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The objective of this paper is to examine the factors affecting the sizing and positioning of Ground Heat Exchangers (GHEs) in Cyprus. This is achieved through the investigation of the influence of the temperature, thermal conductivity, specific heat and density of the ground as well as pipe diameter on the performance of GHEs using computer software modelling in conjunction with test data. Also, the long term temperature variation of the ground around the boreholes is examined since this affects the positioning of the GHEs. Because of the large number of parameters involved in the design the desired result can be achieved in various ways by considering the specific parameters. The results of the simulations have shown that, generally speaking, the island of Cyprus is suitable for geothermal heat pumps. [ABSTRACT FROM AUTHOR]

Abstract: A Project funded by the Research Promotion Foundation of Cyprus was undertaken by the Cyprus University of Technology and other collaborators, to investigate and determine the geothermal parameters of the ground in Cyprus since such information is currently unavailable. The purpose of this paper is to report on the ground temperatures collected by now, at the six representative sites in relation to depth, time of the year, structure of the ground and altitude and report on their impact on the efficiency of Ground Coupled Heat Pumps. Every month since October 2009, the temperature of the ground is being recorded along the depth of the boreholes. It is anticipated that the project will be completed by the end of 2010 and geothermal information will be collected and reported for all six locations. The data collected until now clearly indicate that there is a potential for the efficient use of GCHPs in Cyprus leading to significant savings in power. [Copyright &y& Elsevier]

The aim of this paper is to show a practical way of estimating the thermal ground properties, namely the ground thermal conductivity, and in particular the thermal diffusivity and the volumetric heat capacity in a reliable manner, for sizing Ground Heat Exchangers (GHEs). A well-known thermal model, proposed by Blackwell in 1954, is applied and is validated both in the heating mode and in the cooling mode, using a GHE as a probe. The value of the thermal conductivity can be easily determined by the model but the procedure also requires knowledge of the ground specific heat capacity and density, which are normally deduced from the (non-accurate) geological data of the site. In addition to the above, the thermal model is also solved analytically –based on the actual parameters used in the experiment–leading to the computation of the ground thermal diffusivity, the volumetric heat capacity and the thermal resistance of the GHE. The possible errors and drawbacks of the whole method are then discussed and finally a complete set of guidelines is provided to the field Engineer for estimating the ground thermal properties from a single test, rendering the use of the geological data of the side unnecessary. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The efficiency of ground-source heat pumps depends on the correct sizing of the associated ground heat exchangers (GHEs). Multiple ground layers with regard to GHE and the presence of more than one loops in each borehole (multiple U-tubes) are sparsely raised in the literature. Therefore the accurate prediction of the performance of the GHE under these conditions is of fundamental importance. A newly developed and validated model is applied to a multiple layer ground regime with different properties and the effect of the layer sequence on the outlet temperature is examined. The model is also modified to allow the study of a double U-tube GHE in a single borehole and the assessment of its efficiency with regard to its building cost. Various configurations are then compared to show that an in-series double GHE is the most efficient. The numerical model developed for energy flows and temperature changes in and around a borehole, when a fluid circulates through single and double U-tubes, is validated upon comparing its results with established experimental results for a single GHE. This model is an improvement of a previous one, based on the time-dependent convection–diffusion equation. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: Earth heat exchangers are essential parts of the ground-source heat pumps and the accurate prediction of their performance is of fundamental importance. This paper presents the development and validation of a numerical model for the simulation of energy flows and temperature changes in and around a borehole heat exchanger when a fluid circulates through a U-tube. Based on the time-dependent convection–diffusion equation, the FlexPDE software package is employed to solve the resulting boundary value problem that model a heat exchanger. First, the mathematical model is validated through a comparison with data obtained from experiments with real borehole set-ups in Cyprus. Then the validated model is used to study the heat flow and the temperature variation in the heat-exchanger. Finally conclusions are extracted on how various parameters like the U-tube diameter, the variation of the ground thermal conductivity and specific heat and the borehole filling material affect the temperature of the inlet and outlet fluid. [Copyright &y& Elsevier]