Set of 3 booklets – GN11/97 Oversized air handling plant; GN12/97 Oversized heating plant and GN13/97 Oversized cooling and pumping plant. It is estimated that this oversizing is typically responsible for approximately 10- 15% of HVAC-related energy consumption. These booklets present a four- step methodology for reducing the energy consumption of oversized plant - 1) targeting oversizing, 2) assessing and optimising operation and maintenance practice, 3) accurately quantifying overcapacity by plant monitoring, 4) implementing remedial measures.