The concept of HVAC includes heating, ventilation, and air conditioning, so it has a broader concept than central air conditioning. The concept of energy saving in HVAC is not to reduce the environment or suppress energy demand in exchange for energy saving, but to improve the energy efficiency of buildings through the application of integrated resource planning (IRP) methods and energy demand side management (DSM) techniques, with limited Resources and minimum energy consumption costs to obtain maximum social and economic efficiency to meet the growing environmental needs. D71 inverter has been widely used in heating, ventilation and air-conditioning systems in high-end places such as airports, radio and television buildings, hospitals, and subways.