Search Results (17)

This study presents an innovative hybrid geothermal air conditioning system that combines conventional air-based heat exchange with ground heat exchange technology. The system features a ground heat exchanger placed downstream from the outdoor unit heat exchanger, requiring minimal modifications to conventional air conditioners through the addition of bypass flow paths and a four-way valve. This design ensures that the ground heat exchanger consistently operates after the outdoor unit heat exchanger in both cooling and heating modes. The researchers evaluated the proposed system’s performance through both computational simulation (1D-CAE) and experimental testing. Simulation results demonstrated significant efficiency improvements, with the hybrid system achieving a coefficient of performance (COP) of 4.51 compared to just 1.24 for conventional air conditioners under extreme temperature conditions (38 °C). The experimental validation with a shallow-buried (20 cm) ground heat exchanger confirmed an approximately 20% COP improvement across various ambient temperatures. The main advantages of this hybrid system over conventional geothermal systems include reduced installation costs due to shorter borehole lengths, separate air conditioning units and underground piping, and compatibility with existing control systems. The design addresses skilled labor shortages while enabling large-scale demonstration operations with minimal initial investment. Future work will focus on optimizing the burial depth and conducting long-term durability testing to advance practical implementation. Full article

Mid-deep geothermal heat pump systems (MD-GHPs) feature high energy efficiency and low energy consumption, yet their promotion is restricted by high initial investment. While the initial investment of air-source heat pumps (ASHPs) is obviously lower, it also has a larger energy consumption. To address the complementary strengths and weaknesses of single-source heat pump systems, this paper puts forward an integrated system combining MD-GHPs and ASHPs, and the series mode was determined as the optimal integration approach for the hybrid system through comparative analysis. Simulation analysis was conducted to explore the adaptability of series mode, and numbers of mid-deep ground heat exchangers in nine cities across various climate regions were studied. The MD-GHP system is suitable for space heating in Xining and Xi’an, while ASHPs are suitable for space heating in Nanjing and Hangzhou. For intermediate resource areas like Urumqi and Tsingdao, the series mode achieves the best economic benefits during the 24th year of operation. Full article

The global challenges of rising energy consumption and carbon emissions underscore the urgent need for efficient and sustainable heating solutions in the building sector. The implementation of high-performance buildings that envelope insulation and the increasing adoption of low-temperature radiant heating systems have significantly reduced the water temperature required from heat sources, enabling greater compatibility with renewable energy systems. In this study, we propose a renewable energy heating system incorporating a solar-assisted medium-depth ground heat exchanger (MDGHE). A dynamic simulation model of the solar-assisted MDGHE system was developed in TRNSYS, featuring a novel MDGHE module specifically developed to improve simulation accuracy. A case study of a residential building in China was conducted to evaluate the performance of the proposed system. The simulation results demonstrate that while the standalone MDGHE covers 71.9% of the building’s heating demand, integrating solar collectors with the MDGHE can increase this coverage to 99.9%, enabling full compliance with heating requirements without relying on conventional heat pumps. The results revealed that the system’s COP reached 9.26. Compared with the traditional medium-depth ground source heat pump system with the COP of 4.84, the energy efficiency of this system has been enhanced by 47.7%. A static payback period of 7 years has been obtained compared with the cost of central heating service for residential buildings. These findings highlight the potential of solar-geothermal hybrid systems as a sustainable alternative to traditional heating methods. Full article

Geothermal energy has emerged as a cornerstone in renewable energy, delivering reliable, low-emission baseload electricity and heating solutions. This review bridges the current knowledge gap by addressing challenges and opportunities for engineers and scientists, especially those transitioning from other professions. It examines deep and shallow geothermal systems and explores the advanced technologies and skills required across various climates and environments. Transferable expertise in drilling, completion, subsurface evaluation, and hydrological assessment is required for geothermal development but must be adapted to meet the demands of high-temperature, high-pressure environments; abrasive rocks; and complex downhole conditions. Emerging technologies like Enhanced Geothermal Systems (EGSs) and closed-loop systems enable sustainable energy extraction from impermeable and dry formations. Shallow systems utilize near-surface thermal gradients, hydrology, and soil conditions for efficient heat pump operations. Sustainable practices, including reinjection, machine learning-driven fracture modeling, and the use of corrosion-resistant alloys, enhance well integrity and long-term performance. Case studies like Utah FORGE and the Geysers in California, US, demonstrate hydraulic stimulation, machine learning, and reservoir management, while Cornell University has advanced integrated hybrid geothermal systems. Government incentives, such as tax credits under the Inflation Reduction Act, and academic initiatives, such as adopting geothermal energy at Cornell and Colorado Mesa Universities, are accelerating geothermal integration. These advancements, combined with transferable expertise, position geothermal energy as a major contributor to the global transition to renewable energy. Full article

