Search

Shallow Geothermal Energy, a Renewable Energy Source, finds through Ground Heat Exchangers (GHEs) of various configurations (mainly vertical U-tubes, but also horizontal or spiral) that extract or reject heat from / into the ground. The sizing and consequently the cost of such systems (GHEs in conjunction with Ground Source Heat Pumps – GSHPs) depend on various factors. The objective here is to examine the factors affecting the sizing and positioning of GHEs in the Mediterranean environment of Cyprus. There is indeed a large number of parameters involved in the design of such systems, and the desired result can be achieved in various ways depending on the considered parameters. This is done through simulations by commercial design software programs (e.g. GLD) in combination with test data. The parametric study investigates the influence on the performance of GHEs of: (a) the temperature, (b) thermal conductivity, specific heat and density of the ground, (c) pipe diameter (of the GHE). Another important factor studied is the long-term temperature variation of the ground around the GHE boreholes, which affects the positioning of the GHEs. The main outcome of the parametric analysis is that – generally speaking – Cyprus constitutes a proper environment for the application of GSHP/GHE systems. The performance of the GSHP is not affected by the ambient conditions as the ground temperature remains unchanged.

In this paper a neural network is used for the construction of a contour map. The particular case of the thermal conductivity map of the ground of the island of Cyprus is considered, with archived data at a number of boreholes throughout Cyprus being used for training a suitable artificial neural network. The data were randomly divided into a training and a validation dataset for a multiple hidden layer feed-forward architecture. The correlation coefficient obtained between the predicted and the training dataset is 0.966, indicating an accurate mapping of the data, while the validation (unknown) dataset exhibits an also satisfactory correlation coefficient of 0.955. The dataset was broadened by embedding the patterns used for the validation into the training dataset with the correlation coefficient equalling a higher 0.972. The available input parameters were then recorded for each grid point on a detailed topographic map of Cyprus, whereby the neural network was used to predict the thermal conductivity at each point. The coordinates and the estimated conductivity were then used as input to a specialized contour drawing software in order to draw the geothermal contour map.

This paper presents a way of calculating the in-situ borehole ground thermal properties. For this procedure a U-tube ground heat exchanger embedded in a borehole is utilized, allowing hot water to circulate in the tube. The water is heated with constant power and its temperature is recorded in constant time intervals. Then the results are analyzed using the line source method. The formulas are solved using a simple excel program to derive the values of the thermal properties with a fitting technique. These results are compared with measured values of samples taken from the same area where the borehole is located. The comparison shows that only the experimental results analyzed with the theoretical model can give reliable values because the data concern the actual stage of compaction and moisture content of the soil.

Ground-source heat pumps achieve higher efficiencies than conventional air-source heat pumps because they exchange heat with the ground that is cooler in summer and hotter in winter than the air environment. 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 through an incompressible fluid flow, for the simulation of energy and temperature changes in and around a U-tube borehole heat exchanger. The FlexPDE software is used to solve the resulting simultaneous equations that model the heat exchanger. The validated model (through a comparison with experimental data) is then used to extract conclusions 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 fluid., {"references":["H. S. Carslaw and J. C. Jaeger, Conduction of heat in solids, Claremore\nPress, Oxford, 1946.","V. C. Mei and C. J. Emerson, \"New approach for analysis of groundcoil\ndesign for applied heat pump systems,\" ASHRAE Transactions\n91(2B), 1985, pp. 1216-1224.","J. D. Deerman and S. P. Kavanaugh, \"Simulation of vertical U-tube\nground coupled heat pump systems using the cylindrical heat source\nsolution,\" ASHRAE Transactions 97(1), 1991, pp. 287-295.","C. Yavuzturk, J. D. Spitler and S.J. Rees, \"A Transient two-dimensional\nfinite volume model for the simulation of vertical U-tube ground heat\nexchangers,\" ASHRAE Transactions 105(2), 1999, pp. 465-474.","Y. Nam, R. Ookaa and S. Hwanga, \"Development of a numerical model\nto predict heat exchange rates for a ground-source heat pump system,\"\nEnergy and Buildings 40(12), 2008, pp. 2133-2140.","P. Cui, H. Yang and Z. Fang, \"Numerical analysis and experimental\nvalidation of heat transfer in ground heat exchangers in alternative\noperation modes,\" Energy and Buildings 40(6), 2008, pp. 1060-1066.","L. Schiavi, \"3D Simulation of the Thermal Response Test in a U-tube\nBorehole Heat Exchanger,\" in Proc. COMSOL Conference, Milan,\n2009. On line: http://cds.comsol.com/access/dl/papers/6825/Schiavi.pdf","J. C. Heinrich and D. W. Pepper, Intermediate finite element method:\nFluid flow and heat transfer applications, Taylor & Francis,\nPhiladelphia, PA, 1999.","G. Florides and S. Kalogirou, \"First in situ determination of the thermal\nperformance of a U-pipe borehole heat exchanger in Cyprus,\" Applied\nThermal Engineering 28(2-3), 2008, pp. 157-163."]}

