Revolving doors are much more energy efficient than conventional doors. This is because they let less air out of the building than a regular door. They let out 75% less air per person.
How does this translate in to energy savings? Most big buildings like libraries, office buildings, and others that utilize these doors condition their air. In other words these buildings heat or cool their air for the comfort of their occupants and for the operation of certain machines. It takes energy to change and condition the air in this manner so every time air is lost to the outside new air has to be heated or cooled to match the rest of the building. This means that the more air lost each time someone passes through the door the more energy it takes to fix that.
Something so small adds up in a building as so many people pass through its doors. So do your part use the revolving doors at the school library or anywhere else you come across them. It'll help save the planet one step at a time.