Transient Thermal Analysis of an Air-Conditioned IT Rack with a Thermal Buffering Unit

A single, sealed, stand-alone rack is sometimes utilized for commercial and industrial IT deployments. One cooling option is to mount an AC unit at the bottom of the rack which draws in the warm IT exhaust air and supplies cool air to the IT inlets. Mismatches in airflow rate and IT/cooling power lead to recirculations and cycling of the AC compressor creating periodic temperature variations. One solution is to add a "thermal buffering unit" between the AC unit and IT equipment to separate IT and AC airstreams and dampen temperature variations by virtue of its thermal mass. This paper details the thermal analysis of such rack configurations utilizing flow network and compact thermal mass models. The goals of the paper are to introduce the thermal buffering unit concept and illustrate the use of compact thermal-mass models to predict transient temperature variations.