SERRISTE is a decision making system that generates daily climate set points for greenhouse grown tomatoes. The system is based on the mathematical formalisation of expert practices and scientific knowledge, as a constraint satisfaction problem. The structure of SERRISTE is presented, as well as the knowledge used to describe the relationship between the crop behaviour and the greenhouse climate, and the relationship between set points and the resulting greenhouse climate. The performances of the system have been tested in three different locations in France by applying a blind reference management and SERRISTE management to two identical greenhouse compartments at each location. The main results are that SERRISTE maintains higher day to night temperature differences and lower vapour pressure deficit than the reference management, and leads to energy savings in the range of 5–20%. The SERRISTE crop yields at least the same harvest as the reference one. Moreover, the crop behaviour in summer is enhanced by the use of SERRISTE, because the plants are more vegetative and more able to endure high temperatures.