This review examines the integration of ground source heat pump (GSHP) systems with energy piles as a sustainable approach to improving energy efficiency in smart cities. Energy piles, which combine structural support with geothermal heat exchange, offer significant advantages over conventional air source heat pumps (ASHPs) by using stable ground temperatures for more efficient heating and cooling. System efficiency can be improved by integrating hybrid systems, cooling towers, and solar thermal systems. While the initial investment for GSHP systems is higher, their integration with energy piles significantly reduces electricity consumption and operating costs, providing a compelling solution for regions with high energy demand and escalating energy prices. Government financial incentives, including subsidies, loans, and tax rebates, can reduce payback periods to less than 10 years, encouraging the adoption of energy piles and GSHP systems. The paper analyzes heat transfer mechanisms in energy piles, particularly the role of groundwater circulation in improving heat dissipation and overall system performance. It also discusses optimized design considerations, performance metrics, and economics, highlighting the critical role of site-specific conditions from thorough site surveys and strategic planning of adaptive management to adjust system operations based on real-time demand in optimizing the benefits of geothermal energy systems. This review serves as a comprehensive guide for engineers and researchers in the effective application of energy piles within urban infrastructure, thereby supporting sustainable urban development and mitigating the urban heat island effect. Full article

This article investigates heating options for poultry houses (or sheds) in order to meet their specific indoor air temperature requirements, with case studies conducted across Australia under conditions similar to those encountered worldwide. Hybrid geothermal–solar (PV)–gas heating systems with various configurations are proposed to minimise the lifecycle costs and GHG emissions of poultry shed heating, which involves six seven-week cycles per year. The baseload heating demand is satisfied using ground-source heat pumps (GSHPs), with solar photovoltaic panels generating the electricity needed. LPG burners satisfy the remaining heating demand. Integrating these systems with GSHPs aims to minimise the overall installation costs of the heating system. The primary focus is to curtail the costs and GHG emissions of poultry shed heating with these hybrid systems, considering three different electricity offsetting scenarios. It is found that a considerable reduction in the lifecycle cost (up to 55%) and GHG emissions (up to 50%) can be achieved when hybrid systems are used for heating. The Pareto front solutions for the systems are also determined. By comparing the Pareto front solutions for various scenarios, it is found that the shave factor, a measure of the GSHP proportion of the overall system, significantly influences the lifecycle cost, while the size and utilisation of the solar PV panels significantly affect the lifecycle GHG emissions. Full article

Germany is undergoing an energy transition. By 2045, fossil fuels will be gradually replaced by clean energy. An alternative option is to use geothermal, solar and wind energy to generate heat or electricity. Currently, an economic model that considers these three energy sources and incorporates the design and installation of the energy system as well as operational costing focusing on the local market is lacking. In this study, we present a concept for a hybrid energy system combining solar, wind and geothermal energy for small, detached houses. We also develop a simplified economic model for the German market and local energy subsidy policies. The model was applied to two different cities in northern Germany, calculating the installation and long-term operating costs of different energy systems and combinations over a period of 100 years, including the consideration of the lifespan of variable equipment. The calculations show that for this small hybrid energy system the initial installation costs can vary from EUR 20,344 to EUR 70,186 depending on different portfolios. Long-term operating costs come mainly from electricity purchased from the grid to compensate for periods of low solar or wind production. In addition, the study included a calculation of the payback period for retrofitting a natural gas heating system. Results show that combining a photovoltaic system with a ground source heat pump, especially in the form of a near-surface heat exchanger, yields a shorter payback period (5 to 10 years). However, the incorporation of on-roof wind turbines into the hybrid energy system may significantly prolong the payback period and is therefore not recommended for use in low wind speed areas. Full article

