As the previous chapter demonstrated, if a building is properly designed, natural ventilation can provide both a comfortable and healthy indoor environment as well as energy savings. Most architects and designers know about the principles of passive solar heating and can indicate how they desire small buildings to also take advantage of natural ventilation, as shown in Figure 1. Natural ventilation and thermal comfort, however, are difficult to understand and model, even for simple buildings. It is important that the architects and engineers collaborate early in the design process when key decisions about master planning and building geometry are made.