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SUMMARYThe objective of the work is to investigate the possibility of decreasing the operational energy consumption of the chilled ceiling (CC) and displacement ventilation (DV) hybrid cooling system by sizing the two subsystems to deliver appropriate CC sensible load removal capacity compared to total load and appropriate DV air supply flow rate. A system selection methodology is presented using Ghaddar et al. (ASHRAE Transactions (RP-1438) 2008; 143(2):574-587) design charts to size and generate feasible CC and DV subsystem sizes that meet the desired load and to select the appropriate combination of the system components; chilled panel, cooling coil, and fan. This step is followed by an optimization step of the system transient operation for each of the selected designs to evaluate the corresponding annual energy consumption of optimized operation per selection.The optimized selection methodology was demonstrated in a case study of an office space with known load profile in Beirut climate. It was found that the selection of equipment has a great impact in the operational cost resulting in a difference up to 19% between the various considered selections. An appropriate predictive correlation was derived between the annual energy consumption and the influential design parameters R and P for optimal operation of the CC/DV system.