Experiments have been performed on the thermal behavior of a PCM (phase change material) - Trombe wall system with heat transfer enhancement by DWVGs (delta winglet vortex generators). PCM (CaCl2 center dot 6H(2)O) slabs were attached on the gap - side wall surface to increase the heat storage. Delta winglet VG pairs (attack angle beta = 45 degrees, ratio of length to height l/h = 2) were arranged on the surface of PCM panel to enhance the air side convective heat transfer in the gap. The VG height, pitch and locations were also evaluated. The results showed that the delta winglet VG pairs really enhanced the heat transfer rate at the surface of PCM panel during both the charging and discharging processes. Accordingly, the gap air flow rate and heating rate to the room with a single row of delta winglet VG pairs are 28.5% and 39.4% higher than the case without VGs. Delta winglet VG pairs with height of 30 mm, front edge pitch of 2 mm, lateral spacing of 225 mm and vertical spacing of 340 mm give best thermal performance under present conditions. The results indicate the advantages of using longitudinal vortex generators to improve the performance of PCM - Trombe wall systems for passive solar heating. (C) 2015 Elsevier Ltd. All rights reserved.