The Science of Frost

How does a frost fan work?

 

The most common type of frost formation in Australia is Radiation Frost. This occurs mainly after a day with clear skies and little or no wind. The ground loses heat by radiation and with no clouds to keep the heat it rises up. Cold air is denser than warm air and it sinks to the ground.

The air-cooled near the surface flows downhill like a liquid with the force of gravity. The cold air will pool in hollows and low lying areas.

The warmer air rises and forms an inversion layer about 9-60 m above the ground depending on the topography.

 

 

How a frost fan works

A frost fan works by mixing the warm air from the inversion layer above with the cold air near the ground. Mixing the warm air into the crop level raises the temperature of the air near the crop. The task of the frost fan is to raise the temperature above the critical temperature where crop damage can occur. Different plants have a different critical temperature and the frost fan is set to turn on 2 degrees above the critical temperature for the plant. The Chinook frost fan because of the efficiency of the unique fixed wedge on the blade brings more warm air down from the inversion layer than any other fan.

Do Frost Fans work? Frost fans work on a radiation frost where warm air in the inversion layer can be used to bring the warm air down to the crop level. If there is a black frost which doesn’t happen very often in Australia they will be of little benefit. Find out more at the Bureau of meteorology

 

Listed below are other methods of Frost Protection that can be used in conjunction with Frost Fans

Choice of site

Choose a site for plantings less prone to frost

Higher Slopes

Avoid low pockets and cold spots

Remove trees and obstacles that stop the flow of cold air drainage. Trim lower branches or remove trees completely.

Direct the air to drain out of an area if possible

using for example bushes, mounds of soil or haybales

Canopy Trees can help but be careful that they don’t obstruct the flow  of frost and cause the frost to pool near your crop

Irrigation

In crops where water is available and too much water will not cause damage to the roots Irrigation can be an effective tool for frost protection

The application of water can protect the plant tissue by releasing latent heat energy

More information is available on our useful links post on this website

Heaters

Can be used in conjunction with Frost Fans but are more costly to run.