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Based on a well-designed collector/evaporator, a novel direct expansion solar assisted heat pump water heater is introduced.The device can work by four modes according to solar and ambient temperature conditions (solar energy heating mode by heat pipe principle, heat pump heating mode, defrosting mode, snow removing mode).Performance of the device is analyzed in four seasons with heating percentage by solar energy from 0.3 to 0.9 and ambient air temperature from-10℃ to 40℃.It shows that the average COP of the device is about 20% to 100% higher than that of electric assisted solar energy or air source heat pump water heaters, and the device can achieve satisfactory performance in both north and south areas.