When designing a new house or renovation it is important to consider how a design can minimise its reliance on mechanical ventilation – air conditioning and heating. Buildings consume more energy and contribute more green house gasses emissions than any industry. Our homes therefore offer us an opportunity to reduce our impact on the environment more so than any other action we take.
I spoke in the last blog post on Environmentally Sustainable Design (ESD), that the starting point for creating energy efficient homes is using the sun for free heating, and blocking it in summer to reduce the need for air conditioning. The next step in the design process is to take advantage of passive cooling via a design principle known as cross ventilation, which provides free cooling in summer.
We all eagerly anticipate those afternoon cool changes that bring welcome relief to Melbournians after a hot summer’s day. The design of your house is critical to its ability to use those breezes for free cooling.
In Melbourne cooling summer breezes always come from the South. Our first step is to ensure we have no obstructions along our southern boundary such as a large tree or building blocking access to these breezes. See the diagram from my book below.
If you do have such obstructions it is important to position parts of the house away from these, aligning yourself alongside a point at which you have clear access to these breezes. If looking to buy a block, try find one that you dose not have any tall obstructions. See the diagram below.
To benefit from cooling winds, it’s important to understand that passive cooling or cooling from breezes will only enter your house if the wind can exit out the other end. Think of blowing into a tube: if you then place your hand over the end of that tube the air can’t move. To flush out the built up hot air inside the house, your spaces must be designed for the wind to enter in one end and out the other. See the diagram below. This is what a good architect will ensure when designing your home.
The next aspect to consider is that your house needs to be narrower between the southern external wall and the northern external wall. Or put another way: one room deep as apposed to two. This means you have no walls internally that will obstruct the breeze flowing in from the southern side and out the northern side; allowing the cooling breezes to flush the heat build up within the house during the hot day.
A trick to cool your house faster, or speed up the process should the breeze be light, is to open the windows on the south side half as much as on the opposite north side. This constriction causes the air passing through your house to accelerate moving faster than its speed outside. This is an adaptation of the ‘Venturi effect’ named after Giovani Venturi (1746 – 1822) an Italian physicist. It is most commonly used in machinery and racecar aerodynamics, but we can create the same effect in your home too.
Be sure when renovating or building your new house that your architect is applying cross ventilation into the design.