Papers by Soteris Kalogirou
Energy, 2012
ABSTRACT In this paper a neural network is used for the generation of geothermal maps (contours) ... more ABSTRACT In this paper a neural network is used for the generation of geothermal maps (contours) of temperature at three depths (20, 50 and 100 m) in Cyprus. Archived data of temperature recorded at 41 boreholes is used for training a suitable artificial neural network. The complete data was randomly divided into a training and validation dataset. The neural network is used to predict the temperature at any arbitrary location on the island, which can subsequently be used for drawing geothermal maps. For this purpose, a multiple hidden layer feedforward architecture was chosen after testing a number of architectures. The correlation coefficient obtained between the predicted and training dataset is 0.9889, which is very close to 1, indicating an accurate mapping of the data. The validation of the network was performed using the validation (unknown) dataset. The correlation coefficient for the unknown cases was 0.9253. The prediction error for the temperature was confined to less than 1.74 °C, which is considered quite adequate. In order to broaden the database, the patterns used for the validation of the technique were embedded into the training dataset and a new training of the network was performed. The architecture and the other parameters of the network were kept the same as for the validation phase. The correlation coefficient value for this case was equal to 0.9918. A 10 × 10 km grid is then drawn over a detailed topographic map of Cyprus and the various input parameters were recorded for each grid-point. This information was then supplied to the trained network and by doing so, temperature at the same depths as above was predicted at each grid-point. The x and y coordinates and the estimated temperatures at the three depths for both the original boreholes and at the grid-points were then used as input to a specialized contour drawing software in order to draw the geothermal maps. These maps will be a helpful tool for engineers wanting to apply geothermal heat in Cyprus.
Journal of Thermal Biology, 1999
This paper deals with the thermal analysis of reptiles and pelycosaurs. The energy budgets affect... more This paper deals with the thermal analysis of reptiles and pelycosaurs. The energy budgets affecting the body temperature of the reptile are presented. In the analysis the behaviour of the reptile, energy gains and losses due to metabolism, evaporation, solar heat, convection, and radiation are considered. The effect of the sail of pelycosaurs is also examined. Finite difference equations are
Renewable Energy, 2001
... Designers introduced plans from the west, which were used in industrialised societies. These ... more ... Designers introduced plans from the west, which were used in industrialised societies. These designs have been applied to the Cypriot environment with no changes to fit the social or climatic conditions, losing the comfort offered by the traditional house environment. ...
The objective of this paper is to present an analysis of the weather data contained in a Typical ... more The objective of this paper is to present an analysis of the weather data contained in a Typical Meteorological Year (TMY) and observe the effect of these data on the simulated load of a typical building. The weather data, contained in the TMY, are analysed with ...
ABSTRACT This paper is published in the CLIMA 2000 International Conference, Naples, Italy, 2001.... more ABSTRACT This paper is published in the CLIMA 2000 International Conference, Naples, Italy, 2001. The objective of this work is to use Artificial Neural Networks for the estimation of the daily heating and cooling loads. The daily loads of nine different building structures have been estimated using the TRNSYS program and a typical meteorological year of Cyprus. This set of data has been used to train a neural network. For each day of the year the maximum and minimum loads were obtained from which heating or cooling loads can be determined. All the buildings considered, had the same areas but different structural characteristics. Single and double walls have been considered as well as a number of different roof insulations. A multislab feedforward architecture having 3 hidden slabs has been employed. Each hidden slab comprised of 36 neurons. For the training data set the R2-values obtained were 0.9896 and 0.9918 for the maximum and minimum loads respectively. The method was validated by using actual (modeled) data for one building, for all days of the year, which the network has not seen before. The R2-values obtained in this case are 0.9885 and 0.9905 for the two types of loads respectively. The results indicate that the proposed method can be used for the required predictions for buildings of different constructions. At present the method was used primarily to investigate its suitability for this kind of predictions.
Sustainable Development and Planning IV, 2009
… , 2000. MELECON 2000. …, 2000
... Comparison of the periodic solution method with TRNSYS and SUNCODE for thermal building simul... more ... Comparison of the periodic solution method with TRNSYS and SUNCODE for thermal building simulation, Solar Energy, Vol. ... Michaelides IM, Kalogirou SA, Roditis G., Chrysis I. and Hadjigianni A. (1998), “Generation of a ''Typical Meteorological Year” for Nicosia, Cyprus”, ...
