Wind Machines

Advantage in numbers

• Wind machines / frost fans are an effective tool for protecting a wide variety of crops from the damaging effects of frost in locations around the world. Other systems such as overhead sprinklers, heaters, or air drains provide some degree of protection but cannot be effectively and efficiently deployed in the vast numbers wind machines can.

Protect crops by raising temperatures

• During radiation cooling nights, wind machines / frost fans pull down warmer air and ventilate the growing area to prevent the pooling of cold air. Most importantly, they provide air movement across the plant surfaces which prevents them from supercooling. On still, clear nights fans prevent the buds from supercooling up to 4° F (2.2° C) colder than ambient temperature. Even on weak inversion nights, Orchard-Rite machines substantially reduce the chance of supercooling.

Forms natural frost protection without affecting crop growth

• Wind machines / frost fans duplicate nature’s natural protection – the wind. Crop damage occurs when the wind stops not only because the temperature drops dramatically, but also because the bud will become 4° (2.2° C) colder than the air temperature. By generating air flow, wind machines prevent this from happening.

Easy to manage

• Wind machines / frost fans are available when needed and can be programed to start and stop as conditions change. They do not affect your growing conditions and can be moved to new blocks when replanting takes place.

No. Wind machines / frost fans have the opposite effect by keeping plant surfaces warmer under still, calm conditions. On cold, calm nights, the plant surfaces radiate their heat and actually become colder than surrounding air temperature. Wind machines / frost fans warm those surfaces by moving air across them every five minutes.

We recommend starting the wind machines / frost fans 4° F (2.2° C) above the critical temperature for the crop being protected.

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. Where bud charts do not apply, in some areas, the industry provides freezer testing of wood to determine critical temperature.

Supplemental heat is used on nights when the forecasted low is more than 4° F (2.2° C) below the critical temperature. The use of supplemental heat can be expected on nights when the sky clears early, the wind dies early and there is a dew point that is 5°+ (2.75°+ C) below the critical temperature. The wind machine / frost fan will circulate the heat through the block and between machines to prevent the heat from dissipating into the air above the crop.

Supplemental heat is most needed on the side of the block where cold air is infiltrating the protection zone, these areas include behind ditch banks, road beds, and in low areas. Heat in this area will be carried into the block by the drift and will help the wind machine / frost fan keep the temperature above critical on the edge. Without the supplemental heat, the temperature on the drift edge will decrease during the night and damage will occur as the machine struggles to keep the temperature above critical. Supplemental heat can be placed in lines between the wind machines / frost fans so the heat can be circulated back and forth to help improve conditions in the entire block.

Many forms of supplemental heat are used, but the most common are under-tree sprinklers, diesel or propane heaters and wood- or coal-fired heaters.

• Under-tree sprinklers - Growers utilize under-tree sprinklers to run large blocks (5+ acres) of water at 40 plus or minus gallons/minute/acre. The heat and humidity generated give an additional 2° (1.1° C) of temperature lift (2 hectares and 375 liters/minute/hectare)
• Heaters - Metal pots heated by diesel, propane, wood, coal, hay, etc. can help the wind machines with an additional 2-4° (1.1-2.2° C) of lift depending on the strength of the system.

• Yes – If the temperature rises 4° F (2.2° C) above critical due to the arrival of clouds or the wind increases to a steady 10+ MPH (16+ KPH). At that point, the wind is providing the same protection that the wind machine provides.
• No – If the conditions are clear and there is variable wind, you should continue to run the wind machines even if you are seeing temperatures well below the critical temperature. Because the machines are preventing supercooling, you are still benefiting the crop with the wind machine / frost fan running.