Airflow Networks
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An Airflow Network model enables detailed simulation of multizone airflows, incorporating both natural and forced air distribution systems, while accounting for heat and moisture exchanges within a theoretical air distribution network.
Airflow Networks are only available in .
Essential information for airflow calculations, such as zone volumes, neutral heights, the orientation and location of building surfaces with openings, is automatically extracted from the building description used for thermal modeling. This includes infiltration specification on cracks or openings through which air can flow.
Using this information, a "pressure-flow network" is constructed that is solved iteratively at each timestep in a simulation to determine unknown pressures and air flows based on numerous factors, including wind direction and speed, size and position of openings, outdoor and zone air temperatures, and other relevant parameters.
Within the simple Airflow Network example above, an air flow network is illustrated consisting of three thermal zones (Zone 1, Zone 2, and Zone 3), exterior windows (Window 1, Window 2, and Window 3), and interior doors (Door 1 and Door 2).
Two External Nodes (1 and 2) are identified, each associated with a specific facade and its corresponding windows.
The depicted air flow pattern represents one possible scenario at a single point in time, but actual airflow patterns vary depending on factors such as wind pressure distribution, window and door states (open or closed), and temperature differentials between zones and outdoor air.
Modeling zone pressures due to envelope leakage and forced air distribution during HVAC system fan operation.
Simulating node pressures in a forced air distribution system during HVAC system fan operation.
Calculating multizone airflows driven by forced air, wind, and surface leakage during HVAC system fan operation.
Simulating air distribution system airflows, including supply and return air leaks, during HVAC system fan operation.
Modeling air distribution system node temperatures and humidity ratios during HVAC system fan operation.
Computing duct conduction and vapor diffusion losses during HVAC system fan operation.
Estimating sensible and latent loads on adjacent zones due to air distribution system leaks during HVAC system fan operation.
Modeling zone pressures driven by wind when the HVAC system fan is off or if no air distribution system is specified.
Calculating multizone airflows due to wind and surface leakage when the HVAC system fan is off or if no air distribution system is specified.
Including zone exhaust fans as part of the airflow network.
Calculating zone sensible and latent loads for different supply air fan operation modes, such as cycling fan with cycling compressor or continuous fan with cycling compressor.
Ensuring that when multiple forced air systems are present in the IDF, all systems must be used in the Airflow Network model.
Airflow Networks can take significantly longer than a typical energy simulation. If simulations run for longer than 1 hour, they will likely fail to complete. Contact if extra compute capacity is required.
