Using the sun, wind, and surrounding site features such as the earth, these buildings are designed so well that they minimize energy use for heating, cooling, and ventilation. Heat loss in the cold winter months and heat gain from the summer sun are of high importance for these buildings. It is often difficult to determine the impact that certain design elements will have on yearly energy use. A whole-building simulation program such as EnergyPlus can help to predict energy use as well as determine how to best implement design features. The Sketchup image below show some of the important considerations in the design of a passive building design:
Free-running temperature analysis in a passive home:
Passive buildings are designed to use little, if any, energy for heating and cooling. Internal gains from people, lights, cooking, and plug loads are oftentimes adequate to provide enough heat for meeting the indoor heating setpoint. Ground contact and natural ventilation often meet much of the cooling load, while proper window overhangs limit the addition of heat. For designers of these buildings, it is very useful to see the hourly temperatures at certain times of the year within the home without a heating or cooling system. This ‘free run’ approach can be effectively accomplished with EnergyPlus. The first figure below shows a well insulated home with R28 SIP walls and an R42 SIP roof. It also has been modeled with adequate slab insulation and a low air infiltration rate. The second figure shows more south-facing windows, all other construction elements kept the same. Several south-facing skylights are added to the third figure.
Graphs of this free-running temperature for short winter and summer periods are shown below.