Supply air temperature Reset is a control strategy to help minimize VAV reheat. The supply air design temperature (typically 55 degrees Fahrenheit) is raised as high as 60, or 65 degrees or until at least one of the VAV boxes on the system is 100% open. This often occurs during morning and evening hours when the cooling load is low or near zero. It also occurs in "swing months", such as the spring or fall.
Example:
The purpose of of Supply air temperature reset is to save on reheat energy. It should be noted that it will increase fan energy, and may not be beneficial where humidity control is needed