# Airflow Networks Definitions

| **Term**                         | **Definition**                                                                                                                                              | **Units**    |
| -------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------ |
| **Airflow Network Model**        | A simulation method in EnergyPlus that calculates the airflow through building components and zones based on pressure differences.                          | -            |
| **Node**                         | A point in the airflow network where air properties like temperature, pressure, and humidity are defined.                                                   | -            |
| **Linkage**                      | A connection between two nodes that represents a pathway for airflow, such as through a door, window, or duct.                                              | -            |
| **Zone**                         | A space or collection of spaces within a building with uniform air properties used in airflow calculations.                                                 | -            |
| **Surface**                      | The physical boundary in a building, such as walls, floors, ceilings, and roofs, that interact with airflow.                                                | -            |
| **Pressure Coefficient (Cp)**    | A dimensionless number that characterizes the effect of wind pressure on building surfaces.                                                                 | -            |
| **Crack**                        | A small opening in the building envelope that allows uncontrolled air leakage, typically due to construction imperfections.                                 | -            |
| **Opening**                      | A controllable opening like windows, vents, or doors that can be adjusted to regulate airflow.                                                              | -            |
| **Infiltration**                 | Uncontrolled air leakage into a building through cracks, gaps, or openings in the building envelope.                                                        | m³/s         |
| **Ventilation**                  | Controlled air exchange between the building and the external environment, which can be natural or mechanical.                                              | m³/s         |
| **Exfiltration**                 | Uncontrolled air leakage out of a building through cracks, gaps, or openings in the building envelope.                                                      | m³/s         |
| **Mechanical Ventilation**       | The use of mechanical systems, such as fans and ducts, to supply, distribute, and exhaust air within a building.                                            | m³/s         |
| **Natural Ventilation**          | The process of supplying and removing air through natural forces like wind pressure and thermal buoyancy, without mechanical assistance.                    | m³/s         |
| **Airflow Path**                 | The route taken by air as it moves through the airflow network, including through openings, ducts, and around obstacles.                                    | -            |
| **Local Wind Pressure**          | The wind pressure exerted on specific building surfaces, which varies with wind speed, direction, and building geometry.                                    | Pa (Pascals) |
| **Air Distribution System**      | The network of ducts, vents, and registers that distributes conditioned air (heated, cooled, or ventilated) throughout the building.                        | -            |
| **Stack Effect**                 | The movement of air into and out of buildings due to temperature differences between the indoor and outdoor environment, creating pressure differences.     | Pa (Pascals) |
| **Wind-Driven Ventilation**      | Natural ventilation driven by wind forces, where the wind creates pressure differences across the building envelope, promoting airflow.                     | m³/s         |
| **Buoyancy-Driven Ventilation**  | Natural ventilation driven by buoyancy forces, where warmer air rises and cooler air enters the building to replace it, creating airflow.                   | m³/s         |
| **Duct Leakage**                 | Air leakage from ducts in the air distribution system, which can lead to energy losses and reduced system efficiency.                                       | m³/s         |
| **Effective Leakage Area (ELA)** | A measure of the total area of all leaks in a building envelope, standardized to a reference pressure difference, indicating the tightness of the building. |              |