Renewable Energy Research Group @ CUT

https://doi.org/10.1007/s12053-025-10307-3

Abstract

This paper presents the configuration and performance of a Low Enthalpy Geothermal System successfully installed and utilized in the Mediterranean climate zone. Additionally, it examines the performance of different types of Ground Heat Exchangers (GHE), all installed in the same System. The Ground Source Heat Pump (GSHP) of the system consists of vertical ground heat exchangers (GHEs) in five different configurations, one double helicoidal coil in a well and an open loop (well) system. The entire system is constantly monitored by a Building Management System (BMS) that records the energy, volume flow, incoming and outgoing temperature at critical points of the system. Based on the recorded values, the performance of the System was analyzed in a heating and a cooling working mode, after examining the power flows in and out from critical points of the System. Results show higher heat exchange values inside the open well, both in heating and cooling mode suggesting the usage of this type of GHE, where applicable. Additionally, the electric power consumed by the chillers which are the largest electricity consumers within the System, is approximately five times lower than the power placed in the building by the Geothermal System (SCOP between 4.5 and 5). In terms of primary energy savings, we can say with confidence the GSHP systems working under Mediterranean climate zone conditions, can be consider as high efficiency solutions, verifying the theoretical efficiency given by the manufacturer of the GSHP.

https://doi.org/10.1016/j.renene.2024.120835

Ground Source Heat Pumps, in the framework of Shallow Geothermal Energy Systems, outperform conventional Heating Ventilation and Air Conditioning systems, even the high efficiency Air Source Heat Pumps. At the same time, though, they require considerably higher installation costs. The utilization of dwellings’ foundations as ground heat exchanger components has recently demonstrated the potential to generate significant cost reductions primarily attributed to the reduction in expenses associated with drilling and backfill material (grout). These elements are referred to in the literature as Thermo-Active Structures or Energy Geo-structures (EGs). The current study employs a ‘mixed studies’ review (i.e., literature review, critical review and state-of-the-art review) methodology to comprehensively examine and assess the compatibility and integration of different renewable energy sources and environmentally friendly technologies with foundation elements deployed as EGs. These mainly include heat pumps, district heating and cooling networks, solar-thermal systems, waste heat, biomass and other types such as urban structures. Emphasis has been given on the advancement on this area, with the current study identifying and addressing two primary categories. The first category involves the integration of EG elements with sources that are able to supply green electricity, referring to renewable energy electricity obtained from on-grid or off-grid integration. The second category, involves a direct or indirect integration with sources that provide heat, or vice versa. The technical and non-technical barriers of such integrations have been discussed in detail, with the technical challenges generally involving engineering design, and system optimization, whereas non-technical challenges encompassing the economic, social, and policy domains.

Abstract

https://doi.org/10.3390/en17184621

Abstract:

Geothermal systems face adoption challenges due to their high initial investment cost. Accurate cost analyses and a more precise understanding of updated prices could assist geothermal industry projects in obtaining investment financing and better money management with the right equipment. As the cost of geothermal installations can vary widely depending on case and location, it seems essential to clarify the factors and parameters that determine the cost of the system. These include the type of loop system, the ground conditions, the type of heat pump, the system size, and the geographical location. The scope of this study is to compare the operation of various types of ground heat exchangers (GHEs) present in a Ground Source Heat Pump (GSHP) system installed in the coastal area of the Mediterranean climate zone of Cyprus. The highlight of this work is that it presents real installation cost data as well as recorded total energy contributed by the GHEs to the GSHP system of a HP cooling and heating capacities of 101 kW and 117 kW, respectively. The input contribution from the GHEs to the HP is 85,650 kWh (308,340 MJ) in summer and 25,880 kWh (93,168 MJ) in winter. It is shown that, among the three groups of GHEs investigated, the open-well GHE complex has the lowest cost per kWh ratio (0.32 EUR/kWh), followed by the vertical GHE complex (1.05 EUR/kWh), and lastly by the helical coil GHE (2.77 EUR/kWh). This clearly suggests that when underground water is available, the open-well GHE is much more favorable than other GHE types.

Keywords: ground source heat pump; ground heat exchanger; open well; helicoidal coil

https://doi.org/10.5194/egusphere-egu24-8009, 2024

Conference: EGU24 Vienna, Austria, 14-19 April 2024

Authors: Lazaros Aresti, Christos Makarounas, Paul Christodoulides

Abstract: Following the European Union (EU) targets towards the “Fit for 55”, the heat pump (HP) sales have seen an increase. The recent increasing demand in the utilization of HP towards space heating and cooling, underscores the pivotal role of Shallow Geothermal Energy (SGE) systems and the Ground Source Heat Pumps (GSHPs). Although GSHPs exhibit higher performance compared to Air Source Heat Pumps (ASHPs), the high initial cost and the consequent long payback period has been a preventive factor for the GSHP systems. The GSHP systems however also benefit for additional CO2 reduction. The evolving efficiency of ASHP systems in recent studies challenge the perceived advantages associated with GSHPs, particularly in light of the continual refinement of ASHP systems.This research embarks upon a comprehensive analysis to compare the environmental impacts, in terms of CO2 emissions, between ASHP and GSHP systems using different case studies. High insulation profile case studies were considered, following the nearly Zero Energy Buildings (nZEB) technical characteristics, as well as retrofitting at older dwellings with a low insulation profile. The current study engages a Life Cycle Analysis (LCA) with the OpenLCA software in conjunction with the Ecoinvent database, and the employment of the ReCipe impact method, both from a midpoint and an endpoint perspective. The findings derived from this investigation demonstrates a favorable performance of the GSHP systems where there is an increasing demanding in heating such as in the retrofitting cases. This research highlights the important environmental implications of employing the GSHPs over the use of ASHPs.

