Random noise can generate a unidirectional heat current across asymmetric nano-objects in the absence (or against) a temperature gradient. We present a minimal model for a molecular-level stochastic heat pump that may operate arbitrarily close to the Carnot efficiency. The model consists a fluctuating molecular unit coupled to two solids characterized by distinct phonon spectral properties. Hea...

A simulation model for the CO2 heat pump water heater was developed and validated in this study. Component models of the gas cooler, evaporator, compressor, and expansion valve were constructed with careful consideration for the heat transfer performances. To validate the simulation model, experiments were carried out using an actual CO2 heat pump water heater (water heating capacity: 22.3 kW; ...

In this study the integration of an absorption heat pump (AHP) with the concentration section of an industrial pulp and paper process is investigated using pinch technology. The optimum design of the proposed water-lithium bromide AHP is then achieved by minimizing the total annual cost. A comprehensive optimization is carried out by relaxation of all stream pressure drops as well as heat excha...

The performance of the two types of vapor-injection (VI) cycles in a heat pump system is compared. The vaporinjection cycle using an internal heat exchanger (IHX) has a choice to select the branching point of the injection stream. The two VI cycles are different in terms of branching points of the injection stream. Different branching points of the injection stream influence the heating capacit...

Centrifugal heat pump has to be coupled with gas boiler to supply high temperature water in radiator heating system. Regarding to hybrid heating system (HHS), operation strategy has significant impact on its annual energy consumption and cost. In this paper, the optimal operation strategy of the HHS composed of sewage-source centrifugal heat pumps and gas boilers was analyzed. Firstly, the perf...

With the increasing of the environmental concerns, carbon dioxide (CO2) as an alternative refrigerant has been investigated intensively. In this study, the heating performance of a transcritical CO2 heat pump system with a twinrotary compressor was investigated. The transcritical CO2 heat pump with gas injection was tested by varying gas injection ratio and outdoor temperature at the optimum re...