In an organic Rankine cycle (ORC) system, the working fluid pump plays an important role in the system performance. This paper focused on the operating characteristics of a multistage centrifugal pump at various speeds and condensation conditions. The experimental investigation was carried out to assess the influence of the performance of the pump by the ORC system with special attention to actual net power output, thermal efficiency as well as back work ratio (BWR). The results showed that an increase in the pump speed led to an increase in the mass flow rate and expand in the operating range of the outlet pressure. The mass flow rate decreased nonlinearly with the increase of the outlet pressure from 0.22 to 2.41 MPa; the electric power consumption changed between 151.54 and 2409.34 W and the mechanical efficiency of the pump changed from 7.90% to 61.88% when the pump speed varied from 1160 to 2900 r/min. Furthermore, at lower pump specific speed the ORC system achieved higher thermal efficiency, which suggested that an ultra-low specific speed pump was a promising candidate for an ORC system. The results also suggested that the effects of condensation conditions on the pump performance decreased with the pump speed increasing and BWR was relatively sensitive to the condensation conditions, especially at low pump speed.

A new-type multiple-source heat pump cycle with two-stage compression was established on the basis of the problems of similarly existing heat pumps. The equivalent temperature levels of typical evaporators are applied to the different heat sources of the proposed cycle, and the high-temperature heat sources are shown to enhance vapor injection. Then, the mathematical model and prototype are developed, and the results from experimental simulation and validation showed that the solar collector can improve the heating performance of the proposed heat pump system. In the middle-temperature heating period, the outdoor temperature is less than −25°C, and the average coefficient of performance (COP) value of the proposed heat pump was 4.2, which was greater than the COPs of conventional ground source heat pumps.