Which of the following is essential for a building's energy efficiency?

A proper ventilation system is essential for a building's energy efficiency because it directly affects the management of indoor air quality and temperature. Efficient ventilation helps to reduce the need for excessive heating or cooling by maintaining a comfortable indoor environment. It also minimizes energy loss and waste by ensuring that fresh air enters the building while stale air is expelled, preventing the overworking of heating and cooling systems.

In contrast to ventilation systems, options such as brightly colored exteriors, a large number of windows, and high ceilings may not contribute effectively to energy efficiency. While they can have aesthetic value or potentially affect natural lighting, they do not play a crucial role in regulating temperature and air quality within the building. This highlights the importance of mechanical and thermal systems, like ventilation, in achieving energy efficiency.