Abstract: Heat is indirectly transferred between a process fluid and ambient air in apparatus that includes an evaporative heat transfer cell operative in a wet mode or a dry mode, a dry heat transfer cell and a fan. The air may bypass the dry heat transfer cell to flow through a first air passage or may flow through a second air passage through the dry heat transfer cell and in either event, then through the evaporative heat transfer cell. The air may partially flow through and partially bypass the dry heat transfer cell, and then through the evaporative heat transfer cell. The evaporative heat transfer cell optionally may include a direct contact evaporative heat exchanger.

Abstract: A hybrid heat exchange apparatus for indirectly transferring heat between a process fluid and ambient air includes an evaporative heat transfer cell operative in a wet mode or a dry mode, a dry heat transfer cell and a fan. The air may bypass the dry heat transfer cell to flow through a first air passage or may flow through a second air passage through the dry heat transfer cell and in either event, then through the evaporative heat transfer cell. The air may partially flow through and partially bypass the dry heat transfer cell, and then through the evaporative heat transfer cell. The evaporative heat transfer cell optionally may include a direct contact evaporative heat exchanger. Manually or automatically controlling air flow based on ambient conditions provides efficient and economical control of the hybrid heat exchange apparatus, while avoiding problems in freezing conditions.