For residential buildings, the thermal envelope components are typically designed as standard -satisfied. However,
from the life-cycle viewpoint, the thermal performance during the installation, maintenance and operation phases
will usually differ from during the design phase. The main reasons include the installation deviation, thermal bridge,
and the insulation aging, etc. A home energy audit can help home owners determine where their houses is losing
energy and money, and how much problem can be corrected to make their home more energy efficient. Traditional
energy audit, also called on-site energy audit, is usually conducted by a trained energy engineer physically walking
through the building to determine energy consuming characteristics and opportunities. A detailed traditional energy
audit often involve advanced on-site measurements and computer-based simulation tools to calculate a more accurate
energy cost for one year, and create a report of the anticipated energy performance of the building. Over the last few
years, virtual energy audit has been increasingly used to find out whether or not a building is operating efficiently.
Unlike traditional energy audit, virtual energy audit requires no contact with the building itself or its owner. It
collects meter data, weather information, information about similar buildings, and other publicly available
information and analysis them through algorithms.