An energy model predicts how much energy a building will use based on insulation, windows, configuration, size, orientation and many more inputs.  Models are required for many certifications.  To reach Net Zero Energy multiple models are used and coordinated.   These are described below.

The WuFi energy model is a very detailed accounting of all construction components and strategies from the insulation values to how the windows are installed to the spacers between the window glass.  Because it is rich in detail, it can be very accurate at predicting actual use.

Energy Star requires a specific model that produces a Home Energy Rating (HERS) Score.  This model compares a code built home (scored at 100) to a energy efficient home.  If the efficient home is modeled to use 15% less energy than the code built home, it has a HERS 85. 

A net zero energy home has a HERS score of 0. 

Heating and cooling systems have it's own model (a Manual J) that predicts the amount of heating & cooling energy needed for the home.  A detailed Manual J is essential to size equipment and ducts properly.