PNNL

Abstract

An experiment in a vineyard in south-central Washington is described in which a vineyard wind machine used for frost protection was turned on and off while monitoring the air temperature in the vineyard. The wind machine fan, with a hub height of 12 m, rotated around a quasi-horizontal axis that was tilted downward into the vineyard at an angle of 6 degrees. The fan also rotated around a vertical axis once every 4 minutes to protect a roughly circular area surrounding the wind machine tower. A temperature inversion of about 3.5°C occurred above the vineyard between the 3-m and hub-height levels during the experiments. The 300-m diameter warming footprint of the fan was displaced down the south-facing 1-2° slope of the vineyard when the ambient wind speed was low, showing the effect of the weak and shallow nighttime drainage flow that often occurred in the vineyard. When the ambient wind speed increased, the footprint was displaced downwind and downslope of the tower. The mean warming footprint magnitude when the fan was switched on was about 1-2°C, and the temperature excess in the footprint relative to the surroundings dissipated quickly when the fan was switched off.