User`s guide

14 NovaScale 4020 User’s Guide
The figure below shows the cooling subsystem layout with the airflow direction indicated.
Figure 14. Cooling Subsystem Layout
The server system supports only a fully populated system fan configuration. However, the
system will continue to meet thermal specifications with either a system fan or a power supply
failure. The power supply redundancy feature applies to systems with three power modules
installed.
If a fan fails, system cooling is maintained and the system continues to operate while the failed
fan is being hot-swapped. All system fans have tachometer output, internal speed control, and
external Pulse Width Modulation (PWM) speed control.
A failure is detected when the RPM of a fan falls below a predetermined minimum threshold
(Approx. 5000 RPM). If a system fan falls below this threshold, all fans will be boosted to
operate at a higher speed (Approx. 8500 RPM)
The fans will also be boosted to the higher speed if a power supply fails for any reason
(including loss of AC power). The fans will not be boosted if the Redundant (ACR) power
supply fails. If the redundant power supply fails, the system fans will not be affected.
When boosted, all fans remain at high speed until the failed fan or power supply is replaced.
When a fan replacement is detected by a change in state of the fan presence signal. After a
failed fan is replaced, the fans return to the lower speed and fan failure monitoring at the lower
speed levels is reactivated.
When a power supply fails and is replaced, the replacement is detected by server management.