What are the best strategies to optimize natural ventilation in passive house projects?

1 Climate analysis

The first step to optimize natural ventilation is to understand the climate of your location and how it affects the temperature, humidity, wind, and solar radiation throughout the year. This will help you determine the most suitable ventilation strategy for your project, such as cross ventilation, stack ventilation, or hybrid ventilation. You can use tools such as climate charts, psychrometric charts, wind roses, and sun path diagrams to analyze the climatic data and identify the potential for natural ventilation.

2 Site selection and orientation

The next step is to choose a site and orient your building in a way that maximizes the exposure to prevailing winds and minimizes the heat gain from the sun. Ideally, you want to place your building on a high and open site, with the long sides facing north and south, and the short sides facing east and west. This will allow you to capture the cool breezes from the north and south, while reducing the solar heat gain from the east and west. You should also avoid obstructions such as trees, hills, or other buildings that can block or deflect the wind.

3 Building shape and layout

The shape and layout of your building also influence the natural ventilation performance, as they affect the air flow resistance, pressure distribution, and thermal mass. Generally, you want to design your building with a simple and compact shape, with a low height-to-width ratio, and a shallow floor plan. This will reduce the air flow resistance and create a positive pressure difference between the windward and leeward sides, which will drive the air flow through the building. You should also arrange your rooms and functions according to their ventilation needs, placing the most occupied and heat-generating spaces on the windward side, and the less occupied and heat-sensitive spaces on the leeward side.

4 Window size and placement

The size and placement of your windows are crucial for optimizing natural ventilation, as they control the amount and direction of air flow in your building. You should design your windows with a large opening area, preferably at least 10% of the floor area, and distribute them evenly on both sides of your building. This will create a cross ventilation effect, where the air enters from one side and exits from the opposite side, creating a cooling and refreshing breeze. You should also place your windows at different heights, especially on the leeward side, to create a stack ventilation effect, where the warm air rises and escapes from the upper windows, creating a negative pressure that draws in more cool air from the lower windows.

5 Air flow patterns and control

The last step is to analyze and control the air flow patterns in your building, to ensure that they are effective and comfortable for the occupants. You can use tools such as computational fluid dynamics (CFD) simulations, smoke tests, or tracer gas tests to visualize and measure the air flow patterns and velocities in your building. You should aim for an air flow velocity of around 0.2 to 0.8 m/s, which is considered comfortable and pleasant for most people. You should also provide means for adjusting and regulating the air flow, such as operable windows, louvers, vents, fans, or dampers, to adapt to different weather conditions and occupant preferences.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?