Further to a previous experimental study on the heat exchanger circuitry number for a two-way discharge active chilled beam terminal unit, an investigation of the tube connecting sequences is conducted in this paper. Given a typical air side operating condition, in situ air velocity profile across the heat exchanger is measured and non-uniformities of the air flow caused by the entrainment effect are detected. Taking the air maldistribution into consideration, heat transfer performance of the heat exchanger is simulated with a tube to tube distributed parameter model. This simulation model is calibrated with experimental results. With the calibrated model, influences of the air maldistribution on the heat transfer capacity are discovered. The heat exchanger tube connecting sequences are optimized through a particle swarm optimization program for the maximum heat transfer capacity. In addition, the potential pressure drop, manufacture difficulties, and material cost of the tube connecting sequences are qualitatively analyzed. A new heat exchanger circuitry arrangement is finally proposed for the terminal unit. Although the performance enhancement is modest, the findings obtained in the study are expected to facilitate better heat exchanger designs for the future active chilled beam terminal units. (C) 2015 Elsevier B.V. All rights reserved.