Results 1 - 9 of 9
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[en] Highlights: • Frosting and heating performance of DX-SAHP under frosting conditions is investigated. • The conditions when DX-SAHP frosts are studied. • The frosting process is observed during 360 min of operating. • The effect of ambient temperature, relative humidity and solar irradiation is analyzed. - Abstract: Direct expansion solar-assisted heat pump system (DX-SAHP) is promising in energy saving applications, but the performance of DX-SAHP under frosting conditions is rarely reported in the published literatures. In this paper, a DX-SAHP system with bare solar collectors for space heating is designed and experimentally investigated in the enthalpy difference lab with a solar simulator. The system is tested under a range of frosting conditions, with the ambient temperatures from 7 °C to −3 °C, the relative humidities of 50%, 70% and 90% and the solar irradiances of 0 W/m"2, 100 W/m"2, 200 W/m"2 and 300 W/m"2. The conditions when the DX-SAHP system frosts are studied. Results show that solar irradiance as low as 100 W/m"2 can totally prevent frosting when the ambient temperature is above −3 °C and the relative humidity is 70%. Besides, the frosting process is observed to be slower than that of fin-and-tube heat exchangers. The evaporator is not seriously frosted and the system performance is not significantly influenced after 360 min of continuous operating. Moreover the effects of ambient parameters, including the ambient temperature and the relative humidity, especially solar irradiation, on the system performance are studied and analyzed. Solar irradiation can effectively prevent or retard frosting, and also improve the heating performance of the DX-SAHP system. The DX-SAHP system is proved to be applicable under frosting conditions.
[en] Highlights: • Models of thermoelectric generator arrays in series and parallel under different heat flux were made. • Models of the thermoelectric generator arrays were experimentally verified. • The number of the thermoelectric generators in array for maximum output power was optimized. - Abstract: The study on thermoelectric generator combined with the solar concentrator has increased rapidly in recent years. However, the solar concentrator inevitably causes the uneven distribution of the heat flux, which would significantly impact the performance of the thermoelectric generator array. This work presented the models of thermoelectric generators in series connection and parallel connection. Furthermore, series of experiments were made to verify the rationality of the model. In addition, the discussion based on the model was conducted to optimize the output power. The results indicated that for the thermoelectric generator array with the large heat flux gradient, which may be more effective and efficient to obtain higher output power through giving up lower heat flux part, which also can reduce the number of the thermoelectric generator modules. This work can be as a hint for the optimization of the solar thermoelectric generator
[en] Highlights: • A design of tri-functional photovoltaic/thermal solar collector is proposed. • The performance of tri-functional PV/T collector is investigated and compared. • The tri-functional PV/T collector is flexible to different working modes and variable seasons. - Abstract: Photovoltaic/thermal (PV/T) solar collectors can provide electric power and thermal energy simultaneously. Either PV/T water collectors or PV/T air collectors can be left unused in some seasons because of the freezing problem of water and seasonal demand of hot air. In this paper, a novel design of tri-functional PV/T solar collector was proposed. The collector can work in PV/water-heating mode or PV/air-heating mode according to the seasonal requirements. Experiments were conducted in different working modes under variable conditions to evaluate the performance of collector. The results show that the daily thermal efficiency achieved 46.0% with the electrical efficiency of 10.2% in PV/air-heating mode. The temperature increase of air reached 20 °C with the flow rate of 0.033 kg/s on a sunny day. The instantaneously thermal efficiency at zero reduced temperature were 37.4% and 44.3% as the air flow rate was 0.026 kg/s and 0.032 kg/s respectively. In PV/water-heating mode, the thermal efficiency of the collector was 56.6% at zero reduced temperature, and the daily thermal efficiency of the system was around 36.0%. Compared with solar collectors presented by other authors, the tri-functional PV/T collector is able to operate efficiently in various conditions
[en] Highlights: • A novel PV-TE system was presented. • Mathematical model of the system was built. • Performance under different ambient conditions was analyzed. • New PV-TE and the conventional PV were compared. • Preliminary economic analysis was demonstrated. - Abstract: Photovoltaic-thermoelectric (PV-TE) hybrid system is one typical electrical production based on the solar wide-band spectral absorption. However the PV-TE system appears to be economically unfeasible owing to the significantly higher cost and lower power output. In order to overcome this disadvantage, a novel PV-TE system based on the flat plate micro-channel heat pipe was proposed in this paper. The mathematic model was built and the performance under different ambient conditions was analyzed. In addition, the annual performance and the preliminary economic analysis of the new PV-TE system was also made to compare to the conventional PV system. The results showed that the new PV-TE has a higher electrical output and economic performance.
[en] Highlights: • A new CAES system for trigeneration based on electrical peak load shifting is proposed. • The theoretical models and the thermodynamics process are established and analyzed. • The relevant parameters influencing its performance have been discussed and optimized. • A novel energy and economic evaluation methods is proposed to evaluate the performance of the system. - Abstract: The compressed air energy storage (CAES) has made great contribution to both electricity and renewable energy. In the pursuit of reduced energy consumption and relieving power utility pressure effectively, a novel trigeneration system based on CAES for cooling, heating and electricity generation by electrical energy peak load shifting is proposed in this paper. The cooling power is generated by the direct expansion of compressed air, and the heating power is recovered in the process of compression and storage. Based on the working principle of the typical CAES, the theoretical analysis of the thermodynamic system models are established and the characteristics of the system are analyzed. A novel method used to evaluate energy and economic performance is proposed. A case study is conducted, and the economic-social and technical feasibility of the proposed system are discussed. The results show that the trigeneration system works efficiently at relatively low pressure, and the efficiency is expected to reach about 76.3% when air is compressed and released by 15 bar. The annual monetary cost saving annually is about 53.9%. Moreover, general considerations about the proposed system are also presented.