The development and validation of a numerical model for the simulation of energy flows and temperature changes in a U-tube borehole heat exchanger is presented. The FlexPDE software package is employed to solve the time-dependent convection-diffusion equation that models the resulting boundary value problem. The model is validated with experimental data and is used to study how various parameters like the U-tube diameter, the ground thermal conductivity and specific heat, affect the exchanger temperature.

The Energy Service of the Ministry of Commerce, Industry and Tourism has the overall responsibility for Energy matters in Cyprus and specifically for preparing and implementing programmes for energy conservation, the promotion of renewable energy sources (RES) and the development of technologies for the utilization of RES. The Government of Cyprus being aware of the benefits of geothermal energy and in order to increase the share of energy from renewable sources consumed in heating and cooling in 2020, promotes the geothermal energy systems through a Scheme that provides financial incentives for the utilization of RES for heating and cooling. However, the lack of valid data for the ground thermal properties in Cyprus was one of the main obstacles for the design of efficient geothermal systems, the implementation of the Schemes in the field of geothermal energy and the calculation of the share of energy from renewable sources for heating and cooling according to the methodology defined by the E.U in the directive 2009/28/EC. In an effort to identify suitable energy efficient systems for heating and cooling of buildings and the correct calculations of their contribution to the national targets, the Energy Service participated in a project founded by the Research Promotion Foundation of Cyprus to investigate and determine the geothermal parameters of the ground of Cyprus at six representative sites in Cyprus, for use in the design of ground heat exchanger applications and ground thermal storage. The paper presents the importance of the Isothermal map that helps consultants to design efficiently geothermal energy systems, calculate effectively heat losses of buildings to the ground and design the thermal energy storage equipment. The importance’s of the results are analyzed by national authorities’ experts’ point of view for evaluating geothermal applications bridging in this way the gap between technical output and commercial reality.

The purpose of this study is to record and compare the ground temperatures and other thermal characteristics of the ground at eight representative sites in Cyprus with other studies both in the island and the nearby Mediterranean countries. Paul Morgan in the 1970s measured the geothermal gradient in 33 boreholes in Cyprus. Since then, the thermal behaviour of the ground has not been sufficiently studied and recorded, especially in inhabited areas, resulting in limited information for the design of ground heat exchangers and its effect on the efficiency of Ground Coupled Heat Pumps (GCHPs). As simulation studies indicate the ground temperature is one of the main system parameters that affect the performance of GCHPs. Measurements carried out on the representative locations in Cyprus show that the surface zone reaches a depth of 0.5m. The shallow zone penetrates to 7-8 m and there after the deep zone follows. Also the temperature of the ground at the deep zone has a range between 18-23 °C and is usually higher than that of the ambient air during the cold months of the year and lower during the warm months, showing suitable temperatures for the efficient use of GCHPs. Ground temperatures in Cyprus are lower than those examined in Jordan and higher than the ones in Portugal.

It is a fact that today in Cyprus there are no building-regulations concerning thermal insulation of the building envelope and consequently no restriction exist regarding energy performance. After joining the EU in May 2004, Cyprus has to comply with various directives of the Union. One of them is the Directive on the Energy Performance of Buildings 2002/91/EC. In order to comply with this requirement, a special committee was formed for the development of the required methodology and software to be used for this purpose. The objective of this paper is to present the methodology and program developed and its characteristics together with the type of output the user is expected to get. Considering that Cyprus is fully dependant on imported energy, it is believed that this new directive will lead to energy efficient buildings, and in the long run it will benefit the economy of the island.