FAQs
Q. Why have frost fans proven to be so successful in protecting crops?
Frost fans are an effective tool for protecting a wide variety of crops from the damaging effects of frost. Frost fans protect crops by raising temperatures. They pull down the warmer air on radiation cooling nights and ventilate the growing area to prevent pooling of cold air.
Most importantly, only frost fans provide air movement across the plant surfaces that prevents them from supercooling. On any still, clear night, fans prevent the buds from supercooling up to 2.2°C colder than ambient temperature. Even on weak inversion nights, frost fans substantially reduce the chance of supercooling.
Frost fans are a natural form of frost protection that does not affect the growing environment or the crops. Frost fans duplicate nature’s protection – the wind. Most growers have experienced nights with temperatures at or below critical levels and if the wind continues to blow, they see minimal damage. The damage occurs when the wind quits not only because the temperature drops dramatically, but also because the bud will turn 2.2° C (4° F ) colder than the air temperature.
Frost fans:
- Frost fans are easy to manage.
- Are available when needed
- Can be started and stopped as conditions change
- Do not affect growing conditions
- Can be moved to new blocks when replanting takes place
- Hold a high market value when selling farms or liquidating equipment
Q. Do frost fans create a “wind chill” effect on crops?
No. Frost fans have the opposite effect by keeping plant surfaces warmer under still, calm conditions. On cold, clear, calm nights, the plant surfaces radiate their heat and actually become colder than ambient air temperature. Frost fans warm those surfaces by moving air across them every five minutes.
Q. At what temperature should the frost fan be started?
Because of the supercooling that takes place when the wind dies, we recommend starting the frost fan 2.2° C (4° F ) above the critical temperature for the crop being protected.
Q. What do you mean by the “critical temperature”?
Critical temperature is the temperature expected to inflict at least 10% mortality in the buds, fruits, canes, or woods, depending on the crop. In tree fruit crops such as apples, pears, peaches or apricots, specific tables have been created after testing that identify the expected 10% kill temperatures. In some areas, the industry provides freezer testing of the wood to determine the temperature limits of the various crops during dormancy periods where the bud charts do not apply.
Q. Why can't I just use under tree Sprinklers? The heat and humidity generated from under tree sprinklers give an additional 2° (1.1° C) of temperature lift (2 hectares and 375 litres/minute/hectare) but this by itself might not be enough. Combining both under tree sprinklers and an Orchard-Rite Frost fan can be the best way to save a crop in heavy frosts. Sometimes too much water can damage the roots of the crop.
Q. Why not use Heaters for frost protection. – Hot air rises so the heat is lost to the atmosphere however heaters can be used in conjunction with frost fans as the frost fan can help bring that heat down again. Metal pots heated by diesel, propane, wood, coal, hay, etc. can help the wind machines with an additional 1.1-2.2° C (2-4° F) of lift depending on the strength of the system.
Q. Once started, should the frost fan ever be turned off during the night?
Growers Services equip all the frost fans they import into Australia with the AutoStart option so the Frost Fans do not need to be turned off as you can choose the temperature that turns the machine on and off. The Frost Fan turn on and shuts down automatically when these temperatures are reached.
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