Passive cooling systems are energy efficient and eco-friendly alternatives to mechanical cooling systems. In this paper, the cooling tower-based thermally activated building system, which acts as an indirect evaporative cooling system, has been investigated using a computational fluid dynamics tool for the hot semi-arid climate of New Delhi. Three design parameters namely spacing, vertical position and arrangement of pipes embedded in the roof and floor were analysed for their influence on the cooling performance of the system. The results indicate that reducing pipe spacing from 0.3 to 0.1 m and moving the pipes closer to the inner surface from 0.135 to 0.015 m could reduce the operative temperatures by 1.6 and 2.7℃, respectively. For the same total water flow rate, a change in pipe arrangement from serpentine to parallel showed insignificant influence on the indoor comfort indices. The best combination of these three parameters can achieve an average operative temperature of 29℃, which is comfortable for the hot semi-arid climate of New Delhi where the adaptive neutral temperature was found to be 29.4℃. This study will contribute to heating, ventilating, air-conditioning designers’ understanding of the importance of these parameters for achieving the required comfort in buildings in India. © 2016, © The Author(s) 2016.