Evaluation of different radiation and albedo models for the prediction of solar radiation incident on tilted surfaces, for four european locations

The diffuse radiation incident on an inclined surface is composed of both the sky diffuse radiation and the ground-reflected radiation. Depending on the model used to calculate the sky diffuse radiation and the estimated albedo value, it is possible to introduce a significant error in the prediction of the total radiation incident on a tilted surface. Twelve sky diffuse submodels associated with four different albedo submodels are used to estimate the total radiation on the tilted surface from data on the horizontal plane. The predicted total solar radiation values are compared with measured data on a south facing vertical surface, from four representative south and north European locations. Root mean square error, mean bias error, and a t-test are used to determine the intrinsic performance of each combination of diffuse tilt and albedo submodel. Accordingly, the various model combinations do not exhibit a statistically significant difference between measured and calculated values. © 1996 by ASME

High ambient air temperature frequency distribution at Hellenic islands

Energy consumption of buildings for cooling purposes partially depends on outdoor ambient air temperatures. Measured data from eight Hellenic islands in the Ionian and the Aegean sea is used to estimate the frequency of high temperature exceedance in these islands, useful for estimates of building cooling demand and comfort conditions in the area. The analysis is based on the calculation of the daily TE value, which is the sum of the daily minimum outdoor temperature and half of the daily temperature amplitude. This parameter corresponds to a daily average value of 9-10 h, during the period of May through September, when the hourly ambient temperature exceeds 26 and/or 28°C in the regions of interest. The analysis carried out shows that a two-parameter exponential law, is in excellent agreement with the large values distribution for the parameter TE. © 1998 Elsevier Science S.A. All rights reserved

Calculation of ground albedo for the estimation of global radiation on tilted surfaces, for four European locations

Ground albedo can influence the estimation of solar radiation incident on tilted surfaces. Depending on the model used to calculate the sky diffuse radiation and the estimated albedo value, it is possible to introduce a significant error in the prediction of global radiation on a titled surface. In this paper, several methods for calculating ground albedo values, used for estimating the global radiation on a tilted surface, are proposed and evaluated. The predicted global solar radiation values are compared with measured data on a south facing vertical surface, from four representative south and north European locations. It appears that there is a significant impact on the accuracy of calculating the global solar radiation incident on a tilted surface using different methods for calculating ground albedo values

Passive solar agricultural greenhouses: A worldwide classification and evaluation of technologies and systems used for heating purposes

Results from a recently completed study of 95 solar greenhouses from around the world, representing the state-of-the-art in this field, are presented and are classified. Relevant technical information on the utilised heating systems using alternative energy sources are identified and the existing applications are grouped according to the characteristics of the implemented type of technology. Five categories of passive solar greenhouses are reviewed, according to the characteristics of the heat storage system, namely, water, latent heat material, rock bed, buried pipes, and some other type of systems. Available information on the performance of each system is also included. The suitability of the technologies for each climatic zone and type of cultivation is estimated and evaluated. This up-to-date information on the state of the art in this field can be of great importance to potential users for the successful development of future applications. © 1994

Natural convection heat transfer coefficients from vertical and horizontal surfaces for building applications

Correlations for natural convection heat transfer coefficients from experimental studies are reviewed and compared for their applicability to real surfaces in buildings. All correlations have been modified for appropriate Prandtl and Grashof numbers in building applications. A comparative statistical analysis reveals that there is a good agreement between the available correlations. © 1994