Cross ventilation is one of the most effective ways of naturally cooling a house. Houses in hot, humid climates like the tropics can become hot and unbearable.
As a wind-driven strategy, cross ventilation uses wind or breezes to move air through a room. Hence, reducing the temperature in a house significantly.
Before air conditioning, cross ventilation and other passive ventilation strategies kept homes cool and comfortable. These strategies still work for houses in several tropical regions around the world.
They can also work for you in your home.
What Is Cross Ventilation?
Cross ventilation is a form of natural ventilation that allows wind to enter one side of a room and out another. Ideally, cross ventilation uses wind-driven force to bring cooler air from outside and replace the stale, warm interior air.
How Does Cross Ventilation Work?
Wind generally moves from high pressure and seeks out areas of low pressure.
When wind impacts your house from the windward side (side facing the prevailing wind direction), it creates positive pressure. Openings on the leeward side (the side opposite the prevailing wind direction) are usually in negative pressure since the wind is flowing away from it.
Therefore as the wind enters the room from the windward side, it flows on a path that leads it to exit on the leeward side.
This constant movement of wind through a room creates cooler indoor temperatures.
Why Is Cross Ventilation Important?
Cross ventilation is one of the most effective methods of natural ventilation. It moves more air through a room than other forms of natural ventilation, like single-side ventilation or the stack effect method.
Ideally, cross ventilation is best for regions and sites that have access to wind or breezes. Once breezes are available, cross-flow ventilation is one of the easiest and best ways to naturally remove stale air from a room. This process replaces the stale air with fresh and cooler air.
In addition, cross ventilation helps remove odours and moisture, which create mould in your house.
It also helps you achieve better thermal comfort in your home.
Effective natural ventilation methods also reduce reliance on mechanical systems like air conditioning. Hence, like many good tropical architectural design strategies, it is more sustainable.
Cross Ventilation Versus Single-Sided Ventilation
Single-sided ventilation is when there is only one opening in the room. This opening can be a door or a window.
Cross ventilation has a higher air-exchange rate than single-sided ventilation.
Single-sided ventilation occurs when the door is typically unopened in rooms with a window and a door. However, if the door and window are always open, you will get cross ventilation.
Having an operable window in a room is better than no window. However, having more than one window or door is better for better air exchange.
Strategies For Cross Ventilation
They are a few fundamental principles and strategies for cross ventilation to occur effectively.
Two Minimum Openings
For cross ventilation to work, at least two openings (windows or doors) must be in the room. Wind needs to have an inlet and an outlet.
It works best when at least one opening faces prevailing winds and the other opening on the opposite side of the room.
These openings can be windows, doors or vents. For example, you can have a window on the windward and another on the leeward side of the room.
Alternatively, a window might face the prevailing wind while a door may be on the opposite wall.
This strategy is beneficial where a room may have only one exterior wall. Hence, that wall may be the only location for a window. Therefore, the door in the room can be the second opening for air to have an outlet. Keep in mind that this door needs to be open for air to flow through.
Short Distance Between Openings
Shorter distances between the openings in a room or home are ideal for adequate cross ventilation. Since the wind travels from one side of the room to the other, it is better when the travel distance of the wind is short.
As a room gets deeper, the wind will slow down and become less effective when it blows across your skin. Ideally, the distance should be as short as practical to be most effective.
Parts of your home that are one room deep will have the most potential for adequate cross ventilation. For instance, having a space with windows on the windward and leeward sides of the room will have a lot of air movement. However, this situation is more effective when the distance between the two sides is short.
Research suggests this can work for spaces up to 12m or 40 feet wide. However, I would aim for less than half that distance in a home.
In homes that become too wide, introducing a courtyard is useful. This strategy will decrease the distance wind has to travel.
Unobstructed Paths For Wind
A clear, unobstructed path for the wind to flow through the room is also an excellent property for cross ventilation to work well.
Obstructions like walls or partitions will impede wind flow through the room. These obstructions can slow down or block wind from passing through your home.
However, walls can also change the direction of the wind flow. Hence, using walls or screens to change the direction of the wind can be an advantage or disadvantage. It will depend on where you want the wind to go.
Position of Window or Door Openings
The position of window and door openings is essential for adequate cross ventilation. These locations for openings help determine where in the room breezes are likely to flow.
Ideally, the wind blowing through your home should flow around areas you and your family are likely to be inside the room.
For example, in a living room, breezes should pass where you sit in that room. Therefore, the location of openings should allow wind to enter your living room from the windward side. That wind should be able to flow through the sitting area in your living room before exiting another side of the room.
Hence, this cooler air from outside can move across your body while you are in the room. This arrangement promotes good thermal comfort for you, your family and the other people in the room.
Avoid positioning windows and doors where the wind passes through a part of the room that you do not use. An example could be a corner or one side of the room.
Size and Quantity of Window or Door Openings
The size of openings can also influence the quality of cross ventilation in your home.
Larger window openings allow more are to flow into and through a room than smaller openings.
