Cabinet/015 Cabinet Installation Guidelines for VFDs.pdf
Return to Procedures Main Menu
Index: Cabinet
Subject: (15) Installation Guidelines for Variable Frequency Drives
Date: February 29, 2012
Revised February 27, 2019
For units with a service vestibule, VFD’s should be mounted directly to the wall without an enclosure. Ventilation will be accomplished by the vestibule exhaust fan. Care should be taken to maintain fallback requirements for the control panel(s) as well the VFD’s. If, for any reason, the VFD’s must be mounted in an enclosure within the vestibule, the VFD enclosure will require ventilation as described below.
VFD’s may be located in the control panel, only if the adequate space is provided and verified. When possible, VFD’s should be located in the control panel or in an adjacent panel to reduce labor costs. In many cases, however, VFD’s will need to be located in a separate enclosure, not in the control panel. VFD’s should not be mounted in
When selecting a location for mounting variable frequency drives, proper ventilation of the drives must be considered to prevent an over-temperature condition. While installations may differ, ventilation of the VFD mounting location requires a source of air and means to move the air.
Air Source: The best source of air to condition the VFD is from the mixed airstream or the return airstream, if these are not available, outside air may be used. Use of outside air should be avoided in high ambient locations where design temperatures exceed 100°F. ABB drives are rated for operation up to 104°F ambient, but can be used in ambient conditions up to 122°F if the VFD is derated to 90% of its rated capacity in amps. Air from downstream of the cooling coil should not be used as it is a saturated airstream. Also, air from inside the condensing section should not be used due to the excessive temperatures. The air source is normally filtered to prevent any build up of dust on the drive. The mixed airstream is typically filtered by the unit filtration prior to the blower section. When the VFD is installed in the return air section, the VFD is normally mounted in an enclosure with a 12” x 12” permanent mesh filter mounted in the bottom of the VFD enclosure. When the VFD is ventilated with outside air, the 4” x 4” mesh filters that we use for our control panels are installed in the intake opening of the VFD enclosure door.
Air Mover: The best means to move the air through the VFD enclosure is to use the supply or return air blowers of the unit. Pathways into the VFD enclosure to the positive and the negative pressure sides of the blowers must be provided to create flow through the enclosure. When possible, the opening or pathway to the positive side of the blower should come into the bottom or near the bottom of the enclosure and the opening or pathway to the negative side of the blower should come into the top or near the top of the enclosure, above the top of the VFD. When using control panel fans, the minimum airflow must be determined. For ABB drives, the minimum airflow is listed by drive model number in the User’s Manual. The control panel fan is rated for 105 cfm.
Enclosure: The VFD enclosure must be sized to allow clearance around the VFD according to the VFD manufacturer’s recommendations. For ABB, a minimum clearance of 8” is given above and below the drive. In general, VFD’s should not be placed directly above another drive. The VFD enclosure should also as tall as possible/practical to allow the ventilation air to exit the enclosure above the VFD’s to avoid trapping heat in the top of the enclosure. Any additional space that can be provided above the VFD is beneficial. The enclosure must be sized to allow the VFD bypass components to be mounted with the VFD, if so equipped.
NOTE: When using VFD manufacturers other than ABB, please consult the manufacturer’s data for specific information regarding temperature ratings, airflow requirements, clearances, etc.
