The paper discusses some key design elements about air source heat pump(ASHP) air-conditioning, heating and domestic hot water system for residential uses. The design of ASHP air-conditioning system should focus more on energy-saving, also emphasize air distribution and humidity control to ensure good indoor comfort for a whole year; ASHP domestic water heater should be designed in good consideration on the adaptability of the control strategy under the local climate condition, and the design for a condensi...