A 1999 study by Detlef Westphalen andScott Koszalinski, Energy Consumption Characteristics of Commercial Building HVAC Systems looked at parasitic energy consumption. Following are some excerpts from this study. If you own or maintain buildings, this is well worth reading.
Parasitic energy use, the energy used to power the fans and pumps which transfer heating and cooling from central heating and cooling plants to conditioned spaces, can represent a significant portion of this energy (from 20% to 60% of HVAC electricity use in a building).
Parasitic energy use in commercial building HVAC systems accounts for about 1.5 quads of primary energy use annually, about 10% of commercial sector energy use.”
Supply fans use so much energy (about 0.75 quad total) because
(1) they are used in virtually 100% of system types as defined (note that the evaporator fans of packaged or individual systems as well as fan-coil unit fans are considered in this category),
(2) air is an inherently inefficient heat transfer medium,
(3) typical air distribution design practice involves considerable pressure drop for filtration, cooling and heating coils, terminal boxes, and diffusers, and
(4) many of these fans operate at 100% power during all building occupied periods.
Operations and maintenance plays a critical role in managing parasitic energy. Ensure supply fans are operated only as needed, air filters, coils, and dampers are clean and maintained, and operate fans at the lowest acceptable speed. See my blog on the energy cost of air filters.