At the heart of Mr. Slim P-Series ductless air conditioners and heat pumps lies Variable Compressor Speed Inverter (VCSI) technology. Unlike conventional machines which only cycle between On and Off, VCSI systems detect changes in room temperature and readjust the compressor speed to provide high-speed cooling or heating as needed. This is because the VCSI system operates at partial load for maximum efficiency rather than maximum capacity, thus the system runs more economically than a fixed speed, fixed capacity system. By adjusting the allocated potential capacity to meet the changing demands, the VCSI system uses only the energy needed in any given situation. Most importantly, the bottom line is that your energy costs are reduced.