circuit with capability to isolate the VFD when in the bypass mode. Transfer to the bypass mode shall be automatic in the event of VFD failure or for specific trip conditions allowing safe transfer of utility voltage to the motor. Automatic bypass with an earth ground condition is not allowed. The bypass contactor shall be cycled on and off while operat- ing in bypass, to maintain the set-point temperature of the cold water. The drive design shall be operated as a stand-alone system without the need for a BMS sys- tem. Operator controls shall be mounted on the front of the enclosure and shall consist of start and stop control, bypass/ VFD selector switch, Auto/Manual selec- tor switch, manual speed control, and solid-state temperature controller. An emergency bypass selector switch inter- nal to the panel allowing the fluid cooler fan motor to be run at full speed shall be furnished. To prevent heating problems in the fluid cooler fan motor and to assure proper gear box lubrication the VFD sys- tem shall de energize the motor once 25% motor speed is reached and cool- ing is no longer required. The VFD shall include de-icing logic with auto canceling and adjustable time. Speed in De-Ice mode shall not exceed 50% motor speed. The fluid cooler manufacturer shall supply VFD start-up assistance. Tower vibration testing throughout the speed range is required to identify and lockout any natural frequency vibration levels which may exceed CTI guidelines.
Vibration Limit Switch:
5.8Add the following paragraph in the Mechanical Equipment section: A single-pole,double-throw vibration limit switch in a NEMA 4 housing shall be installed on the mechanical equipment support for wiring into the owner’s control panel. The purpose of this switch will be to interrupt power to the motor in the event of excessive vibra- tion. It shall be adjustable for sensitiv- ity, and shall require manual reset.
■Unless specified otherwise, a Metrix switch will be provided. A double-pole, double-throw model is also available. If purchased in con- junction with the Control System, it is also factory-wired. The requirement for manual reset assures that the tower will be visited to determine the cause of excess vibration.
