i Recommissioning: optimizing the performance and operation of an existing building’s system. Following investigation, the measures implemented can include equipment maintenance, adjustments to controls, and minor equipment retrofits. This includes things like upgrading lighting, improving indoor air quality and replacing boilers.
ii Deep retrofits involve major system and equipment replacement or upgrade. Typically pursued during building renewal events such as envelope and major equipment replacement, new ownership or occupancy, and green building certification. It can include HVAC changes, window replacement, and other envelope and system upgrades.
iii Renewable energy: while many forms of on-site renewable energy exist, including solar thermal, biomass, wind and micro-hydro, solar photovoltaic (PV) electricity generation is most commonly used in existing buildings.
iv Fuel switching actions: switching natural gas and other carbon-intensive heating furnaces, boilers and distributed equipment to low carbon sources like high-efficiency electricity-based systems such as heat pumps.