Renewable Energy, 2013
... Vassilios Messaritis a ,; Ioannis Panayides b ,; Zomenia Zomeni b ,; George Partasides c ,; A... more ... Vassilios Messaritis a ,; Ioannis Panayides b ,; Zomenia Zomeni b ,; George Partasides c ,; Andreas Lizides c ,; Eleni Sophocleous d ,; Kostas Koutsoumpas e. ... The refrigerant has the ability to change state, from liquid to gas when heated and usually it boils at low temperatures. ...
ABSTRACT Photovoltaic (PV) materials are increasingly being incorporated into the construction of... more ABSTRACT Photovoltaic (PV) materials are increasingly being incorporated into the construction of new buildings for generating electrical power and are used to replace conventional building materials in parts of the building envelope such as the roof, skylights, or facades. Also photovoltaic systems may be retro it - integrated into existing buildings. The advantage of integrated photovoltaic systems over the non-integrated systems is that their initial cost can be offset by reducing the cost of the materials and labo r that would normally be spent to construct the part of the building that is replaced. This study examines the effect of air flow on a building integrated PV-panel. It is shown that in summer, the maximum temperature of a PV-panel of 3 m in height is experienced for an east facing surface and reaches 77 °C early in the mornin. The maximum temperature for a south facing panel is 51 °C and that for a west fac ng surface is 58 °C. The air velocity in the air-gap between the PV-panel and the building wall is an important factor. It is shown that for an air-gap width of 0.02 m, an air velocity of 0.5 m s–1 can lower the mean temperature of the panel from 77 °C to 39 °C, allowing for a significant increase in its efficiency. Finally the air-gap width is varied for a steady elocity of 0.2 m s–1, and it is shown that the temperature of the building wall varies from 23.7 °C for a width of 0.01 m to 20 °C for a width of 0.05 m.
Energy, 2013
ABSTRACT This paper describes the mathematical modeling of vertical and horizontal GHEs (ground h... more ABSTRACT This paper describes the mathematical modeling of vertical and horizontal GHEs (ground heat exchangers) and compares their efficiency. The model used calculates the heat flow in the fluid, tubes, grout and ground. The vertical U-tube GHE is represented by two 100 m lines, embedded in four different types of ground with an additional bottom base. The horizontal GHE consists of four 50 m tube lines embedded in three ground layers. The initial ground temperature for all cases examined matches real data acquired in June at a location in Cyprus and the simulation results for the vertical GHE are validated using measured data showing very good agreement. Further simulations with the vertical GHE show that when the initial ground temperature rises, the mean temperature of the GHE fluid increases proportionally. Comparisons between horizontal and vertical GHEs reveal that under the same operating conditions and center-to-center distances of the tubes, the vertical GHE keeps a much lower mean temperature. Simulations for a horizontal GHE, for a 50-h of continuous operation period and 24 °C initial ground temperature, show that the mean fluid temperature can remain lower than that of the vertical GHE if the center-to-center distance of the tubes increases to 1 m.
Renewable Energy, 2015
ABSTRACT In this paper a neural network is used for the generation of a contour map of the ground... more ABSTRACT In this paper a neural network is used for the generation of a contour map of the ground conductivity in Cyprus. Archived data of thermal conductivity of ground recorded at 41 boreholes are used for training a multiple hidden layer neural network with feedforward architecture. The correlation coefficient obtained between the predicted and training data set is 0.9657, indicating an accurate mapping of the data. The validation of the network was performed using an unknown dataset. The correlation coefficient for the unknown cases was 0.9553. In order to broaden the database, the patterns used for the validation of the technique were embedded into the training data set and a new training of the network was performed. The correlation coefficient value for this case was equal to 0.9718. A 10 × 10 km grid is then drawn over a detailed topographic map of Cyprus and the various input parameters were recorded for each grid point. This information was then supplied to the trained network and by doing so ground conductivity was predicted at each grid-point. This map will be a helpful tool for engineers in designing geothermal heat pump systems in Cyprus.
Renewable & Sustainable Energy Reviews, 2002
The objective of this paper is to examine solar cooling and low energy cooling technologies. A br... more The objective of this paper is to examine solar cooling and low energy cooling technologies. A brief review of various cooling systems is presented, including solar sorption cooling, solarmechanical systems, solar related air conditioning, and other low energy cooling technologies. The relative efficiencies and applications of the various technologies are presented. These technologies can be utilized to reduce both the energy consumption and environmental impact of mechanical cooling systems.