Geothermal energy exploration, development, and research have been ongoing in Canada for several decades. The country’s cold climate and the push to develop renewable energy sources have driven interest in geothermal energy. Despite this drive, regulatory complexities and competition with other relatively inexpensive energy sources with existing infrastructure have hindered development. As such, interest has grown and waned with changes in the energy economy over several decades, leaving many projects at a standstill. As of January 2023, there are currently no operational geothermal power projects in Canada. Many hot spring pool and spa complexes remain active, and Canada is a leading country in the installation of ground source heat pumps (GSHPs; also called geo-exchange systems). However, in the last decade, the interest in deep geothermal systems has renewed, with many new projects starting up across several provinces and territories. Moreover, projects that had shown limited progress for many years—such as Mount Meager in British Columbia—have begun to renew their development efforts. Research is also expanding within prominent research groups and universities. The areas of focus include both building upon previous studies (such as thermal gradients and the heat flow in sedimentary basins) and researching new methods and resources (such as GSHPs, closed-loop systems, integrated geothermal operations, and hybrid systems, including heat storage). The development is supported by federal, provincial, and territorial governments through grants and the development of regulatory frameworks. Although challenges still remain for Canada to develop its geothermal energy resources, several power, thermal, and co-production projects, ongoing research, funding, and regulatory acts are all moving forward to support geothermal development. This paper aims to study Canada’s geothermal energy update in 2023 regarding the aspects mentioned above. Full article

Ground heat accumulation caused by imbalanced heating and cooling loads in a building can cause the heat-source temperature to increase as the operating age of a geothermal heat pump (GHP) system increases. An alternative system to improve upon this situation is the hybrid GHP system. This study reviews existing research on GHP systems and hybrid GHP systems, variable water flow (VWF) control, and coefficient of performance (COP) prediction. Generally, constant flow control is applied to the circulating pump to provide a flow rate according to the maximum load. The need for VWF control was identified because the hybrid GHP system is used mainly as a heating and cooling heat source system for partial loads rather than the entire building load. Previous studies on predicting the COPs of GHP systems developed prediction models by selecting input values based on mathematical models, collecting data through multiple measurement points, and utilizing data from production environments. The model can be limited by the field environment, and it is necessary to predict the COP using machine learning based on existing field monitoring data. Full article

When the geothermal heat pump system is operated due to an imbalance in the heating and cooling load, the system performance is lowered due to the occurrence of a thermal environment problem in the ground. To solve the performance degradation, a hybrid geothermal heat pump system with an added auxiliary heat source is used. For the efficient operation of the system, it is necessary to check the performance coefficient of the hybrid geothermal system. The coefficient of performance can be monitored based on a mathematical model using a measuring instrument. However, in the case of mathematical models, there are a lot of input data required, and many measurement sensors are required for this. If there is an input factor that is omitted among the necessary input factors, the accuracy of the predicted performance coefficient is lowered or a problem occurs that it is impossible to predict. In this study, we intend to create a model that predicts the coefficient of performance (COP) by using ANNs and SVMs that can accurately predict at low cost using small input factors. Hyper-parameter optimization is performed to increase prediction accuracy in machine learning models. We compared the accuracy of ANN and SVM-based prediction models. In this study, the ANN model showed higher CvRMSE by 5.4% and SVM by 8%. It is expected that the predictive model will be able to be used in the operation of the hybrid geothermal system in the future. Full article

Krakow has an extensive district heating network, which is approximately 900 km long. It is the second largest city in terms of the number of inhabitants in Poland, resulting in a high demand for energy—for both heating and cooling. The district heating of the city is based on coal. The paper presents the conception of using the available renewable sources to integrate them into the city’s heating system, increasing the flexibility of the system and its decentralization. An innovative solution of the use of hybrid, modular heat pumps with power dependent on the needs of customers in a given location and combining them with geothermal waters and photovoltaics is presented. The potential of deep geothermal waters is based on two reservoirs built of carbonate rocks, namely Devonian and Upper Jurassic, which mainly consist of dolomite and limestone. The theoretical potential of water intake equal to the nominal heating capacity of a geothermal installation is estimated at 3.3 and 2.0 MW, respectively. Shallow geothermal energy potential varies within the city, reflecting the complex geological structure of the city. Apart from typical borehole heat exchangers (BHEs), the shallower water levels may represent a significant potential source for both heating and cooling by means of water heat pumps. For the heating network, it has been proposed to use modular heat pumps with hybrid sources, which will allow for the flexible development of the network in places previously unavailable or unprofitable. In the case of balancing production and demand, a photovoltaic installation can be an effective and sufficient source of electricity that will cover the annual electricity demand generated by the heat pump installation, when it is used for both heating and cooling. The alternating demand of facilities for heating and cooling energy, caused by changes in the seasons, suggests potential for using seasonal cold and heat storage. Full article

