Tunisia has a sunny climate; therefore, the use of solar energy to heat greenhouses can be a solution to reduce the heating cost. A thermal model has been developed to investigate the potential of using a solar water system for greenhouse heating. This system is mainly based on capillary heat exchangers integrated in the greenhouse and ensuring the ground heat storing. A numerical study is conducted using Trnsys16 in order to estimate the exchanger length and the water flow rate allowing the best performance of the system. The inputs of Trnsys16 software were evaluated by experimental tests. The cost and the efficiency of the system were estimated for different greenhouses size. It was concluded that the heating cost of a 1000 m(3) greenhouse was reduced by 51.8% in April and the system can alone satisfy the heating needs for a 10 m3 greenhouse. The good efficiency of the studied system was validated by an experimental study. The simulated and experimental results were compared and error did not exceed 6% which makes Trnsys16 simulation program an efficient tool to reproduce the real behavior of the ground solar water heating system. (C) 2015 Elsevier Ltd. All rights reserved.