Natural ventilation

The module to simulate natural ventilation using the multi-zone model (mzm) is for the time being in beta test and results obtained using this module must, as always, be looked upon with natural skepticism.

Any feed-back to the module given at bsim-support@sbi.dk is appreciated!

The tab Natural Ventilation gives access to definition of parameters for the opening/WinDoor to simulate natural ventilation (airing) based on differences between indoor and outdoor temperatures as well as wind speed and wind direction.

2nd tab in the WinDoor property dialog gives access to define parameters for simulating natural ventilation.
2nd tab in the WinDoor property dialog gives access to define parameters for simulating natural ventilation.

Opening

  • Cd: Discharge coefficient determined by the geometry of the WinDoor/opening. Typical values range from 0.62 to 0.7.

  • Cnt: Is the geometrical center of the opening (0-1). The center is located in the distance CntH above the lower edge of the WinDoor, where H is the total height of the WinDoor. Example: For a WinDoor with horizontal opening and fixing at the top, the center of the opening will be located approx. 20 % above the bottom of the WinDoor (rectangular, horizontal opening at the bottom and triangular openings at the sides) and the Cnt*-value is thus 0.2.

  • Afrac: Is the part of the actual opening that can be opened. If Afrac = 0, the opening can not be opened and thus not contribute to the natural ventilation of the thermal zone.

    • The sketch at the right of the dialog illustrates BSim's perception of the opening and the input data.

  • Ka: The inlet air handling unit box constant is used calculation of night cooling by natural ventilation.

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