Next in our line of electric control accessories is time delay switch. It allows the fan to run for a period of time after it was manually shut off or de-energized. It offers the advantage of ensuring the fan is not consuming an unnecessary energy. Motion sensors or timers within the switch provide this capability. A time delay switch is commonly used in restrooms, offices and conference rooms.
Next are speed controllers. They vary the fan speed by adjusting the voltage or frequency to the motor. There are two types of speed controllers: single-phase motors with controller and three-phase variable frequency drive or VFD . The single-phase motors with controller works by adjusting the voltage going to the motor. It can be mounted directly in the fan to help balance the system. If it is placed in a remote position, it is used to adjust the airflow.
The three-phase variable frequency drive works by varying the frequency and voltage going to the motor. It is primarily used to vary the speed of the fan. It can speed up or slow down the speed of the fan based on the demand of the system, saving energy and maximizing performance. VFDs are also used to slowly start up larger horsepower motors, limiting the current draw while the motor is coming up to speed.
There are many guard options for ventilators with varying purposes. Their role is to protect the fan from foreign objects to protect the fan from the elements and for personnel safety during operation. These are the common guards found in the HVAC industry: inlet and outlet guards, belt and shaft guards, and motor covers and weather hoods. A motor cover or weather hood acts like a shield to protect the motor, fan or other components from the elements. Inlet and outlet guards keep the foreign objects out of the airstream and help protect the impeller and other components from damage. Belt and shaft guards may be designed to protect the product from damage, the elements and for personnel safety. The most compelling reason for selecting guards is to ensure the safety of people. The Occupational and Safety Health Administration (OSHA) has specific requirements pertaining to guards depending on application. It is important to know that not all guards need OSHA requirements and if required, must be specified.