Spring frosts can be a major problem in cool climate wine areas. To achieve frost protection on our vineyard we use a tractor driven, 10m high rotating fan, and on the remainder we have overhead sprinklers. Our experience is that in most, but not all situations, the sprinklers offer superior protection to the overhead fan. However, they require a lot of water to effectively cover the area, and when it is very cold the rate at which the water is applied needs to be adequate. In these conditions, and when a very strong inversion is present, the fan can out perform the sprinklerrs Technical information on how these work is available in this article.
A layer of ice builds up on the vine. The freezing water releases heat, warming the vine and keeping it from damage. More water is needed as the outside temperature drops further below zero.
The icicles can get quite large, depending on how long the sprinklers are on. In the morning all the ice must melt before switching the water off. If the sprinklers are turned off before the sunlight melts the ice, the melting ice will take heat from the vine, causing damage.
The sprinklers are set to deliver at a rate of 3mm per hour. If it gets too cold, frost damage may still occur unless the rate is increased.
The fan is 10 metres high and rotates. Warmer air from ten metres up is mixed with the colder air at the surface