Dry coolers are used in many air cooled refrigeration systems. In case of low outdoor temperatures, outdoor air can be applied for cooling applications. In dry coolers, large fans create a forced airflow along air-to-water heat exchangers. Subsequently, the water circuit can be used for cooling of data centers, office buildings and industrial processes.
For a guaranteed cooling capacity of the dry coolers, the temperature of the forced airflow must be as low as possible. It is often assumed that the air temperature at the inlet of the dry cooler corresponds to the free field outdoor temperature. User manuals of dry cooler systems give only rough guidelines to achieve this:
- A sufficient free area at the air inlet, where the free space around the dry cooler must be at least 1 meter.
- The exhaust air side must be free of obstructions.
- No short-circuits in the air circulation.
Practical experience has shown that following the first two guidelines is not sufficient. The question is how the third guideline can be guaranteed. Apart from temperature measurements and smoke tests afterwards, Computational Fluid Dynamics (CFD) can be used to analyse the performance of dry cooler systems.
Practical advice is avoid locating dry coolers behind walls where airflow can be diverted from the output back into the input airflow. Even where the first two installation rules are followed, temperature increases of up to 1.7 °C have been observed when units are installed adjacent to walls or other airflow obstructions.