Natural draft direct dry cooling system (NDDDCS) uses the natural draft dry-cooling tower instead of axial flow fans, so can effectively reduce the power consumption, operating costs and also the noise caused by fans. In this work, two types of NDDDCS with horizontally arranged heat exchanger bundles (HAHEBs) and vertically arranged heat exchanger bundles (VAHEBs) are proposed respectively. Furthermore, the cooling delta apex angles from 60 degrees to 180 degrees are further investigated. The air-side velocity, pressure and temperature fields are presented and the heat rejections for various configurations of NDDDCS are calculated and compared. The results show that the cooling performance of NDDDCS with VAHEBs is superior to that with HAHEBs in any case, especially at high wind speeds. The VAHEBs with the apex angle of 150 degrees have the best cooling performance, so can be recommended in the potential practical engineering of natural draft direct dry cooling system in power plants. (C) 2017 Elsevier Ltd. All rights reserved.