Frost Prevention Fans

This article is written by Hiroki A.

As we enter the latter half of March, the weather has begun to reflect the coming of spring with its typical pattern of "three cold days followed by four warm days." During this season, an important task in managing tea fields is checking the operation of the frost prevention fans.

Frost prevention fans are devices designed to protect new tea shoots from frost during the early tea harvest season. They are shaped like large fans mounted on tall poles, resembling utility poles. On clear mornings in the new tea season, radiative cooling can cause the temperature near the ground to drop below the air temperature, resulting in frost. This frost can freeze the new shoots, causing frostbite damage. To prevent this, the fans blow relatively warmer air from above down to ground level, helping to keep the new shoots from freezing.

These fans are equipped with automatic systems that detect the ground-level temperature and activate when it falls below a set threshold. Thanks to this automation, tea farmers can sleep soundly even on early mornings when frost is expected.

Today, frost prevention fans are widely used in many tea fields. However, they weren’t always so common. It was only after the severe frost damage in 1979 and 1980 (Showa years 54 and 55) that their effectiveness became widely recognized, leading to their nationwide adoption. Although the installation cost is high, the fans are a highly effective way to reduce frost damage, which can otherwise cause losses amounting to hundreds of thousands or even millions of yen in just one night. As such, they have become a common investment in modern tea farming.

However, these fans must be properly maintained and functioning to be effective. Their operation period is from March through May, when the risk of frost damage is highest. Outside of this season, the circuit breakers are turned off, and the fans are left dormant, requiring a restart at the beginning of each new season. At that time, it is essential to check that each fan is operating correctly.

Since there are often multiple fans in one field, each one must be checked individually. A frequently overlooked detail is whether the fan's oscillating motion is working. The oscillation is extremely slow, so it must be observed carefully to confirm. This part is also prone to malfunctions—this year, issues were found in two units. These operation checks must be completed by the end of March, and any defects discovered must be repaired promptly before frost damage can occur.