The Persian or Sistan wind mill is possibly the oldest wind energy device. It consists of a vertical axis with six blades, and an outer shroud which encases half the rotor against the wind. The wind only acts on one half of the runner, providing the driving force. The efficiency of this machine was assumed to be between 5 and 14%, too low for practical application today. The concept however is interesting since it has the potential for integration into buildings. Recently, the Sistan wind mill was re-visited to assess whether the performance could be improved. Initial exploratory tests reported in the literature indicated potential. At Southampton University, a series of tests was conducted with a model of 0.6 m diameter and 0.5 m high runner employing an improved measurement and data acquisition system. Two geometries were investigated. Qualitative tests indicated that a gap between blade and axis is essential for functionality. Performance tests with an improved geometry resulted in efficiencies of 0.4-0.5, similar to e.g. Darrieus-type VAWTs, for blade to wind speed ratios of 0.82-1.8. The modified resistance-type vertical axis wind turbine appears to have potential for further development. (C) 2017 Elsevier Ltd. All rights reserved.