However, they are techniques combining small and large openings to create better cross-flow ventilation in a house. For instance, it is better to have smaller windows on the windward than your leeward side. This strategy may sound counterintuitive, but theoretically, it increases the velocity of the wind inside the room.
Advantages Of Cross Ventilation
Improves Thermal Comfort
Cross ventilation improves the thermal comfort in a hot tropical house. In the tropics, the inside of a home can become very hot and uncomfortable without proper ventilation.
As a result, cross ventilation can significantly reduce the indoor temperature of your house. In addition, carefully positioning windows and doors can direct wind flow to the parts of the room where you need it. Wind blowing over the skin of the people occupying a room will significantly improve their perceived thermal comfort.
High Air-Exchanges Rate
It is vital to replace stale air inside a room with fresh air from outside. This process improves the indoor air quality of your home or building.
Using cross ventilation is a great natural way of creating a healthy air exchange in your house. It helps remove any odours, toxins and other airborne contaminants.
Removes Moisture
A house that is sealed and has poor ventilation can trap moisture. This moisture can encourage mould growth.
Maximising air movement through cross ventilation removes moisture from your home. Hence, reducing the chance for mould or any other moisture issues to develop.
Does Not Rely On Mechanical Systems
Cross ventilation is a natural form of ventilation. Hence, it does not need any mechanical ventilation systems.
Mechanical cooling systems like air conditioning relies on electricity. Furthermore, they consume a lot of electricity and are often the highest energy consumer in a home.
Using cross ventilation consumes no electrical energy. They are passive and, as a result, it is more sustainable.
Disadvantages of Cross Ventilation
Depends on the Amount the Wind
Cross ventilation uses natural breezes to get air movement in a home or building. Therefore, it will be harder to promote cross ventilation on hot days that do not have a breeze.
However, on days with less breeze, fans can help increase air movement and help to keep you cooler.
Depends on Good Outdoor Air Quality
Your windows or doors need to be open for cross ventilation. However, if the outdoor air quality is poor, that air will flow through your home.
Bad air quality can include smoke, chemicals and foul odours.
My previous home had louvres over the windows and doors. These were great as they could always stay open for constant air movement.
However, there are plenty of cane and bush fires in the dry season. Therefore, we had to close all of the windows. Closing the windows meant no cross ventilation.
Affected by Rainfall
For the best results from cross ventilation, windows or doors on the windward side so be open. However, the windward side is where the rain comes. Hence, the windows that let in breezes also allow in the rain.
As such, during rainfall, you will have to close windows that do not have a protective covering from the rain. Therefore, you will lose access to that source of natural ventilation.
It is a good idea to have some shelter like hoods, patio roofs or overhangs that will help protect windward windows from direct rain.
You could also use windows like jalousies or even awnings in some locations. These windows can limit the amount of rain that enters. They also allow some breeze to flow in and through your rooms.
Best Windows For Cross Ventilation
Windows that maximise the ventilation opening are ideal for cross ventilation. Many popular window types like sash, sliding or awning windows allow less than 50% of their opening.
In tropical countries, it is best to use windows that permit as much of their opening for natural ventilation. This condition helps optimise cross ventilation.
Your window selection helps increase flexibility by controlling and redirecting airflow. The window type, size, and location can also help increase or decrease airflow velocity. Hence, these can maximise the natural air movement in your house.
Louvre or Jalousie Windows
Jalousie or louvre windows allow wind to flow through almost 100% of their physical opening. Their thin blades and frame do not restrict a lot of wind from blowing into your room and home.
However, jalousies and louvre windows have other benefits for natural ventilation.
Adjusting the blades on a louvre window can also help keep the rain out while allowing cross ventilation.
In addition, the angle of the blades assists in directing the wind upward, downward, or straight through your room.
Casement Windows
Casement windows also allow nearly 100% of the window area for passive ventilation.
In addition, casement windows are excellent at redirecting the wind into your house.
Where the prevailing winds blow parallel to the window, the casement window leaves act like fins which capture and redirects the wind.
Therefore, casement windows are ideal where you must redirect wind to maximise cross ventilation.
However, you will usually have to close casement windows if the rain begins to fall. Rain can easily pour through an open casement window.
Bifold Windows
Similar to casement windows, bifold windows allow almost all of their opening to natural ventilation. They can also assist in redirecting the wind into your room.
Another benefit of bifold windows is they can create wide openings. The increase in width and overall size of the window opening is a great plus for promoting natural ventilation.
However, like casements, bifold windows let in a lot of water during rainfall.
Conclusion
Natural ventilation is one of the most critical aspects of designing a house in tropical climates. Cross ventilation is one of the most effective natural ventilation methods.
They are many benefits of cross ventilation in any tropical home, including greater air exchange and thermal comfort. Following strategies like having two openings and short, unobstructed spaces between opposite walls will help increase wind flow.
Proper cross ventilation techniques are efficient and sustainable strategies for any modern design in the tropics.
Reference:
Cross ventilation – Wikipedia