Abstract

https://hdl.handle.net/20.500.14279/33500

Conference: Sixth International Conference on Computational Methods for Energy and Thermal Problems (THERMAECOMP2024), 9-11 September, Budva, Montenegro

Authors: Paul Christodoulides, Andreas Skaliontas, Lazaros Aresti, Georgios A Florides

Abstract: GSHP systems, a form of shallow geothermal energy system, are used for heating and cooling usuing Ground Heat Exchangers (GHEs) that extract/reject heat from/to the ground. In such systems, the thermal response is represented by the temperature change within the GHE and the surrounding earth as a function of heat extraction or injection. There exist several mathematical models, both analytical and numerical, in the literature that govern the thermal response of GHEs. All such models are based on Fourier’s law, which allows the determination of heat flow due to conduction. Regarding numerical models, they are obviously more accurate than analytical models and can represent the GHE in greater detail. However, numerical models may be too time-consuming for building energy simulations and consequently of limited use in practical applications. In such case analytical models can play a crucial role. Analytical models can be used as alternatives to one another, depending on the case and the accuracy required to solve a problem. Some of these will be applied to an existing case study of a vertical GHE in the Mediterranean island of Cyprus and be compared to the experimental data and conclusions will be derived regarding the accuracy and suitability of each.

https://hdl.handle.net/20.500.14279/33501

Conference: Sixth International Conference on Computational Methods for Energy and Thermal Problems (THERMAECOMP2024), 9-11 September, Budva, Montenegro

Authors: Lazaros Aresti, Georgios A Florides, Paul Christodoulides

Abstract: Shallow geothermal energy is a type of Renewable Energy, used in dwellings through the employment of Ground Source Heat Pumps (GSHPs). GSHPs are coupled with the Ground Heat Exchangers (GHEs), which are responsible for the heat transfer to/ from the ground. GSHPs have not seen a major advancement in terms of wide implementation, as compared to other Renewable Energy Systems, due to the higher costs associated with them. However, the use of the foundation elements as GHEs, can contribute in a significant reduction of the costs and investment. This study computationally investigates the use of an Energy Geo-Structure (EG) system, namely the foundation slab, of a residential dwelling in Cyprus, using the COMSOL Multiphysics software. A single-family house was designed in accordance with the typical Cyprus construction elements for nearly Zero Energy Building (nZEB) characteristics. Initially, the heating and cooling loads were estimated and used as inputs to analyse the performance of the proposed system. The system under examination demonstrates steady performance and relative high Coefficient of Performance (COP) values, making it a viable renewable energy source solution for building integration.

https://hdl.handle.net/20.500.14279/33486

Conference: SIAM Conference on Mathematics of Planet Earth (MPE24), 2024, 10-12 June, Portland, Oregon

Authors: Paul Christodoulides, Lazaros Aresti, Christakis Christou, Iosifina I Stylianou, Georgios A Florides

Abstract: European Union (EU) has developed energy strategies and has invested in new energy technologies to ensure higher energy efficiency of buildings. The Ground Source Heat Pump (GSHP) system is one of the most well-known geothermal systems and renewable energy technologies for heating and cooling of buildings due to its high efficiency (see Coefficient of Performance – COP) and its environmental friendliness. GSHPs make use of Ground Heat Exchangers (GHEs), which are designed to cover the energy demand both in summer and winter. Such geothermal systems can be controlled by a remote monitoring system (building management systems – BMS). In this study the evaluation of a GSHP/GHE system performance regarding the use for heating and cooling in the building where the University Municipal Library of Limassol (Cyprus) is housed. The system (GSHP controlled by the BMS) acts as a research and educational laboratory. The GSHP system includes vertical GHEs with various specifications and two open loop (well) systems. A theoretical and experimental investigation is needed to evaluate the performance of the different parts of the geothermal system and give recommendations for improving its efficiency. The entire GHE system is constantly monitored by a digital program that records the energy, flow, volume, incoming and outgoing temperature at each installed HP. The general three-dimensional convection-diffusion equation is used to model the individual GHEs. In addition, based on data collected for several summer and winter months, (i) the electrical power into the system, (ii) the power absorbed /rejected by/to the system, and (iii) the COP of the whole system (including all installed GHEs) are estimated and compared. By studying the obtained results, several suggestions regarding the operation and the optimization of the GSHP as well as the BMS systems will be discussed.