessarily constant across its operating temperature range.

The cooling capacity available can change with both the required process fluid temperature and the ambient conditions surrounding the chiller.

For example, a chiller described by a nominal kW capacity at one operating point may provide a different cooling capacity when operating at a lower process temperature or higher ambient temperature.

This is why ATC provides model-specific cooling curves and technical performance data.

See “Why does cooling capacity change with temperature?” for more information.

Ambient temperature can affect the ability of an air-cooled chiller to reject heat.

Higher ambient temperatures can reduce the cooling capacity available from the refrigeration system, so the expected environment needs to be considered when selecting a chiller.

Always provide ATC with the maximum expected ambient temperature around the chiller, rather than only the general room temperature.

See “How does ambient temperature affect chiller performance?“ for further guidance.

Cooling capacity is one of the most important selection criteria, but it is not the only one.

To specify an appropriate chiller, ATC will also consider:

• Required process fluid temperature
• Coolant flow and pressure requirements
• Heat transfer fluid
• Maximum ambient temperature
• Electrical supply
• Application and installation environment
• Temperature stability requirements
• Any specific configuration or accessory requirements

These factors need to be considered together to ensure that the selected chiller is suitable for the application.

You do not need to calculate everything yourself before contacting ATC.

If the heat load is unknown, provide as much information about the application as possible, including manufacturer and model details for the equipment being cooled, electrical power information, existing cooling arrangements, operating temperatures, and any available flow data.

Our team can review the information and help establish the cooling requirement.

For existing systems, measurements such as coolant flow and inlet/outlet temperatures may also help us to estimate the actual process heat load.

Contact ATC with your application details and our team can help determine the cooling capacity required and identify an appropriate chiller.