As efforts toward energy efficiency and decarbonization accelerate, many factories and data centers that rely on cooling processes are facing challenges related to aging chillers and rising operating costs. Even facilities where equipment renewal was once considered a long-term issue may now require reassessment from the perspectives of energy efficiency, lifecycle cost, and operational reliability. A chiller is not merely a cooling device. It is a critical infrastructure component that directly affects production quality, operational stability, and a company’s overall energy costs. For this reason, the choice of cooling method during equipment renewal can have a significant impact on future operating costs and the success of long-term decarbonization strategies. The two most common cooling methods are air-cooled chillers and water-cooled chillers. While both systems transfer heat using refrigerant, their heat rejection methods and system configurations differ, resulting in different suitability depending on application and operating conditions. Understanding the characteristics of both air-cooled and water-cooled systems is essential—not simply for comparison, but for accurately defining cooling requirements before system design begins. This article outlines the key characteristics of each system and provides guidance on how to evaluate cooling requirements, while also introducing how Mitsubishi Heavy Industries Thermal Systems (MTH) approaches cooling system engineering.

An air-cooled chiller rejects heat directly to the ambient air. Because it does not require cooling towers or cooling water pumps, it is typically installed outdoors.

Its relatively simple structure and minimal piping requirements allow for flexible installation, making it well suited for replacement projects or capacity expansion.

Air-cooled chillers are commonly adopted in facilities where securing cooling water is difficult or where cooling tower installation is constrained. Their compact footprint and short construction period also make them ideal for retrofit projects and installation in existing buildings.

Because air-cooled chillers are installed outdoors, their performance and durability are more susceptible to ambient conditions such as temperature, humidity, wind, dust, and rainfall. To ensure stable long-term operation, the following considerations are essential:

A water-cooled chiller (Especially Centrifugal Type) rejects heat via cooling water. The system includes a cooling tower, pumps, piping, and water treatment equipment. Water-cooled chillers are available in several compressor types, including screw, scroll, and centrifugal (turbo). Among these, centrifugal chillers, which MTH primarily offers, are widely adopted in large facilities due to their high efficiency and suitability for large-capacity operation. They are commonly used in industrial plants, large commercial buildings, and data centers where stable, continuous cooling is required.

Compared to air-cooled systems, water-cooled chillers involve more auxiliary equipment, including cooling towers, pumps, piping, and water treatment systems. Adequate installation space and a well-planned maintenance framework are therefore essential. In addition, insufficient water quality management may lead to scaling or corrosion, which can degrade performance and shorten equipment life. A structured maintenance and water treatment plan is indispensable to sustain system performance.

There is no single “correct” answer when selecting a chiller. What matters most is defining cooling requirements based on site-specific conditions.

Mitsubishi Heavy Industries Thermal Systems (MTH) offers both air-cooled and water-cooled chiller solutions in Japan, while overseas it maintains a framework to design and propose optimal cooling systems based on application requirements, system scale, and local environmental conditions. By analyzing operating data, load characteristics, and future operational plans, MTH supports customers in translating cooling needs into optimized system designs. Consultation typically starts with understanding cooling loads, operating patterns, and long-term energy objectives—before discussing specific equipment. The optimal chiller system is not simply selected—it is designed. MTH works with customers as an engineering partner, supporting cooling system design that balances efficiency, decarbonization, and long-term operational reliability.