Experimental Investigation of the Impact of Under Floor Blockages on Flow Distribution in a Data Center Cell

Due to the increase in the rack power of computer equipment, in recent years, thermal management of data centers has become a challenging problem. Data center facilities with raised floor plenums are the most popular configuration from a ducting configuration perspective. The under floor plenum serves as a distribution chamber for the cooling air. Plenums are also used to route piping, conduits and cables that bring power, server network connections, and supply coolant to the air conditioning units. Computational modeling studies have shown that, these under floor blockages impede the flow of cold air from the air conditioning units and yield unpredictable air flow patterns. In this paper, the impact of under floor blockages on flow distribution in a data center is experimentally investigated. A data center experimental cell with one server rack and one air conditioning unit is examined. A number of perforated tiles and their resistances are altered to achieve variable flow patterns under the raised floor. Using previously established guidelines for the placement of under floor structures (piping, etc.) three different scenarios are studied, i.e. no blockages, blockages in critical flow path and blockages in safe flow path are considered. Experiments were carried out for two different tile designs, with free area ratios of 16% and 30%, respectively, and three tile configurations. A detailed comparison between the experimental and CFD model results are presented for several different cases, showing good agreement. Blockages if placed in critical path are shown to significantly reduce the supply tile flow rates which directly affects the thermal performance of the corresponding server. Blockages are shown to have minimal impact when they are placed in safe path. Based on CFD model and experimental results, guidelines on managing under floor blockages are verified. Emphasis has been given to the routing the blockages from safe paths and to keeping critical paths blockage free.