The installation and operation of geothermal systems increased due to the expectation of good cooling and heating performance due to stable heat source temperatures. In actual geothermal system operations, heat source temperature rises or falls due to an imbalance of heating and cooling energy usage. Problems of source side temperature result in reduced geothermal system performance. The purpose of this study is to develop hybrid geothermal system operation technology to stabilize temperature and improve system performance by utilizing auxiliary heat source system. The auxiliary heat source system is operated by comparing the performance when operating the geothermal heat pump system alone and the performance when operating the hybrid geothermal heat pump system. The performance of a hybrid geothermal system is determined by the circulating water temperature of the geothermal system and the circulating water temperature of the auxiliary heat source system. Hybrid geothermal heat pump system performance is predicted through numerical analysis and collection of hybrid geothermal system performance data at various temperature ranges through field test. An operating method was developed using the predicted performance as the changeover operating point of the hybrid geothermal heat pump system. When applying the development and operation technology, it handled about 11% more load than the existing geothermal system operation. The addition of an auxiliary heat source increases the initial investment cost compared to the existing geothermal system, but decreases energy consumption, confirming that the initial investment cost of 15.3 years is recovered. Full article

Nowadays, many buildings are equipped with various energy sources. The challenge is how to efficiently utilize their energy production. This includes decreasing the share and costs of external energy—usually electrical energy delivered from the grid. The following study presents a qualitative approach with a combined control to solve the problem. The approach is demonstrated using a simulated residential building equipped with a hybrid energy system: a thermal energy storage combined with an electrical heater, a geothermal heat pump and a solar thermal collector. Consequently, the share of renewable energy was increased and, conversely, costs of the external energy from grid decreased by 12.2%. The results were based on a qualitative approach and the algorithm which predicts the need of energy of the building over the next 6 h with the aid of weather forecasting. This approach included a storage tank of 300 L. The energy costs can be further decreased 7.7% by increasing thermal storage capacity and modifying the control algorithm. In all cases, the indoor conditions were kept at a comfortable level. However, if the room temperature is temporarily allowed to slightly drop a few degrees during the heating season, the energy costs were further reduced. Full article

GEOFIT, “Deployment of novel GEOthermal systems, technologies and tools for energy efficient building retrofitting,” is a recently launched 4-year H2020 project funded by the Innovation and Networks Executive Agency (INEA) under the call topic LCE-17-2017: Easier to install and more efficient geothermal systems for retrofitting buildings. GEOFIT is a part of INEA’s Energy Portfolio Low Carbon Economy (LCE), Renewable Energy Technologies (RET) and brings together 24 partners from 10 European countries to work on the development of novel and smart shallow geothermal systems. This paper introduces the project. Full article

In the early design phase of a building, the task of the Heating, Ventilation and Air Conditioning (HVAC) engineer is to propose an appropriate HVAC system for a given building. This system should provide thermal comfort to the building occupants at all time, meet the building owner’s specific requirements, and have minimal investment, running, maintenance and replacement costs (i.e., the total cost) and energy use or environmental impact. Calculating these different aspects is highly time-consuming and the HVAC engineer will therefore only be able to compare a (very) limited number of alternatives leading to suboptimal designs. This study presents therefore a Python tool that automates the generation of all possible scenarios for given thermal power profiles and energy load and a given database of HVAC components. The tool sizes each scenario properly, computes its present total cost (PC) and the total CO ${}_2$ emissions associated with the building energy use. Finally, the different scenarios can be searched and classified to pick the most appropriate scenario. The tool uses static calculations based on standards, manufacturer data and basic assumptions similar to those made by engineers in the early design phase. The current version of the tool is further focused on hybrid GEOTABS building, which combines a GEOthermal heat pump with a Thermally Activated System (TABS). It should further be noted that the tool optimizes the HVAC system but not the building envelope, while, ideally, both should be simultaneously optimized. Full article