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research-article  
Rabindra Pokhrel, Luis Ortiz, Nazario Ramirez and Jorge Gonzalez
J. Sol. Energy Eng   doi: 10.1115/1.4041401
The main objective of this study is to identify how climate variability and urbanization influence human comfort levels in tropical-coastal urban environments. San Juan Metropolitan Area of the island of Puerto Rico was chosen as a reference point. A new human discomfort index (HDI) based on environmental enthalpy is defined to determine the energy required to maintain indoor human comfort levels. Regression analysis shows that both temperature and HDI are good indictors to predict total electrical energy consumption. Results showed that over the past 35 years the average environmental enthalpy have increased, resulting in the increase of average HDI. Local scale weather station data show a decreasing rate of maximum cooling per capita at -11.41 kW-h/years, and increasing of minimum cooling per capita of 10.64 kW-h/years, however for the whole Caribbean region an increasing trend for both minimum and maximum cooling per capita is observed. To estimate human comfort levels under extreme heat conditions, an event of 2014 was identified. The analysis is complemented by simulations from the Weather Forecasting System (WRF) at a resolution of 1 km, forced by data from the National Center for Environmental Prediction at 250 km spatial resolution. WRF model results were evaluated against observations showing good agreement for both temperature and relative humidity and improvements. WRF results evidenced that Energy Per Capita in urban areas is larger in extreme heat events than in normal days or in non-urban areas by as much as 30%.
TOPICS: Cities, Climate, Shorelines, Cooling, Heat, Temperature, Resolution (Optics), Enthalpy, Regression analysis, Weather forecasting, Engineering simulation, Energy consumption, Simulation
research-article  
Oscar A. Lopez-Nunez, J. Arturo Alfaro-Ayala, José de Jesús Ramírez-Minguela, J. Nicolás Flores-Balderas and Juan Manuel Belman Flores
J. Sol. Energy Eng   doi: 10.1115/1.4041402
A solar radiation model is applied to a low temperature water-in-glass evacuated tubes solar collector to predict its performance via CFD numerical simulations. This approach allows obtaining the transmitted, reflected and the absorbed solar radiation flux and the solar heat flux on the surface of the evacuated tubes according to the geographical location, the date and the hour of a day. Different environmental and operational conditions were used to obtain the outlet temperature of the solar collector; these results were validated against four experimental tests; based on an Official Mexican Standard resulting in relative errors between 0.8 and 2.6%. Once the model is validated, two cases for the solar collector were studied, i) different mass flow rate under a constant solar radiation and ii) different solar radiation (due to the hour of the day) under a constant mass flow rate to predict its performance and efficiency. For the first case, it was found that the outlet temperature decreases as the mass flow rate increases reaching a steady value for a mass flow rate of 0.1 kg/s (6 l/min), while for the second case, the results showed a corresponding outlet temperature behavior to the solar radiation intensity reaching to a maximum temperature of 36.5 °C at 14:00 hrs. The CFD numerical study using a solar radiation model is more realistic than the previous reported works leading to overcome a gap in the knowledge of the low temperature evacuated tube solar collectors.
TOPICS: Solar radiation, Low temperature, Solar collectors, Flow (Dynamics), Temperature, Computational fluid dynamics, Glass, Computer simulation, Errors, Solar heating, Water
research-article  
Fifi Elwekeel, Antar Abdala and Muhammad Rahman
J. Sol. Energy Eng   doi: 10.1115/1.4041403
The effects of collector roughness shape on the performance of solar chimney power plant were investigated in this study. The roughness shapes of triangular, curved, and square grooves were chosen and were compared to smooth case. The performance parameters of solar radiation, updraft velocity, temperature distribution, static pressure, power, and Nusselt number were varied. The effects of number, position, height and width of the grooves on the performance were investigated. The results of this investigation show that the updraft velocity with the triangular groove increases by 1.5 times compared to the smooth case at solar radiation of 1000W/m2. At solar radiation of 1000 W/m2, the power increases by 169%, 96 % and 19% for triangular, curved, and square grooves, respectively compared to the smooth case. Moreover, the Nusselt number values with triangular groove and curved groove enhances by 42% and 26% respectively compared to the smooth case. The power increases by 1.98% for three grooves instead of using one groove at higher solar radiation. Increasing the groove height by 1.7 times, the power increases by 1.03 times at higher solar radiation. The power enhancement shows less sensitivity to the change of groove width at the higher solar radiation.
