Although modern day Variable Speed Drives (VSD’s) have become more compact, more reliable, more user friendly and more efficient; they all still have losses (W). With most VSD manufacturers now claiming that their products are around 98% efficient, how we limit and control the heat from these losses is the challenge.
Danfoss have a unique back channel cooling feature in their drives that combats this, read more to find out how this concept works and ensures maximum efficiency. The back channel cooling system is standard on Danfoss high power drives, whether you choose IP20 for mounting within an enclosure or IP54 for wall mounting or floor standing.
While high enclosure IP ratings are readily available, allowing the VSD to be mounted outside the control panel; in many industries the norm is to mount the drives within a control panel or MCC. This uses forced ventilation in the form of door mounted fans (and filters) to remove the heat losses from the cubicle and maintain an ambient suitable for the continual operation of the VSD.
This technique does not cause much of an issue for smaller VSD’s, however using higher power drives results in larger heat losses. This inevitably means multiple force vent fans running constantly at full speed regardless of system load, consuming additional energy while creating high acoustic noise levels. Although Danfoss High Power Drives are now designed up to 98% efficiency levels, Danfoss have incorporated a unique back channel cooling concept within the VSD to ensure up to 90% of the heat losses are removed from the MCC and/or switch-room using the internal heatsink fan within the VSD rather than multiple force vent fans mounted on the doors of the MCC itself.
As an example, Danfoss Drives recent work with a UK based panel builder to integrate a 400kW VSD into their MCC reduced the number of cooling fans required for the MCC from six to only two. As the full project consisted of 4 x 400kW VSD panels this resulted in a total of 16 fans being eliminated from the original design; resulting in reduced material cost, reduced labour cost, reduced running costs, less risk of panel/filter contamination and a significant reduction in acoustic noise. A further benefit of this unique cooling concept is that the Back Channel Cooling fan is controlled by heatsink temperature. The VSD cooling fan will only run when the temperature rises to a switch on level and we have also adapted this cooling fan to be variable speed control, meaning it will also only run to a speed required to remove the associated heat based on the loading of the system. This is an important benefit as it further enhances the efficiency of the system and reduces acoustic noise.