Best practice - Bulk
Conventional applications of CIPC to bulk stores, without fans operating, can result in uneven distribution of the treatment. Some areas in the store may receive little chemical, resulting in earlier regrowth and the need for further applications. A better procedure involves low-speed recirculation of CIPC fog through bulk piles. This can significantly reduce the total dose of CIPC required over a storage season by providing a more even distribution of sprout suppressant.
To use the technique, some changes to storage ventilation equipment may be needed – recirculation must be carried out with fans operating at lower speeds than normally used for ventilation.
The principle is for CIPC fog to be recirculated through bulk piles of potatoes using the store’s ventilation system. To prevent the chemical depositing on fan blades and guards, the fans are operated at low speed by connecting them to a variable frequency drive.
Before application, the airflow into lateral ducts must be balanced. Otherwise the smaller volume of air displaced can result in an uneven distribution of chemical. Recirculation is carried out continuously during and after CIPC application, until the fog has cleared.
Variable frequency drives
Variable frequency drives (VFDs, also known as inverters or variable speed drives) are available in a range of capacities and can be configured in different ways:
A single fan or all fans, where these are in sets, may be operated by the VFD. As a basic rule, the more fans that are operated by the VFD, the better, as fans will be operating at lower speed to obtain a given airflow rate.
Just two fans can operate from a VFD, from a set of four supplying a main duct. But any fans not operated by the VFD must be fitted with effective backdraft dampers to prevent short-circuiting of fog and air.
Low air speed considerations
Note that a minimum fan speed limit may be imposed by the manufacturer as sufficient airflow is required for effective cooling of the fan motor.
Slowing the fan down gives it a more gentle action resulting in less turbulence and consequent fall out of CIPC on the fan itself. Even at low speed some CIPC will become attached to fan blades and guards, so it is important that guards are not too fine as blockage could result. Deposits should be friable and are easily removed by running the fans briefly at full speed.
USE PLANT PROTECTION PRODUCTS SAFELY. ALWAYS READ THE LABEL AND PRODUCT INFORMATION BEFORE USE.