On top of box-coolers
High temperature (HT) box-coolers normally need not be protected, the tube bundle of these coolers becomes so hot that there is hardly any fouling.
Low temperature (LT) or LT/HT box-coolers do need protection, especially against the blue mussel and barnacles.
For the ultrasonic system to function properly, you need to start with a clean box-cooler. Box-coolers already fouled by mussels, barnacles and the like will not be cleaned by the system. The system stops these organisms from settling. To avoid fouling, the system must be switched on permanently.