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How do Wind Machines work? PDF Print E-mail

During a radiation frost, a wind machine is used to draw down the warmer air in the inversion layer and blow it into the orchard or vineyard. The wind machine needs to blow as much air as it can, to the greatest distance possible.

During the day, the sun heats the earth’s surface. The soil and trees become warmer than the air in contact with them, thus heating the air. At night, the colder air settles next to the ground and the warmer air rises forming the inversion.

Radiant frost occurs when a sudden drop in temperature due to irradiation of the trees and soil causes the surrounding air to cool rapidly. The chilled air settles into the lowest areas in the orchard or growing field causing frost damage.

The earth absorbs heat from the sun during the day and releases it into a colder atmosphere at night. The heat loss is greatest just before dawn and this is usually when the maximum danger of frosts and frost damage occurs.

This release of heat creates an 'inversion layer' of warmer air which can be found from 10-15 metres above the ground.

Wind machines use the warmer "inversion layer" air to protect a crop from frost damage. The wind machine is angled slightly downwards to pull this inversion layer down to ground level to protect the crop from frost damage.

The main principles involved are:

  1. The removal of heavy cold air to prevent stratification and retard frost formation
  2. Allow warmer inversion layer air in to replace the colder air at crop level
  3. Some friction generated heat as the air moves past foliage to replace the 'skin' of colder ambient air.