TOPICS: Power stations, Solar energy, Roofs, Solar radiation, Surface roughness, Shapes, Temperature distribution, Pressure
research-article  
Miloud Bessafi, Vishwamitra Oree, Abdel Anwar Hossen Khoodaruth, Guillaume Jumaux, Francois Bonnardot, Patrick Jeanty, Mathieu Delsaut, Jean-Pierre Chabriat, Muhammad Zaid Dauhoo and Li Peng
J. Sol. Energy Eng   doi: 10.1115/1.4041404
An accurate assessment of the amount solar radiation incident at specific locations is highly intricate due to the dependence of available solar radiation on many meteorological and topographic parameters. Reunion Island, a small tropical French territory, intends to deploy solar energy technologies rapidly. In this context, the variability and intermittency of solar irradiance in different regions of the island is of immediate interest if the generated energy must be integrated in the existing energy network. This paper identifies distinct features of spatial and temporal variability of daily global horizontal radiation observed on Reunion Island. For this purpose, trends in the mean daily as well as seasonal variability of solar radiation were investigated. Finally, the intermittency and multifractal behaviors of the spatial daily solar radiation change were examined. Results revealed that the difference in cumulative solar radiation for two successive days range between -10 and 10 kW/m2 while the highest and lowest variability of daily change occurs during summer and winter respectively. Moreover, the average decorrelation distance for day-to-day solar radiation change is found to be about 22 km. The Hurst exponent, fractal co-dimension and Lévy parameter, which describe solar radiation intermittency, were also evaluated for Reunion Island.
TOPICS: Solar radiation, Radiation (Physics), Dimensions, Solar energy, Fractals, Meteorology
Review Article  
Abdul Ahad Iqbal and Ali Al-Alili
J. Sol. Energy Eng   doi: 10.1115/1.4041159
The demand for air conditioning and refrigeration has been increasing due to a rise in the global temperature and the burgeoning world population. Conventional electricity driven vapor compression cycles use refrigerants which are harmful to the environment, and are responsible for the consumption of huge amounts of electricity leading to high CO2 emissions. Therefore, solar driven cooling cycles have great potential to address these issues, and the Middle East and North Africa (MENA) region has an abundant supply of solar radiation. In this study, the research carried out within the MENA region on solar cooling technologies is presented. The solar cooling cycles reviewed are the adsorption, absorption, solid desiccant, liquid desiccant, ejector, and solar electric driven cycles. The interest over time and across countries in each of these cycles is also discussed. This review shows that interest in solar cooling technologies has increased sharply in the MENA region since late 2000's, and there are several issues like subsidized electricity prices hindering their adoption. In addition, this work shows researches where more investigations are needed.
TOPICS: Cooling, Solar energy, Cycles, Refrigerants, Emissions, Carbon dioxide, Compression, Vapors, Solar radiation, Air conditioning, Absorption, Ejectors, Refrigeration, Temperature
research-article  
Mustafa Jaradat, Daniel Fleig, Klaus Vajen and Ulrike Jordan
J. Sol. Energy Eng   doi: 10.1115/1.4040841
A solar-assisted liquid desiccant demonstration plant was built and experimentally evaluated. Humidity of the air, density of the desiccant and all relevant mass flows and temperatures were measured at each inlet and outlet position. Adiabatic dehumidification experiments were performed in different seasons of the year under various ambient air conditions. The moisture removal rate m ?_v, the mass balance factor ?_m, and the absorber effectiveness, e_abs, were evaluated. An aqueous solution of LiCl was used as liquid desiccant with an initial mass fraction of about 0.4 kgLiCl/kgsol. The mass flow rate of the air was about 1100 kg/h. The experimental results showed a reduction in the air humidity ratio in the range of 1.3 to 4.3 g/kg accompanied with an increase in the air temperature in the range of 3 to 8.5 K, depending on the inlet and operating conditions. A maximum mass fraction spread of 5.7 % points due to dilution in the desiccant and a volumetric energy storage capacity of 430 MJ/m3 were achieved for an air to desiccant mass flow ratio of 82. By operating the desiccant pump in an intermittent mode, a mass fraction spread of about 13 % points and an energy storage capacity of about 900 MJ/m3 were reached. In addition, the experimental results were compared with results from a numerical model. The numerical model overestimates the heat and mass transfer because it assumes ideal surface wetting and uniform distribution of the circulated fluids.
TOPICS: Solar energy, Dehumidifiers, Flow (Dynamics), Temperature, Computer simulation, Energy storage, Pumps, Dehumidification, Wetting, Mass transfer, Fluids, Heat, Density

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