The temperature distribution in the ground is distinguished in three zones. The Surface zone, whi... more The temperature distribution in the ground is distinguished in three zones. The Surface zone, which reaches a depth of about 1m, the Shallow zone extending at a maximum depth of 20 m, and the Deep zone, where the ground temperature remains nearly constant throughout the year. To effectively exploit the heat capacity of the soil a heat-exchanger system has to be constructed. Usually an array of buried pipes running along the length of the building, a nearby field or buried vertically into the ground is utilised. A circulating fluid (water or air) is used in summer to extract heat from the hot environment of the building and dump it into the ground and vice versa in winter. A heat pump may also be coupled to the ground heat exchanger to increase its efficiency. In the literature several calculation models are found for ground heat exchangers. One-dimensional models were devised in the first stages of the system study which were replaced by twodimensional models during the nineties and three-dimensional systems during the recent years.
Applied Thermal Engineering, 2002
In this paper the modelling, simulation and total equivalent warming impact (TEWI) of a domestic-... more In this paper the modelling, simulation and total equivalent warming impact (TEWI) of a domestic-size absorption solar cooling system is presented. The system consists of a solar collector, storage tank, a boiler and a LiBr-water absorption refrigerator. Experimentally determined heat and mass transfer coefficients were employed in the design and costing of an 11 kW cooling capacity solar driven absorption cooling machine which, from simulations, was found to have sufficient capacity to satisfy the cooling needs of a well insulated domestic dwelling. The system is modelled with the TRNSYS simulation program using appropriate equations predicting the performance of the unit. The final optimum system consists of 15 m 2 compound parabolic collector tilted at 30°from horizontal and 600 l hot water storage tank. The total life cycle cost of a complete system, comprising the collector and the absorption unit, for a lifetime of 20 years will be of the order of C£ 13,380. The cost of the absorption system alone was determined to be C£ 4800. Economic analysis has shown that for such a system to be economically competitive compared to conventional cooling systems its capital cost should be below C£ 2000. The system however has a lower TEWI being 1.2 times smaller compared to conventional cooling systems. Ó
Solar Energy, 2008
The objective of this work is to present the development of an automatic solar water heater (SWH)... more The objective of this work is to present the development of an automatic solar water heater (SWH) fault diagnosis system (FDS). The FDS system consists of a prediction module, a residual calculator and the diagnosis module. A data acquisition system measures the ...
Applied Thermal Engineering, 2008
A ground heat exchanger can be used for the injection or extraction of thermal energy into/from t... more A ground heat exchanger can be used for the injection or extraction of thermal energy into/from the ground. The line source model is an easy method of evaluating the characteristics of the borehole and does not need expensive equipment. This method is presented and a test is performed in order to determine a borehole's characteristics in layers consisting of clay, silt and sand at various analogies. For the borehole under test the ground thermal conductivity (k) was found to be 1.605 W/(m K) and the effective borehole thermal resistance (R b ) to be 0.257 K/(W/m). The accuracy of the collected data could be affected mainly by two factors. The first factor is the daily flux penetration through the ground which gradually increases the temperature of the top layers and the second factor is a variation of the heating coil injection rate per active length of borehole. As it was observed this combined effect has a negligible result on the mean fluid temperature during the test hours of 280-400, when the system was operating at steady state.
Energy and Buildings, 2010
ABSTRACT The significance of the residential building sector in terms of energy consumption is we... more ABSTRACT The significance of the residential building sector in terms of energy consumption is well acknowledged. In this view the knowledge of the way the residential building stock of Cyprus behaves in terms of energy consumption is quite valuable since it will assist policy makers to formulate targeted measures aiming the improvement of energy efficiency and setting current legal standards and benchmarks in the energy performance certificate, a requirement of the 2002/91/EC Directive. Unfortunately, the existing knowledge on this subject is quite poor. As a remedy a research project supported by a national research grant is in operation since December 2008. This paper presents the outline, goals and methodology of this research project and the findings regarding the energy behaviour and other characteristics of the residential building stock of Cyprus. From the analysis of the results for 500 residential buildings, it seems that the energy demand and primary energy required is lower than that of other European countries. Moreover, it seems that the age of residential buildings has low correlation with the energy demand while in contrast with other Northern and Central European countries, it is clear that the contribution of cooling energy requirements to the overall energy demand is quite significant.
Applied Energy, 2002
... TRNSYS runs through hourly values of various weather parameters included in a typical meteoro... more ... TRNSYS runs through hourly values of various weather parameters included in a typical meteorological year (TMY) file. The TMY for Nicosia, Cyprus, developed by Petrakis et al. ... 62.2 P, ventilation and acceptable indoor-air quality in low-rise residential buildings, specifies the ...
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Papers by Soteris Kalogirou