Saving energy by going natural is the way to go if you are considering constructing a Green Home. One of the aspects of constructing a Green Home is to reduce energy use and costs by resorting to natural ventilation systems rather than the well known mechanical ventilation practices. 

So, what is natural ventilation and how does it work? 

Wikipedia defines natural ventilation as  follows - "Natural ventilation is the process of supplying and removing air through an indoor space by natural means".

Natural ventilation systems rely on pressure differences to drive fresh air through your home. This pressure difference can be caused by the wind or the buoyancy effect created by temperature differences or differences in humidity. In both cases, air moves from a high pressure zone to a low pressure zone creating a circuit with a constant flow of fresh and clean air through the building. 

The two well known natural ventilation techniques are;

1. Cross ventilation

2. Stack ventilation

Let us understand the basic principles of these two ventilation techniques.

Cross ventilation

1. Cross ventilation

The principle of cross ventilation is very simple - you need to have two open spaces (windows, doors or outlets) on the opposite walls of your room which will cause air to flow across the room. 

A more scientific explanation of this would be - air flows from one side of the room to the other due to the pressure difference between the windward side (high pressure zone) and the leeward side (low pressure zone) of the building. The flow also depends on a few other factors such as the window/door size, the distance between the windows/doors and restrictions along the flow path.

Since successful cross ventilation requires analysis of the high and low pressure zones around your house, you would need to discuss the placement of doors and windows with your architect or builder during the design phase. You can spend some time studying where the wind comes from at different times of the day or if possible, at different times of the year to ensure that you place the doors and windows at the right spots. 

Some examples to maximize air flow by cross ventilation are - by placing the patio door across the living room windows and by aligning doors that lead outside to the garden with windows and doorways to create a passage of air flow. After all, your Green Home should be able to reflect the true spirit of being able to save energy in all the right ways!

Stack ventilation

2. Stack ventilation

The principle of stack ventilation is based on the fact that warm air is lighter than cold air which creates a vertical pressure difference in a building. 

Hence, if the air inside the building is warmer than the outside air, it will rise to the roof and flow out of the opening at the top, creating a vacuum at the lower level of the building which will cause the windows and open spaces at the lower level to suck in cool and fresh air from the outside - thereby creating air movement throughout the building. 

On the other hand, if the internal air is cooler than the external air, the cooler air will flow out of the openings at the lower level and warmer air will flow in from the roof top. This flow of air is also known as 'convective flow due to the stack effect'.

There are two factors to consider to obtain cooling by stack ventilation;

1. The incoming air must be cooler than the internal temperature, hence the air that is drawn into the lower levels must preferably be from a shaded or a landscaped region or from over a body of water.
2. There must a certain height difference between the windows used for the inlets and outlets.

Again, these are points which need to be discussed with your builder during the design phase. Moreover, depending on the landscape and the wind and temperature conditions of your site, your builder will be able to tell you whether cross or stack ventilation would work better in keeping your home cool. However, in most cases, the same openings may contribute to both the methods of natural ventilation and we cannot completely isolate one from the other!

One of the methods to enhance stack ventilation is by constructing a solar chimney. A solar chimney is a vertical shaft with an opening at the top through which air flows and is heated by the sun's radiation during the day. This facilitates stack ventilation naturally because it increases the temperature difference between the incoming and outgoing air which in turn enhances the movement of air through the building.

Benefits of natural ventilation

Why should your Green Home be naturally ventilated?

1. Zero energy consumption which automatically reduces costs.
2. No operating costs required to set up and maintain mechanical ventilation techniques.
3. Lower initial costs and lower maintenance over the years.
4. Increases the indoor air quality and promotes a healthy, comfortable and productive lifestyle.
5. Provides a psychological benefit to the building occupants since it connects with the outside in a natural way.