Hybrid (mechanical and natural) ventilation of a school building

Project facts

Type: Educational, whole-building studies
Consultant: EQUA
Client: Betic
Summary: A mechanical and natural ventilation system in a schoolhouse is improved by introduction of a well-designed control system.


Each corridor on every floor of a zero energy schoolhouse is connected to a central staircase. All classrooms and offices are supplied with air directly from the adjacent corridors by use of fans. Depending on various control strategies the corridors are either ventilated naturally or mechanically. The central staircase works as an exhaust duct for both natural and mechanical ventilation.

With no active cooling and only reheat coils in the supply air, pleasant room temperatures and air quality must be maintained whenever a classroom or office is occupied. However, slightly lower temperatures are accepted in the corridors and the staircases.


A key feature to this ventilation concept is a building control system which takes into account all the interactions between various control strategies, the plant, the building, air flows inside of the building and not least the building occupants.

Most of the local controls are fed back to the central building control. Some of the most important local macros in turn control:
  • Storey-wise window ventilation of the corridors according to ambient air temperature, rain and wind, the CO2 content in the corridors, occupancy and ventilation need on all other floors.
  • Overflow fans between corridors and classrooms according to occupancy, room air temperature (for day and night cooling).
  • Storey-wise mechanical supply airflow rate for corridors on each floor according to ambient air temperature, rain and wind, occupancy, CO2-Level, air demand of all other floors and occupancy in multi-purpose hall.
  • Heater convectors in overflow fans (only possible when fans are in operation) according to zone air temperature.
  • Heat recovery in the central AHUs according to air and supply air temperature.

To minimize work on the Advanced Level, fans between corridors and classrooms where modelled with central AHUs.


The model was used to:
  • Verify and improve the control strategies for ventilation, heating coils and the plant.
  • Adjust the window opening size for natural ventilation.
  • Size a number of building services, such as an air to water heat pump and the reheat coils.


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