Energy-saving system and energy-saving control method

The invention provides an energy-saving system used for a plant factory, and an energy-saving control method. The energy-saving system comprises a heat exchanger, a first feeding device, a second feeding device, an electricity generating unit and a cultivating region. The first feeding device provides a heat exchange medium into the heat exchanger. The second feeding device provides liquid carbon dioxide into the heat exchanger. The liquid carbon dioxide is converted into gaseous carbon dioxide through after flowing through the heat exchanger. The electricity generating unit is connected to the heat exchanger, and comprises a turbine motor and an electricity generator. The gaseous carbon dioxide drives the turbine motor to generate kinetic energy to the electricity generator, and furthermore, electric energy is generated. The gaseous carbon dioxide is transported into the cultivating region after passing through the electricity generating unit, and supplied to plants in the cultivating region for photosynthes