Monthly means of daily solar irradiation over Egypt estimated from satellite database and various empirical formulae

International audienceMonthly means of daily solar irradiation retrieved from the HelioClim-3 version 3 database (HC3v3), elaborated from Meteosat satellite images, were tested at 14 Egyptian stations along with the model of Yang, Koike and Ye (YKY) and 10 empirical models (EMs) for the period 2004 to 2009. YKY and EMs were fitted to measurements from the period 1980 to 1989. Overall, HC3v3 exhibits a bias of 0.4 MJ m 2 (i.e. 2% of the mean of the observations similar to the best EMs). The root mean square error (RMSE) was 1.8 MJ m 2 (9%) for HC3v3 which is lower than for most EMs. Coefficients of determination (R2) were greater than 0.9 for most models. The regression line between estimates and observations exhibits a slope of 1.01 and an intercept of 0.09 MJ m 2 for HC3v3, reflecting a better performance than other models. HC3v3 shows remarkable constant performance as a function of irradiation or cloudiness compared with EMs and YKY. In general, HC3v3 is preferred to EMs when estimating monthly means of daily solar irradiation in Egypt. It is suggested that more effort is needed towards the validation and promotion of HC3v3 before researchers and practitioners use it rather than EMs

Assessing surface solar irradiance in Northern Africa desert climate and its long-term variations from Meteosat images

International audienceTwo databases of solar surface irradiance (SSI) derived from satellites are compared to ground measurements for Algeria, Egypt, Libya and Tunisia. It is found that it is possible to accurately derive the SSI from geostationary meteorological satellites, even with a coarse spatial resolution. The two databases HelioClim-1 and SSE exhibit similar and good performances. The bias is lower for SSE than for HelioClim-1, as a whole; inversely, HelioClim-1exhibits a smaller scattering of data compared to ground measurements (smaller standard-deviation) than the SSE, allowing better performances when mapping the long-term variations in the SSI. These long-term variations from 1985 to 2005 show that these four nations experience dimming as a whole. Detailed analyses of the range of dimming at sites with long-term records and of its spatial distribution have been performed. It has been found that the analysis of SSI from HelioClim-1 supports the findings for the individual sites. Several phenomena may explain the dimming. One is the transportation of sand dust northwards from the Sahel; another one is the increase in urbanization and a third one is the increase in cloud cover and aerosol loading

13th International Heat Transfer Conference IHTC-13

Due to the great awareness of global warming, energy savings should be on the mind of all design engineers. Saving energy in refrigerated vertical display cabinets, which is a major supermarket appliance, is of great importance to users and manufacturers. The aim of this paper is to investigate how to minimize energy usage of refrigerated vertical display cabinets by optimizing the design of its double glazed door. Choosing the gap width can be crucial for optimizing the refrigerator efficiency. The computational fluid dynamics software ‘Fluent’ is used to predict the heat gain through the double glazed door by solving a steady 2-D model for the natural convection in the air gap including heat transfer due to radiation. The air gap investigated is 1.5m high and assumed to have different width 5, 10, 15, 17, 20, 25, 30 & 35 mm which gives aspect ratios in the range 300–43. Results show that as the gap size increases (i.e. aspect ratio decreases) the heat gain due to natural convection decreases up to a limit and then reaches almost a constant value while the radiation heat transfer shows an opposite trend. However, the total heat transfer gain decreases until it reaches a constant value. These results suggest that increasing the gap width improves the door’s efficiency; but only up to a certain limit after which the increase in the gap width does not affect the heat transfer anymore. Results also show that at the small gap width (i.e. high aspect ratio), heat transfer due to convection and radiation is almost equal and as the gap width increases, the radiation component starts to have more dominance. This suggests that the use of a type of glass with lower emittance properties may enhance the thermal effectiveness of the door

Latent Semantic Indexing (LSI) Based Distributed System and Search On Encrypted Data

Latent semantic indexing (LSI) was initially introduced to overcome the issues of synonymy and polysemy of the traditional vector space model (VSM). LSI, however, has challenges of its own, mainly scalability. Despite being introduced in 1990, there are few attempts that provide an efficient solution for LSI, most of the literature is focuses on LSI’s applications rather than improving the original algorithm. In this work we analyze the first framework to provide scalable implementation of LSI and report its performance on the distributed environment of RAAD. The possibility of adopting LSI in the field of searching over encrypted data is also investigated. The importance of that field is stemmed from the need for cloud computing as an effective computing paradigm that provides an affordable access to high computational power. Encryption is usually applied to prevent unauthorized access to the data (the host is assumed to be curious), however this limits accessibility to the data given that search over encryption is yet to catch with the latest techniques adopted by the Information Retrieval (IR) community. In this work we propose a system that uses LSI for indexing and free-query text for retrieving. The results show that the available LSI framework does scale on large datasets, however it had some limitations with respect to factors like dictionary size and memory limit. When replicating the exact settings of the baseline on RAAD, it performed relatively slower. This could be resulted by the fact that RAAD uses a distributed file system or because of network latency. The results also show that the proposed system for applying LSI on encrypted data retrieved documents in the same order as the baseline (unencrypted data)

Validation of the surface downwelling solar irradiance estimates of the HelioClim-3 database in Egypt

International audienceHelioClim-3 (HC3) is a database providing time series of the surface downwelling solar irradiance that are computed from images of the Meteosat satellites. This paper presents the validation results of the hourly global horizontal irradiance (GHI) and direct normal irradiance (DNI), i.e., beam irradiance at normal incidence, of versions four and five of HC3 at seven Egyptian sites. The validation is performed for all-sky conditions, as well as cloud-free conditions. Both versions of HC3 provide similar OPEN ACCESS Remote Sens. 2015, 7 9270 performances whatever the conditions. Another comparison is made with the estimates provided by the McClear database that is restricted to cloud-free conditions. All databases capture well the temporal variability of the GHI in all conditions, McClear being superior for cloud-free cases. In cloud-free conditions for the GHI, the relative root mean square error (RMSE) are fairly similar, ranging from 6% to 15%; both HC3 databases exhibit a smaller bias than McClear. McClear offers an overall better performance for the cloud-free DNI estimates. For all-sky conditions, the relative RMSE for GHI ranges from 10% to 22%, except one station, while, for the DNI, the results are not so good for the two stations with DNI measurements

SEAg 2009: Agricultural Technologies In a Changing Climate

Pigs are subjected to intensive environmental control and management for higher productivity due to their sensitivity to climatic variation. The climate affects pigs’ growth and impacts greatly on the profitability of this industry. The aim of the current work is to numerically model the air velocity and temperature in a free ventilation piggery for grower pigs (32-52 kg) and to investigate the effect of variation in the design on the environment inside the piggery and more specifically at the pigs’ level. These variations were reducing the height of the outer wall of the piggery to the same level as the pens and changing the type of fence used in the pens as well as adding louvers in the air opening, changing the shape of the roof and adding insulation to the roof. A steady twodimensional numerical model based on the integral volume method including the effect of buoyancy, turbulence and heat generated by the pigs was solved using the computational fluid dynamics software Fluent. The results suggest that varying the type of fence from a solid internal fence to one made of separated bars (new fence) did not have much impact on the environment inside the piggery. When this change was combined with the other variation such as lowering the outer walls it made some improvements. Combining the new fence, lowering the outer walls and changing the shape of the roof resulted in the highest increase in the air speed of about 0.2-0.4 m/s at the pigs’ level. These improvements would be only sufficient in milder climate. If these variations were combined with appropriate water sprayers it will help to meet the pigs’ thermal comfort limit at that hot climate