In-house Sterling TT configurator

How to size a heat exchanger 

There’s no one-size-fits-all when it comes to reliable heat exchangers. To better understand this important aspect of heat exchanger design, we interviewed an expert from Sterling TT, Nic Zeoli, a seasoned mechanical engineer and Director of Engineering.

In this blog post, we’ll explore the insights shared by Nic, who sheds light on the intricate art of heat exchanger sizing.

Our heat exchanger expert

Nic Zeoli Director of Engineering at Sterling Thermal Technology
Nic Zeoli, Director of Engineering at Sterling TT

Nic boasts a rich background in heat transfer and fluid dynamics, making him a valuable asset to Sterling TT’s team. With a PhD in fluid dynamics from England and a passion for designing coolers, Nic has spent the last 13 years in the heat exchanger industry. He holds the prestigious title of a chartered engineer, a testament to his expertise in the field.


Factors influencing the design of heat exchangers

Nic explains that the design process starts with customers’ needs. They will have a required amount of heat to be exchanged between two fluids, and they will also specify any environmental constraints, such as size and weight. These requirements form the foundation of any new project.

Image of an FPSO in the ocean for which Sterling Thermal Technology delivers Avantair coolers
FPSO, a type of offshore facilities for which Sterling TT designed and manufactured generator coolers (Avantair)

However, achieving the optimal design is more than just fulfilling these requirements. Engineers must balance various factors, including cost, materials, and operational parameters, to find the perfect compromise.

For example, in an offshore facility, space is limited, and the heat exchanger probably needs to fit into a small area. There are also noise regulations to comply with. In this case, the trade-off might be a higher cost that fits the available space instead of  a cheaper unit made of less performing materials but with a larger envelope.

“Engineering, in general, is a trade-off. As soon as you join engineering sciences, you realise there is always compromises you must make. So, we try to find the optimum ones between the different factors that determine the size or the geometry of the cooler.”

For a different case, we could look at heat exchangers to be installed in a desert. The remote location means plenty of space for the heat exchanger to work, and high temperatures imply that a large surface area is required to dissipate the heat effectively. These heat exchangers are likely to be very large.

OFAF designed and manufactured by Sterling Thermal Technology
OFAF designed & manufactured by Sterling TT to keep a colossal power plant cool in desert conditions

Although the laws of heat transfer work the same for everyone, not all engineers will make the same decisions about how to compromise between the various factors. Nic stresses that this is where experience is crucial.

“What makes Sterling TT a successful manufacturer is that in our 100+ years of experience, we have also learned what doesn’t work. That means ensuring that something that works on paper also works in the first month, the second month, and for the next 15, 20, 25 years, and beyond.”

Specific applications

Sterling TT caters to diverse industries, from oil and gas to renewable energy to defence and chemical. Nic highlights some unique applications where the size of heat exchangers takes precedence.

Offshore applications – In offshore projects, space is at a premium, and noise regulations must be met due to personnel on board. Nic explains that striking a balance between minimising noise and size is particularly challenging.

Defence – Defence applications, such as propulsion motors on destroyers or submarines, need to be small, quiet and a special requirement is shock resistance. These heat exchangers must withstand potential explosions during wartime, which might add complexity to the mechanical design.

Remote locations – In remote areas where water is scarce, air-to-air heat exchangers play a crucial role in cooling electric motors. These units must dissipate heat when there are extremely high ambient temperatures, so a large heat exchanger is needed.

Large machines – In situations where the temperature difference between cooling and heating fluids is minimal, such as hot climate, enormous heat exchangers are required to handle large amounts of heat.

Servicing considerations – Heat exchangers have operating lives that are decades long, and during that time, they may need to be serviced or have parts replaced. A good design will include easy access to essential components.

Compliance with international design codes – Sterling TT ensures that its heat exchangers meet rigorous standards including but not limited to ABS, DNV, BV. The most recognised worldwide standard for pressure vessel is ASME VIII, and Sterling TT also complies with the ASME U stamp, indicating third-party inspection and certification. Additionally, they can design to various regional standards, such as EN, Australian, German, or French national standards, offering flexibility to clients globally.

Customisation is critical

Engineer working in the conceptual design department of Sterling Thermal Technology, sizing a heat exchanger
sizing a heat exchanger

Sterling TT takes pride in its bespoke approach to heat exchanger design. Unlike companies that rely on standard catalogue units, Sterling TT’s speciality lies in creating tailor-made solutions for each unique application.

“The important thing is that at Sterling TT, we don’t sell from a catalogue. We are experts at bespoke, special applications, such as when you are developing a new process or a new line. We’re the right partner for that.”

Sterling TT doesn’t sell off the shelf or only use predefined blocks. This allows us to address specific requirements and engineer a solution that works best for our customers, whether the heat exchanger is large or small.


Heat exchanger design is a complex art that requires engineers to balance multiple factors, including customer requirements, space limitations, noise regulations, and compliance with rigorous standards and cost competitiveness. Sterling TT’s bespoke approach, coupled with its rich experience and expertise, allows us to create custom heat exchange solutions that meet each client’s unique needs and applications. As Nic aptly puts it, “Experience is what makes the difference,” which is why Sterling TT is a trusted partner in the world of heat exchanger design and manufacture.

If you need a bespoke heat exchanger, contact us

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