A dry bulb switchover temperature refers to the temperature at which a closed circuit cooler can run fully dry (with just the fans running, without the spray pumps on) and reject 100% of the design heat load. This is an important term in the engineering community as a higher dry bulb switchover temperature results in reduced water consumption throughout the year.
Since the process fluid is contained within a steel coil, when ambient conditions are colder than the dry bulb switchover temperature, closed circuit coolers can utilize airflow over the coil to achieve the required heat rejection with just the fans operating.
When a fluid cooler is sized for a dry bulb switchover temperature, this means that the pumps are off and the fans are running at 100%.
Hybrid coolers utilizing coils with extended surface fins can achieve much higher dry bulb switchover temperatures due to the additional surface area on the coil.
EVAPCO eco-coolers utilize finned coil technology and can achieve dry bulb switchover temperatures for full load (95/85/78 degrees F design conditions) up to 45 degrees F. EVAPCO eco-Hybrid coolers can achieve dry bulb switchover temperatures for full load (95/85/78 degrees F design conditions) up to 65 degrees F.