VE Application Category


Simulate air flow driven by wind pressure and buoyancy forces using a fast multi-zone thermo-fluid solver.

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It Incorporates models of:

  • external wind pressure based on empirical data derived from wind tunnel experiments
  • stack effect (buoyancy)
  • flow characteristics of cracks
  • flow characteristics of window types
  • flow characteristics of large openings
  • two-way flow
  • resistance due to grilles and wall friction
  • Rayleigh instability

Input Data

  • Building geometry passed automatically from ModelIT:
    • Room dimensions and connectivity
    • Co-ordinates of windows, doors and holes used as MacroFlo openings
    • Assignment of opening properties to windows and doors using a simple and efficient editing process based on opening types
  • Opening properties:
    • Wind exposure
    • Crack dimensions and flow characteristics
    • Free opening area
    • Timing and degree of opening
    • Opening controls, expressed as functions of weather variables and conditions in any room
  • Hourly wind speed, wind direction and external air density from weather file
  • Data from ApacheSim and ApacheHVAC building simulation and system thermal parameters can be used

Analysis Options

  • MacroFlo’s flexible input structure allows analysis of problems involving any combination of infiltration, natural ventilation and mechanical ventilation.


  • Studies using MacroFlo can provide:
    • evaluation of natural ventilation solutions
    • evaluation of ventilation control strategies
    • an understanding of the performance of double-skin façades
    • analysis of room temperature statistics in naturally ventilated buildings
    • predictions of air velocities through openings
    • analysis of HVAC systems where the building is used as a return air pathway
  • For each opening MacroFlo calculates:
    • Volume flows in and out
    • Mass flows in and out
    • Effective free area for air flow
  • Aggregated air flows for each room are also available
  • The effect on building and system thermal performance, and the weather data used to drive the simulation can be viewed
  • MacroFlo results are displayed by the Virtual Environment results analysis programs Vista and VistaPro
  • Results are accessed via graphical views of the building, allowing interrogation of data at a hierarchy of levels: building, room, surface, opening
  • Vista and VistaPro displays graphs, tables, monthly summaries, ranges or user-specified synopses
  • Results from MacroFlo include arrows showing airflow in and out of the building and wind rose settings for any time of the year
  • Multiple results can be displayed simultaneously or aggregated
  • Metric and imperial units are available
  • Graphical and numerical data can be exported to Excel, Word and other applications
  • Demonstrate how to reduce the need for air conditioning using natural / mixed-mode strategies.
  • Analyse all aspects of bulk airflow: infiltration, natural ventilation, facade design, mechanical ventilation.
  • Simulate air flow processes over different periods – from a single day to as long as a year.
  • Evaluate feasibility of strategies such as: single-sided ventilation, cross-ventilation, whole-building ventilation, chimneys, opening controls and window opening category.