How does energy efficiency in buildings reduce energy demand?

• A. Only reduces water usage.
• B. Increases energy use.
• C. No effect on energy demand.
• D. Insulation reduces heat loss, high-efficiency heating/cooling reduces energy use, and efficient lighting reduces electricity consumption.

Answer: (D)

Energy demand in buildings is lowered when we reduce the amount of energy needed to heat, cool, and light the interior. Insulation and sealing slow heat transfer through walls, roofs, and gaps, so the indoor temperature stays comfortable with less heating in winter and less cooling in summer. High‑efficiency heating and cooling systems use less energy to achieve the same indoor climate. Efficient lighting, especially using LEDs, uses far less electricity for the same amount of light. Put together, these measures cut the overall energy required to operate a building. The other options miss the fact that improving insulation, better heating/cooling efficiency, and efficient lighting directly reduce energy use, not water usage, not energy consumption, and not have no effect.