A novel fin-tube collector/evaporator was used in a direct expansion solar assisted heat pump(DX-SAHP)water heater.The test rig was tested and several optimization schemes were proposed.The temperature of the collector is usually lower than ambient temperature

which means the collector can absorb heat not only from the solar radiation but also from the environment

so the collector efficiency is high.This novel collector has a bigger heat exchanger area compared with the same-sized roll-board collector.Experimental results show that the average COP of the DX-SAHP water heater can reach 5.37 when the temperature of 150-liter water is increased from 20℃ to 50℃ on sunny days in autumn.And the average COP can reach 3.43 even if on a rainy day with 18.6℃ average ambient temperature.A numerical model of the test rig was established and some optimization schemes for the collector were proposed.The computer simulation results show that the average COP of the DX-SAHP system can reach 6 when the temperature of 150L water is increased from 20℃ to 50℃ on sunny days after the optimization.