Natural or passive ventilation is one of the primary concerns of a tropical home. How good the passive ventilation in your home is, will determine the level of reliance on mechanical ventilation systems in tropical climates.
What Is Passive Ventilation?
Passive ventilation is the process of naturally moving air through an indoor space. It involves removing stale air from a room and replacing it with fresh air from the exterior. This is done without the use of mechanical systems and relies entirely on natural forces.
They are two types of natural ventilation you can use in your building. These are wind-driven and buoyancy-driven ventilation.
Wind-Driven
As the name suggests, this uses the forces of the wind. It is the wind flowing through an open window or door, due to the difference in pressure.
The most common type of wind-driven ventilation we hear about is cross ventilation. However, you can also have single-sided ventilation, but it is not as effective.
Cross ventilation is when wind enters a building from the windward side and exits through another.
You can design the path the wind is most likely to take. This is dependent on where openings are located and the obstacles, like walls. It is ideal to avoid having any obstructions along that path.
Buoyancy Driven
Buoyancy-driven ventilation uses the density of air to promote air movement in a room. This is due to the difference in temperature or humidity of the air inside compared to outside.
As air enters your home, it heats up and becomes less dense than the cooler air on the exterior. As a result, the warmer air rises. Think of a hot air balloon.
When that hot air rises and has a place to exit the building at a high level, like a clerestory window or roof vent, it naturally pulls in cool air from lower-level openings to replace it. This is referred to as the Stack Effect.
This method of natural ventilation, though not common today in the Caribbean, was a feature in traditional homes, like the chattel house in Barbados. It can be effective especially at times or in locations that do not have a lot of wind.
However, it sometimes does not move air at sufficient speeds to effectively cool people, but it can reduce the indoor temperature.
Passive Ventilation Strategies
So, you may be thinking that all you need to do is to ensure that each room has at least one window and that it is opened, right? You probably did not need to read the last few hundred words to know this.
Essentially you would be right. Once each room has at least one window and that window is opened, then you are likely to get some level of air movement. But in the tropics, it is a good idea to aim for a bit higher than just some level of air movement, to maintain good thermal comfort indoors.
There are a few things that you, as an existing or future homeowner, can consider to maximise the natural ventilation in your home.
1. Small Inlet, Big Outlet
Opening your windows on the windward side a bit smaller than the ones on the leeward side will create a type of vacuum effect. This increases the speed of the air flowing through your room.
2. Bottleneck
When wind flows into a large space, like a patio or a large recessed area outside your wall, and then through a smaller opening, that air is forced to squeeze through that smaller opening. This increases the velocity of the wind flowing into your room.
3. Openings At Diagonal Opposites
It is ideal to have windows open on opposite sides of the room. This allows wind to flow from the windward to the leeward side. Ideally, these windows should also be at opposite corners of the room so that the wind crosses more area of that space.
4. Clerestories and Roof Vents
Consider incorporating high-level clerestories such as jalousies or louvre windows or ceiling, roof, or gable end vents into your design. Jalousies will allow hot air to escape and provide an avenue for cooler air to enter at low-level windows and doors.
5. Top Vents
If you do not have clerestories or roof vents in your project, try using windows with vents at the top. This could have a similar effect as it gives hot air a place to escape, especially if they are near the ceiling level.
Also, you can put vents at the top of doors or even in separating walls. This will allow both wind and hot air to flow from room to room and eventually find its way out.
6. Casement Windows
Casement windows are a good option for redirecting the breeze through your window and into your space. For example, if your wind comes from the east, but your casement window is on the north wall, having the window hinged on the left will allow your window to catch and redirect some of that easterly wind.
Also, the wind can sometimes come from different directions. In Barbados, the wind generally comes from the east. However, it can sometimes come more from the north or the south. Double casement windows are great at redirecting that wind into your rooms.
7. Distance To Travel
It is best to have short distances for air to travel from one end to the other. A narrow building where the longer side is oriented perpendicular to the prevailing winds is best. Having one-room deep spaces is ideal though not often practical.
8. Courtyards
A courtyard can also be a good way to reduce the distance wind has to travel through a home. In the right location, it can reduce the travel distance of the wind significantly. It also provides an area for warm interior air to escape.
Conclusion
Having a house that is cool and comfortable is an essential part of tropical architecture. Passively ventilating your house is ideal for the tropics. Though this is common for us in tropical regions, they are strategies that you can use in your new project or even your existing home that can promote it even better.
Understanding how air moves through your home and ways you can increase air movement is good to know for maintaining good thermal comfort throughout your house.
These, along with other tropical design principles, are ideal for ensuring your comfort and happiness in your home.
Related topics in this series:
Find out all the major principles of designing a house in the tropics.
Or explore more of the other topics in this series.
Site Orientation: The orientation of your home on its site dictates how well it responds to passive design principles.
Shading Strategies: Reducing the solar heat gain in your home can create a better thermally comfortable home.
Passive Ventilation: Natural or passive ventilation is one of the primary concerns of a tropical home.
Wall Materials and Construction: In hot, humid climates, your wall materials need to perform various functions.
Roof Design: Choosing the right roof in hot tropical climates is essential to minimize heat gain.
Exterior Spaces: Making outdoor spaces and nature part of tropical homes is ideal.
Water and Energy Efficiency: With climate change, renewable energy and water resource management are crucial.