Figure 15: Using Multiple Fans (Both Operating)
Environmental Guidelines
DVN 5000
24-10520-22 Rev. –
25
This document contains confidential and proprietary information of Johnson Controls, Inc.
© 2009 Johnson Controls, Inc.
Fan Life
Of the many types of fans available, ball-bearing fans outlast sleeve-bearing fans by
about 50%. At 90ºF (32ºC) a ball-bearing fan lasts approximately 55,000 hours,
while a sleeve-bearing fan quickly becomes inoperable at this temperature.
Because of the necessary bearings inside fan assemblies, fans are more susceptible
to failure than any other component. Since fans wear out faster at higher speeds, the
most practical way to extend fan life is to use a proportional speed thermostatic fan
control circuit, which extends equipment life and reduces service calls by varying
fan speed based upon temperature. A temperature probe triggers fans when an
enclosure’s internal temperature reaches a pre-set level.
Variable speed fans are also
self-adaptive
; they take into account changes in ambient
temperature and the varying power dissipated by equipment. Even if you employ
filters, the more unnecessary air that is forced through the rack deposits dust inside
the electronics, reducing its thermal transfer. Slowing the airflow down to the
required amount reduces the deposited dust.