Which component directly reduces a building's Greenhouse Gas (GHG) emissions?

A high-efficiency HVAC (Heating, Ventilation, and Air Conditioning) system can directly reduce a building’s greenhouse gas emissions by using less energy than a standard system. Since most energy production involves the burning of fossil fuels, which releases greenhouse gases, using less energy results in fewer emissions. References: LEED Green Associate Candidate Handbook, U.S. Green Building Council resources