In order to increase the quality and quantity of agricultural products from greenhouse cultivation, and to cope with a very competitive market, it is necessary to have an optimal climate inside the greenhouse. To achieve this, the farmer uses expensive and very power-consuming heating and cooling systems. In order to solve this problem, a new system has been developed with a solar thermal collector and a specific heat transfer fluid. The experimental study of this new system has shown that this new system was able to keep the temperature inside the greenhouse in an optimal range for the development of the plants.