In some situations it is important to know the effect of bulk air flow from one room to another and through the whole building that may be driven by wind and buoyancy effects. Inter-zone airflow models and tools are used to calculate the air pressures and buoyancy forces in order to quantify such air flows and how they vary over time. This also allows the flow of contaminants such as carbon dioxide and even smoke to be simulated. Such simulation methods can be used in conjunction with energy simulation tools (see 2.2) to estimate the combined effects of building heat transfer and bulk air flow throughout the year.