When crops, particularly salad vegetables, are harvested in the summer months, the crops are at whatever temperature pertains on that day. For the crop to reach the customer it has to be kept fresh and, in order to do this, the crop is cooled very rapidly to between 2 and 4°C. If the crop has been harvested at >20°C, the degree of cooling required to bring the crop to storage temperature will damage the crop.
To counter this, moisture is added during the chill down period. However it is not possible to humidify during the whole chilling period as the duty requirement would be so high that it is not commercially viable. The humidification is therefore timed to operate when the cooling is off, to give a fog in the store so that the crop can reabsorb moisture from the air and also to provide residual moisture to prevent moisture loss from the crop during the next chill cycle.
The normal cycle is 15 minutes of cooling followed by 5 minutes of fogging, this cycle being repeated until the crop is down to temperature. There is no humidity control for this process and control is achieved by using a timing circuit in the plant control panel that runs the humidifier. It is critical that the fans from the chiller plant run all the time during this process so that the air distribution paths are maintained.