Portable Chillers Versus Central Chillers: Which is Best?

Heat Transfer

Portable Chillers Versus Central Chillers: Which is Best?

There are two types of chillers: portable chillers and central chillers.

Portable chillers are typically smaller in capacity (30-40 tons or less), simpler in overall design, and lower in installed cost.  Equipped with caster wheels, they are easy to move, easy to connect (using flexible hoses), and easy to power up.

Portable chillers are typically optimized to deliver a fixed amount of heat-transfer capacity, measured in tons. They are ideal when a piece of processing equipment needs a flow of cooling water at a significantly different temperature from other equipment.

They incorporate a single circuit, or zone, that handles heat transfer. They are well suited for use on processes where cooling requirements remain relatively constant.

As a rule, portable chillers operate most energy-efficiently when the cooling load closely matches the chiller’s rated capacity.*

Central chillers are generally larger in capacity, more complex in design, higher in energy efficiency, and higher in installed cost.

The key advantage of a central chiller system is that it can handle multiple, large and variable process loads that require cooling water of roughly the same temperature.

Central chillers incorporate features so that they can modulate their capacity to match changing production cooling needs:

·         separate process and circulating pumps
·         large cooling water reservoirs
·         multiple (or variable-speed) compressors
·         more sophisticated controls

One central cooler can generally provide better overall efficiency than multiple, portable chillers of the same total capacity.

 

* New portable chillers with optional variable-speed compressors, such as as the 10-ton and 20-ton EP2 Series from Conair can efficiently handle low, partial, and full chilling loads while providing dramatic power savings. In head-to-tests against 10- and 20-ton chillers equipped with conventional fixed-speed and digital-scroll compressors, EP2 Series portable chillers with variable-speed compressors delivered energy savings of 20-to 50% in a range of realistic conditions.

In order to choose between one central chiller or multiple portable chillers, the most important thing to know is the overall processing mix in your plant: As a rule, if 80% or more of a plant’s materials are processed within a ±5°F temperature range, a central chilling system will meet the need with less operating tonnage, floor space, and likely less daily maintenance than numerous portable units. 

 If, on the other hand, the materials processed have widely different temperature requirements, properly sized portable chillers may be more effective. In some cases, a mix of chillers—a central system designed to handle all but the lowest or highest temperatures, with portable chillers used for special or more extreme cooling needs—can be the best solution.

However, obtaining the substantial, long-term savings available by using a central chiller system requires a significantly greater up-front investment. A central chiller not only requires more complex controls, automation, and instrumentation in order to operate, but also a greater amount of dedicated plumbing to circulate coolant throughout the plant. Both types, however, require maintenance to keep the equipment healthy.

Clearly, there are many issues and factors to understand and consider before deciding on a heat transfer solution for a plastics processing plant. A competent and trusted equipment team member can help clarify and quantify plant requirements and also sort out subjective factors and intangibles that can drive a final decision.

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