Using Wind Roses to Track Breezes
Wind roses summarise the occurrence of winds at a location, showing their strength, direction and frequency. The wind roses available on the Bureau of Meteorology website are based on at least 15 years of records, and have been created for the more common 9am and 3pm observation times.
Wind roses show the frequency and direction of wind occurrences and are available for locations all over Australia
Wind directions are divided into eight compass directions. The circles around the image represent the various percentages of occurrence of the winds. For example, if the branch to the west just reaches the 10% ring it means a frequency of 10% blowing from that direction. The scale factor can be ignored when interpreting these wind roses. An observed wind speed which falls precisely on the boundary between two divisions will be included in the lower range (eg 10km/h is included in the 1-10 km/h range). Calm has no direction. An asterisk(*) indicate that calm is less than 1%.
Can wind roses help you direct the breezes into your home?
The Australian Bureau of Meteorology provides wind roses for each region in Australia. They are based on daytime data and don’t address evening and night breezes that are often the main source of cooling.
Cool breezes can come from a range of directions but near the coast are generally onshore. On the east coast of Australia, they are generally north-easterly to south-easterly whereas on the west and southern coasts, they are commonly south-westerly. The predominant cooling breezes in Darwin are from the north-west in the wet season and the south-east in the dry season
You can use a wind rose to learn more about the breezes in a property’s location to help you make decisions when you’re renovating or buying a home.Moving air through the house naturally can provide thermal comfort, which is when you are in balance with your environment, feeling neither too hot nor too cold. It is also a great cost saving solution. It is also healthier as there are no ducts and filters to worry about cleaning as with air-conditioning. Capturing natural breezes will make your home more desirable and cost efficient:
- Air moving through a house naturally can provide thermal comfort, which is when you are in balance with your environment, feeling neither too hot nor too cold.
- Natural air flow is a great cost-saving solution as you don’t need to use as much energy for air-conditioning.
- Ducts and filters don’t need cleaning as with air-conditioning, which is healthier for the home and family.
The optimum in capturing breezes though your home is called is cross-ventilation — pressures generated on the building by the wind drives air through windows or doors on one side of the building through to windows or doors on the opposite side, making sure cool breezes can pass right through the house.
NOTE: Cooling breezes through the house through cross-ventilation is useful for cooling the building. Ceiling fans are best for cooling people if there are no breezes blowing.
Finding the wind rose for your location
The Bureau of Meteorology has wind roses for many locations around Australia. Click on the map below.
When you have found your location you can download a PDF (see sample of Sydney) of the wind rose and measure it against the plan of your house to see whether your home is orientated to capture breezes in summer and how you can take advantage of them to provide free cooling.
Reading a wind rose
- Wind directions are divided into eight compass directions, with north to the top of the diagram.
- The circles around the image represent the various percentages of occurrence of the winds. For example, if the branch to the west just reaches the 10% ring it means a frequency of 10% blowing from that direction.
- An observed wind speed which falls precisely on the boundary between two divisions will be included in the lower range (e.g. 10km/h is included in the 1–10 km/h range).
- Each branch of the rose is divided into segments of different thickness and colour, which represent wind speed ranges from that direction. Speed ranges of 10km/h are used in these wind roses.
- Calm has no direction. An asterisk(*) indicates that calm is less than 1%. The percentage of calm conditions is represented by the size of the centre circle – the bigger the circle, the higher the frequency of calm conditions.
- Feature image credit to ©iStock.com/goldenangel