In this study an attempt is made to investigate the impact of the urban heat island (UHI) effect on the energy consumption of a building using both, an accurate, extensively validated, transient simulation model and a neural network one. The energy consumption is calculated for a typical building during the summer period at 20 different sites of the Greater Athens area with the aid of the TRNSYS model. It was found that the UHI affects significantly the thermal behaviour of the building, implying much lower cooling load cost and energy cost in the suburban areas. A neural network model was then appropriately designed and tested for the estimation of the energy consumption, employing as an input, the UHI intensity. The results of both methods were tested and compared and it was found that there is a good agreement between the cooling rate values calculated by the TRNSYS programme and those derived by the neural model. Moreover, the employment of the neural model helped in quantifying the contribution of each input parameter in the calculation of the cooling rate, and it was demonstrated that the UHI effect is a predominant parameter, affecting considerably the energy consumption of a building in the Mediterranean region. © 2006 Elsevier Ltd. All rights reserved.

A statistical downscaling technique based on artificial neural network (ANN) was employed for the estimation of local changes on seasonal (winter, spring) precipitation and raindays for selected stations over Greece. Empirical transfer functions were derived between large-scale predictors from the NCEP/NCAR reanalysis and local rainfall parameters. Two sets of predictors were used: (1) the circulation-based 500 hPa and (2) its combination along with surface specific humidity and raw precipitation data (nonconventional predictor). The simulated time series were evaluated against observational data and the downscaling model was found efficient in generating winter and spring precipitation and raindays. The temporal evolution of the estimated variables was well captured, for both seasons. Generally, the use of the nonconventional predictors are attributed to the improvement of the simulated results. Subsequently, the present day and future changes on precipitation conditions were examined using large-scale data from the atmospheric general circulation model HadAM3P to the statistical model. The downscaled climate change signal for both precipitation and raindays, partly for winter and especially for spring, is similar to the signal from the HadAM3P direct ouput: a decrease of the parameters is predicted over the study area. However, the amplitude of the changes was different. Copyright © 2006 Royal Meteorological Society.

In this study, an attempt is made to investigate possible teleconnection patterns of atmospheric circulation, centered over eastern Mediterranean (EM) with the aid of gridded NCEP/NCAR daily values of geopotential heights for the period 1958-2003. For this purpose, two approaches have been used: correlation analysis and rotated principal component analysis (PCA) on a seasonal and monthly basis. A teleconnection pattern between the EM and northeastern Atlantic was identified at 500 and 300 hPa in winter, which will be referred to as the Eastern Mediterranean Pattern (EMP), appearing as an independent mode of the upper circulation. The pattern also exists in autumn but is substantially weakened with its dipole centers being shifted eastwards. Significant monthly variations were found in the location, strength and structure of the pattern. The employment of a standardized index demonstrated that the negative phase of the EMP prevails throughout the year with the maximum frequency at wintertime. Copyright © 2006 Royal Meteorological Society.

The purpose of this work is to assess, both experimentally and theoretically the status of air quality in a dentistry clinic of the Athens University Dentistry Faculty with respect to chemical pollutants and identify the indoor sources associated with dental activities. Total VOCs, CO2, PM10, PM2.5, NOx and SO2 were measured over a period of approximately three months in a selected dentistry clinic. High pollution levels during the operation hours regarding CO2, total VOCs and Particulate Matter were found, while in the non-working periods lower levels were recorded. On the contrary, NOx and SO2 remained at low levels for the whole experimental period. These conditions were associated with the number of occupants, the nature of the dental clinical procedures, the materials used and the ventilation schemes, which lead to high concentrations, far above the limits that are set by international organizations and concern human exposure. The indoor environmental conditions were investigated using the Computational Fluid Dynamics (CFD) model PHOENICS for inert gases simulation. The results revealed diagonal temperature stratification and low air velocities leading to pollution stratification, accompanied by accumulation of inert gaseous species in certain areas of the room. Different schemes of natural ventilation were also applied in order to examine their effect on the indoor comfort conditions for the occupants, in terms of air renewal and double cross ventilation was found to be most effective. The relative contribution of the indoor sources, which are mainly associated with indoor activities, was assessed by application of the Multi Chamber Indoor Air Quality Model (MIAQ) to the experimental data. It was found that deposition onto indoor surfaces is an important removal mechanism while a great amount of particulate matter emitted in the Clinic burdened severely the indoor air quality. The natural ventilation of the room seemed to reduce the levels of the fine particles. The emission rates for the fine and coarse particulates were found to be almost equal, while the coarse particles were found susceptible to deposition onto indoor surfaces. © 2007 Elsevier B.V. All rights reserved.

In the present study, an attempt is made to assess the atmospheric boundary-layer (ABL) depth over an urban area, as derived from different ABL schemes employed by the mesoscale model MM5. Furthermore, the relationship of the mixing height, as depicted by the measurements, to the calculated ABL depth or other features of the ABL structure, is also examined. In particular, the diurnal evolution of ABL depth is examined over the greater Athens area, employing four different ABL schemes plus a modified version, whereby urban features are considered. Measurements for two selected days, when convective conditions prevailed and a strong sea-breeze cell developed, were used for comparison. It was found that the calculated eddy viscosity profile seems to better indicate the mixing height in both cases, where either a deep convective boundary layer develops, or a more confined internal boundary layer is formed. For the urban scheme, the incorporation of both anthropogenic and storage heat release provides promising results for urban applications. © Springer Science+Business Media, B.V. 2007.