To accelerate the start-up period of Gatton NDDCT, windbreak walls are introduced under the heat exchanger inspired by theoretical analysis, which suggests quicker start-up with increasing values of β, which is a factor that represents the proportion of crosswind redirected into the tower via the heat exchanger by windbreak walls. Three-dimensional (3-D) numerical models at three different wind angles of attack and at crosswind ranging from 1 m/s to 15 m/s produce results consistent with the theoretical analysis. The start-up time with crosswind always follows the similar trend, i.e., first increasing to the peak and decreasing monotonously until a critical speed, beyond which the start-up time keeps almost constant. The air flows through individual heat exchanger bundle due to the interaction between the natural draft (due to heating) and the crosswind effects. These effects are resolved separately at each bundle location at the acting wind speed. Finally, optimum orientations to accelerate the start-up duration are numerically computed. When the wind is mild at up to 4 m/s, windbreak walls are better designed at a 60° wind angle of attack. For crosswind speeds from 5 to 8 m/s, 0° windbreak walls have a better performance. Finally, for wind speeds over 9 m/s, the 30° windbreak walls seem to be most effective. These results should be applicable to any relatively short NDDCT and also imply that at sites with non-uniform wind conditions, a facility to change the windbreak walls orientation with respect to the wind speed would be useful.