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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Energy and Buildings, Volume 65, October 2013, Pages 75–83
Utilization of wind and solar energies coupled with heat pumps is a promising technology for energy conservation and emission reduction. This paper describes a rooftop wind solar hybrid heat pump system for building hot water, heating and cooling loads and presents energy and exergy analyses as well as an environmental benefit assessment. The system consists of a shrouded wind-lens turbine subsystem, a flat-plate solar thermal subsystem and a water/air source heat pump subsystem, where the wind and solar subsystems are compactly installed on the rooftop. The solar collector heats water for supplying domestic hot water and increasing the heat pump evaporation temperature for room heating. Heat pumps are used for room heating and cooling and auxiliary heating domestic hot water. Wind power contributes to satisfying the heat pump power demand. Energy and exergy analyses show that the solar thermal subsystem is exergetically inefficient and thus a better design of the solar collector can improve the system exergy efficiency. Wind power can provide 7.6% of the yearly heat pump power demand to satisfy the thermal loads of a 198 m2 residential building in Beijing. The system can yearly reduce 31.3% carbon dioxide emission compared with conventional energy systems.
Renewable energy utilizations for buildings are important ways toward zero energy consumption and zero emission buildings . As common renewable energies, wind and solar energies can be combined for complementary use because wind energy is richer in winter than in summer while solar energy is the opposite. Therefore, wind solar hybrid utilization for building heating and cooling is a promising technology for sustainable development. As another common technology for energy saving, heat pumps can be coupled with renewable energy to improve the system efficiency . Kilkis  theoretically analyzed a wind-geothermal heat pump system which utilized a 6 kW wind turbine to drive a geothermal source heat pump and the results showed that the system could satisfy a 100 m2 residential building heating and cooling loads. Ozgener  and  set up an experimental system of a solar assisted geothermal heat pump together with a 1.5 kW wind turbine for a greenhouse heating load and found that the wind power could supply 3.13% of the heat pump yearly power demand. Chow et al.  designed a solar assisted heat pump system for indoor swimming pool space and water heating, and found that the system coefficient of performance (COP) could reach 4.5 and the energy saving ratio was 79% compared with conventional energy systems. Tagliafico et al.  presented a steady state model of a water-to-water heat pump coupled with flat plate solar collectors for swimming pool water heating in various Italian sites and found that the degree-days index was the main independent variable for the energy saving assessment of the systems. Caglar and Yamali  analyzed a solar assisted heat pump with an evacuated tubular collector for domestic heating and the system COP could reach 6.38. Moreno-Rodriguez et al.  designed a direct-expansion solar assisted heat pump for domestic hot water and the acquired COP could reach 2.9. However, as the reason that the wind turbines used in the existing systems are lowly efficient and occupy much room detached from the building, there are very few studies on the wind power/solar thermal hybrid heat pump system for residential building thermal loads. Further, several researchers analyzed the performance of renewable energy utilization systems using the irreversible thermodynamic theory , , , ,  and . Koroneos and Tsarouhis  assessed independent solar heating, absorption cooling, electric assisted water heater, and photovoltaic systems using exergy and lifecycle assessment theories and concluded that the exergy efficiencies of solar based systems were relatively low and should be improved. Al-Sulaiman et al.  analyzed a solar driven trigeneration system with parabolic through solar collectors and an organic Rankine cycle for cooling, heating and electricity generation and pointed out that the solar collectors and organic Rankine cycle evaporators were the main sources of exergy destructions. This paper describes a rooftop wind solar hybrid heat pump system for residential building hot water, heating and cooling loads and presents energy and exergy analyses as well as an environmental benefit assessment. Firstly, the thermal loads of a two story building in Beijing are simulated for the application of the system. Secondly, the system is described in detail and the energy conservation and exergy balance equations are solved to analyze the system performance according to the meteorological data of Beijing and the building thermal loads. Finally, the environmental benefits are analyzed compared with conventional energy systems.
نتیجه گیری انگلیسی
This paper presented theoretical design and performance analyses of a rooftop wind solar hybrid heat pump system for residential building hot water, heating and cooling loads. The system mainly consists of a wind power subsystem with a highly efficient shrouded wind-lens turbine, a solar thermal subsystem with an 11.4 m2 flat-plate solar collector and a heat pump subsystem with a water source heat pump for room heating and cooling and an air source heat pump as a domestic water auxiliary heater. The solar collector provides domestic hot water and increases the heat pump evaporation temperature. The wind power is used to provide electricity for the heat pumps. The system can operate at the hot-water-only mode, the hot water/heating cogeneration mode and the hot water/cooling cogeneration mode depending on the ambient temperature. The thermodynamic analyses show that the solar collector exergy efficiency (within 0.35–3.6%) is much lower than the other subsystems and can significantly decrease the system efficiency. Therefore, a better design of solar collectors can significantly improve the system exergy efficiency. The parameter dependence study shows that the system exergy efficiency generally decreases with increasing ambient temperatures and solar radiation and may significantly increase with increasing wind speeds if the wind speed is high enough and generates extra wind power for other domestic power demands. The monthly system exergy efficiencies are within 2.4% and 16% for Beijing weather conditions and much higher in winter than in summer. The yearly heat pump COPs for room heating are within 3.6 and 6.7 when the heat pump perfectibility is fixed as 0.2. In this case, the wind power can provide 7.6% of the yearly heat pump power demand. Meanwhile, the environmental benefit analysis shows that the system can yearly reduce 1860 kg carbon dioxide emission with a reduction ratio of 31.3% compared with conventional heating, cooling and hot water production ways in Beijing.