M. Petrakis

Comparison of methodologies for tmy generation using 20 years data for Athens, Greece

Abstract The need of accurate Test Reference Years (TRYs) for simulations has been well recognised over the years. Various methods for deriving TRYs have been developed, but their final results can be significantly different. In this paper, the major methodologies reported in literature were applied to 20-year hourly measurements of weather data from Athens, covering the period 1977 to 1996. Seventeen TRYs were produced in total. The basis to select the “best” performing TRY includes meteorological criteria (inherent in the selection process used by each method) and comparisons of results from various simulations for typical energy systems (i.e. a solar water heater, a building, a large scale solar heating system with interseasonal storage and a photovoltaic system). Based on the results of each simulation exercise, a scoring system was developed and applied. The best performing TRY was found to be the one produced by a modified Festa-Ratto method.

Generation of a typical meteorological year for Nicosia, Cyprus

The present study is concerned with the generation of a Typical Meterological Year for Nicosia, Cyprus. The above tool will be useful for the prediction and comparison of the performance and cost effectiveness of passive and active solar systems in the island. The Typical Meteorological Year was generated from available hourly meteorological data recorded during the period 1986–1992, using the Filkenstein-Schafer statistical method.

A software tool for the creation of a typical meteorological year

Abstract The generation of a typical meteorological year is of great importance for passive solar architectural applications. In this context, within the PASCOOL project, a software tool has been developed, utilizing the Filkenstein-Schafer statistical method for the creation of a typical meteorological year. Using this software tool, a typical meteorological year was generated for Athens, Greece. The data used were from the National Observatory of Athens and cover a period of 17 years (1977–1993).

Estimation of the Linke and Unsworth–Monteith turbidity factors in the visible spectrum: application for Athens, Greece

Abstract Expressions for the Linke, TLvis, and Unsworth–Monteith, TUvis, turbidity parameters in the visible region of the solar spectrum are derived. They are based on new determinations of the visible transmittances for the various atmospheric constituents obtained by spectrally integrating the wavelength-dependent atmospheric transmittances. Application of the TLvis and TUvis expressions for Athens is made for the first time; this is done from measurements of direct solar irradiance in the period 1992–1995. A linear interdependence between TLvis and TUvis is derived, as in the case of their broadband counterparts. The seasonal, monthly and daily variations of these turbidity parameters are also investigated.

Modelling the dispersion of a toxic substance at a workplace

The occupational health and safety of the workers in chemical plants are of great importance because they are exposed to concentrations of toxic substances that may exceed institutional limits. This work presents a methodology of assessing the indoor dispersion of the toxic chemical substance Vinyl Chloride Monomer (VCM) in a Polyvinyl Chloride (PVC) chemical plant using Computational Fluid Dynamics (CFD) techniques. A mathematical model using the CFD Code PHOENICS based on solving the full 3-D Navier-Stokes and scalar conservation equations together with turbulence modelling is used to predict the toxic VCM dispersion in a geometrically complex industrial area. The source emissions, as well as the effect of the geometrical details of the building structure were also studied. The results showed that the use of a CFD is a promising technique to study the occupational exposure in the known carcinogen VCM and to design the proper ventilation system to reduce the consequences of an accidental release of VCM in a workplace.

Comparison of performance and cost effectiveness of solar water heaters at different collector tracking modes in Cyprus and Greece

Abstract The present study is concerned with investigation of the thermal performance and cost effectiveness of thermosyphon solar water heaters with different solar collector tracking modes under the weather and socioeconomic conditions of Nicosia–Cyprus and Athens–Greece. The tracking modes are the traditional configuration with the collector surface fixed to 40 degrees from the horizontal, the single-axis tracking with vertical axis, fixed slope and variable azimuth and the seasonal tracking mode where the collector slope is changed twice per year. The investigation is conducted through computer simulations using the trnsys program. The results of the simulations indicate that the traditional thermosyphon solar water heater with fixed collector surface is the most cost-effective configuration as compared to single-axis tracking and seasonal tracking. For Nicosia, the best performance is obtained with the single-axis mode, which results in a yearly solar fraction of 87.6% as compared to 81.6% with the seasonal mode and 79.7% with the fixed surface mode, while the corresponding figures for Athens are 81.4%, 76.2% and 74.4%, respectively. The payback time of this mode, however, is 10–11 years as compared to 5 years with the fixed collector surface tracking mode.

The Effect of Meteorological and Pollution Parameters on the Frequency of Hospital Admissions for Cardiovascular and Respiratory Problems in Athens

This study aimed to investigate the influence of meteorological and pollution parameters on the frequency of hospital admissions for cardiovascular and respiratory diseases. The study included 1,554 patients who were hospitalised in a major hospital in Athens during an 8-year period. The meteorological and pollution database consists of daily values of 12 original parameters and 24 constructed ones. The statistical methods used to analyse it were simple linear correlation and linear stepwise regression analysis and they were applied to 10-day period data. The results showed that temperature, humidity and smoke concentrations were significantly correlated with the incidence of cardiovascular and respiratory diseases.

Relationship of Air Quality Indicators and Synoptic Scale Circulation at 850 hPa over Athens During 1983–1995

The daily relationship between synoptic circulation in the lower troposphere and air quality conditions is demonstrated over the Athens Metropolitan Area (AMA) for the period between 1983 and 1995. This approach utilises eight distinct synoptic categories at the isobaric level of 850 hPa and air quality indicators with respect to O3, NO2, CO, SO2 and black smoke (BS). It is demonstrated that high concentrations of photochemical pollutants and SO2 are closely related to the synoptic scale circulation while CO and BS show a weaker correlation. The most favourable synoptic pattern for the accumulation of high concentrations is the open anticyclonic circulation and for the occurrence of extreme events the closed anticyclone. NO2 and BS present the highest frequency of severe events. The seasonal analysis reveals that the bad and extreme air quality conditions due to O3 and NO2 prevail in the warm season while during the cold season CO and SO2 events prevail. The synoptic category representing a combination of...

Atmospheric stability and atmospheric circulation in Athens, Greece

SummaryIn the evaluation and study of atmospheric pollution reference is always made to the stability criteria. These criteria, usually represented as functions of different meteorological data such as wind speed and direction, temperature, solar radiation, etc., play a very important role in the investigation of different parameters that affect the build up of pollution episodes mainly in urban areas. In this paper an attempt is made to evaluate the atmospheric-stability criteria based on measurements obtained from two locations in and nearby Athens. The atmospheric stability is then examined along with the other meteorological parameters.

A study of frost events in areas characterised by the absence of observations

SummarySerious events of radiative frost were reported in an important agricultural area of central Macedonia, the valley of Lagadas, at the end of March 1994. Since the phenomenon has a strong local character and no surface observations are available, a simulation is performed using a three dimensional numerical model in order to investigate the horizontal and vertical thermal structure of the lower troposphere during the frost event. The synoptic analysis reveals that the background flow was weak, associated with anticyclonic circulation and insignificant pressure gradient in the lower troposphere. Under these synoptic conditions, it was demonstrated that the meteorological model represents successfully the temperature and wind fields over the valley of Lagadas during the frost event. It appears that the model can serve as an alternative method to analyse the characteristics of the radiative frost that occurs very frequently over the examined area associated with substantial economic repercussion.