[en] Highlights: • A prototype of an ALCPC-PV/T system was designed and set up. • Good optical agreements were observed between simulation and experiment. • The effects of the temperature on the electrical characteristics were discussed. • The thermal performance for circulating cooling was analyzed. • The system efficiency was calculated to present the overall performance. - Abstract: A novel air-gap-lens-walled compound parabolic concentrator incorporated with photovoltaic/thermal system (ALCPC-PV/T) was proposed. The optical, electrical and thermal performances of the ALCPC-PV/T under the outdoor condition were analyzed for building integrated concentrating photovoltaic/thermal application. The simulation and experiment were carried out to reveal the optical characteristics of ALCPC-PV/T on two typical days. The experiment results verified the optical simulation results that the ALCPC-PV/T system had a half acceptance angle of 35° and an average optical efficiency of 83.0% within the half acceptance angle for direct incidence. Furthermore, the average optical efficiencies on the two typical days were all above 60% under the actual outdoor condition considering direct and diffuse solar radiation. Details of electrical characteristics affected by the temperature of circulating cooling water were also displayed. The electrical and thermal efficiencies of the ALCPC-PV/T system during the test were 6.0% and 35.0% respectively with the final water temperature of 70 °C. In addition, the fitted results indicated that under the zero reduced temperature condition, the thermal efficiency of the ALCPC PV/T system was 52.0%, and the corresponding electrical efficiency was 6.6%
[en] Highlights: • A solar thermoelectric with micro-channel heat pipe system was presented. • Mathematical model of the system was built. • Experiment and the simulation were compared to verify the model. • Performance of the system with different factors was analyzed. - Abstract: Micro-channel heat pipe can convert the low heat flux to the high heat flux by changing the ratio of the evaporator area to the condenser area and has a higher heat transfer performance than the common heat pipe. Combining the solar concentrating thermoelectric generation with micro-channel heat pipe can save the quantity of thermoelectric generation and reduce the cost significantly. In this paper, a solar concentrating thermoelectric generator using the micro-channel heat pipe array was designed, and the mathematical model was built. Furthermore, the comparison of the experiment and the simulation between the solar concentrating thermoelectric generator using the micro-channel heat pipe array and the thermoelectric generations in series was made. In addition, the performance on the different areas of selective absorbing coating, different concentration ratios, different ambient temperatures, different wind speed all were analyzed. The outcomes showed the overall performance of the solar concentrating thermoelectric generator using the micro-channel heat pipe array system.
[en] Highlights: • A novel solar thermoelectric cogenerations is studied, designed, realized, characterized, and tested. • The theoretical models and the thermodynamics process are established and analyzed. • The relevant parameters influencing its performance have been discussed and optimized. • The results demonstrated the system is one of the most efficient similar products among either open literature or products. - Abstract: In this paper, a high-performance solar thermoelectric system for combined heat and power is developed and investigated. This new system has achieved a higher performance by considering some of the features, including a simplified structure, lower contact thermal resistance, lower convection heat loss, and better heat transfer performance. The mathematical model was built and analyzed. And the models are verified via the experimental prototype test. In addition, the performance of the system under different environmental conditions and operating parameters are evaluated and predicted. The results show that the proposed system can be used for cogeneration of heat water and electric power. And when the solar irradiation is larger than 700 W/m"2, and water temperature of 13 °C, the maximum instantaneous electrical power output was found to be 0.659 W at the load resistance 4.2 Ω, and the power generation efficiency of the thermoelectric generator (TEG) is 1.956%, which is close to that of a low temperature organic Rankine cycle system. These results indicate the feasibility of the proposed high-performance solar thermoelectric system and give hints for future improvement of the solar thermoelectric system for combined heat and power.
[en] Highlights: • A novel static incorporated CPC-PV/T system was designed and set up. • Theoretical model of optical efficiency under outdoor condition was established. • Experimental evaluation on the optical performance was completed. • Comparing simulation and experiment on typical days was made to assess the system. - Abstract: Optical performance is a significant factor for concentrating photovoltaic/thermal (PV/T) system, especially when the static concentrator is under outdoor condition, which would indicate the preliminary characteristics of the whole system. This paper put forward a novel static incorporated compound parabolic concentrator (CPC) with PV/T system, whose concentrator is composed of the mirror CPC and lens-walled structure, and can make full use of the total internal reflection and specular reflection. The theoretical model on the optical performance of the system under real application condition was established and the outdoor experiment was carried out to compare the simulation evaluation. The results illustrated that the difference on optical efficiency of the simulation and experimental outcome during the test is small, and maximum of it is only approximately 5%. The study obtained the optical efficiency model on the whole day of the static incorporated compound parabolic concentrator and verified the rationality of the design which provided the guarantee for the further research on the building integrated with concentrating photovoltaic/thermal (BICPV/T) system