Abstract: In the present study, a heat pump dryer was designed and manufactured, its refrigerant was R22.The performance of opening air cycle, semi-opening air cycle and closed air cycle configurations was studied. When the heat pump works with the opening air cycle, the heat pump unit works in the steady state and extraction water from the process air is lower than that with the semi-opening air cycle. When the heat pump works with the semi-opening air cycle, the extraction water from the process air will increase by exhausted air loss. In the closed system, the bypass air rate(BAR) plays a significant role in the system performance. As BAR increases, the amount of air passing the evaporator is reduced and the BAR directly alters the HPD performance. The extraction water from the process was not sensitive to BAR values within the range from 0.4 to 0.7. To obtain the peak of SMER, the system should be operated with BAR between 0.4 and 0.6. With BAR greater than 0.6, the peak values seem to be reduced. It was, therefore, concluded that the bypassing air rate(BAR) was effective at the maximum SMER.