Systems and methods for selectively cooling heat-generating electronic components in an enclosure. According to one embodiment, an enclosure houses a plurality of heat-generating electronic components. Air enters the enclosure at the front and is exhausted at the rear. After passing through one or more upstream components, air diverges into at least first and second airstreams within the enclosure. The first airstream is re-cooled by a cooling system having a thermoelectric cooling module. The thermoelectric cooling module is configured such that a first side is cooled and a second side is heated in response to an applied voltage. A voltage regulator may govern the voltage in response to one or more temperatures sensed within the rack system.