Abstract : This paper introduces the energy-saving principle of variable frequency speed control and its energy-saving renovation scheme in central air conditioning systems. Keywords: Variable frequency speed control; Central air conditioning system; Energy-saving renovation 1 Variable Frequency Drive and Energy Saving In agricultural production and daily life, it is often necessary to control some physical quantities, such as the temperature of air conditioning systems, the water pressure of water supply systems, and the air volume of ventilation systems. Most of these systems are driven by AC induction motors. Previously, because the speed of the motors could not be easily adjusted, people had to use simple methods to control these physical quantities, such as using baffles to adjust the air volume and valves to adjust the flow rate. This resulted in these systems not only failing to achieve good regulation effects, but also wasting a large amount of electrical energy. Statistics show that the power consumption of fan and pump loads accounts for a considerable proportion of China's total power generation. Currently, about 25% of the energy used by fans and pumps in China is wasted. Therefore, energy-saving renovation of fans and pumps has great potential. Based on the characteristics of AC induction motors, the best way to achieve continuous and smooth speed regulation is to use a variable frequency drive (VFD). A VFD converts standard AC power into AC power with variable frequency and voltage, supplying it to the motor and regulating its speed. Using VFDs for energy-saving retrofits of fans and pumps not only avoids energy waste caused by using baffles or valves, but also greatly improves control and regulation precision. We can easily implement constant temperature air conditioning systems and constant pressure water supply systems. [b][align=center]For more details, please click: Energy-Saving Retrofit Application of VFDs in Central Air Conditioning Systems[/align][/b]