Why Ambient Temperature Matters in Air-Cooled Heat Exchanger Design

Air-cooled heat exchangers use the surrounding air to remove heat from a process liquid or gas. That makes the temperature of the available air one of the most important conditions in the design.

An exchanger selected around a convenient average temperature may not deliver the required duty during the hottest operating periods. For dependable cooling, the design needs to account for the most demanding ambient temperature at which the specified outlet condition must be achieved.

Why the design ambient temperature matters

Heat transfer depends partly on the temperature difference between the process fluid and the cooling air. As the ambient air temperature rises, that difference becomes smaller and the cooling duty becomes more demanding.

This is particularly important for equipment operating in hot or dry locations, where cooling water may be limited and air cooling is selected as the practical solution. If the unit is required to maintain a defined process outlet temperature, the thermal design must reflect the expected site conditions.

Spiro-Gills designs each air-cooled heat exchanger around the required duty and the worst potential ambient temperature supplied for the project. The objective is to provide the correct outlet temperature under the stated design conditions.

More than a single temperature figure

The ambient design point forms part of a wider set of project requirements. The thermal engineers also need to understand the process fluid, inlet and outlet temperatures, flow rate, operating pressure and applicable design requirements.

Together, this information determines the heat that must be removed and the heat-transfer surface required. It also influences the configuration of the complete cooler, including the finned-tube bundle and airflow arrangement.

The result is an air cooler engineered for a defined application rather than selected as a generic item of equipment.

Designing for different operating environments

Industrial air coolers may be installed in very different climates. Spiro-Gills equipment operates in locations ranging from Arctic conditions to equatorial environments, supporting applications in oil and gas, power generation, process cooling, refineries and chemical works.

The operating environment can influence material selection and the overall construction of the unit. Spiro-Gills selects from its range of finned-tube systems to suit the application and provide a cost-effective heat-transfer surface.

Forced and induced draft arrangements

Air-cooled heat exchangers are commonly arranged as forced or induced draft units.

• Forced draft: fans push air from beneath the tube bundle and discharge it through the top of the cooler.
• Induced draft: fans draw air through the tube bundle before discharging it from the top of the unit.

Each arrangement has different characteristics. The appropriate choice depends on the operating duty, temperature-control requirements, environment and project priorities. It should therefore be considered as part of the complete thermal and mechanical design.

Built around the required duty

Spiro-Gills has designed and manufactured fin-fan air-cooled heat exchangers in the UK for more than 70 years. Its Stafford facility can manufacture the major elements of the exchanger under one roof, including finned-tube bundles and the supporting air-cooler structure.

Every product is manufactured and tested on site before delivery. This combines thermal engineering, manufacturing and testing within a single UK facility.

If you are specifying a new or replacement air-cooled heat exchanger, provide the Spiro-Gills team with the process duty, design conditions and available project information. We can review the requirement and discuss an engineered solution for the application.

Contact Spiro-Gills about your air-cooled heat exchanger requirement.