Geothermal Heat Pump System Research Articles

Variable Water Flow Control of Hybrid Geothermal Heat Pump System

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.

Dynamic modelling of geothermal heat pump system coupled with positive-energy building

During the last decades, several studies have shown that heat pumps are a promising solution to reach the European Union targets on climate change mitigation, since they satisfy the energy needs for heating, cooling and hot water production employing a single device and using a significant share of renewable energy. However, the full exploitation of the energy-saving potential of heat pumps is a difficult task for designers to achieve, as several factors, such as the variability of outdoor climatic conditions, the control logic of the system and the system configuration, influence the energy performance. High Coefficient of Performance (COP) and low environmental impact make Ground Source Heat Pump (GSHP) systems one of the most suitable technologies for the heating and cooling services, to promote the decarbonization of the building sector, especially in urban areas. The objective of this study is to assess a range of strategies for heat pump systems to achieve optimal performance that can be fully utilized.To do this, the authors analyse the performance of a ‘positive’ office building, located in Swansea University Bay, which is already featured with renewable energy technologies for electricity and heat generation: an integrated photovoltaic roof to generate electricity and a wall-photovoltaic thermal system. The current configuration (‘baseline scenario’) of the building-plant system was modelled in TRNSYS 17 environment and the influence of different parameters on the energy performances was studied. To complement the already high use of renewables the authors propose an alternative scenario for the Active Office Building integrating the use of geothermal heat pumps with the existing systems. By comparing the two scenarios on an energy and environmental point of view, it was possible to assess an 11% decrease in primary energy consumption, leading to a corresponding 11% reduction in greenhouse gas (GHG) emissions.

A COP Prediction Model of Hybrid Geothermal Heat Pump Systems based on ANN and SVM with Hyper-Parameters Optimization

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.

A comprehensive study of the thermophysical and rheological properties of ZrO2 based nanofluids as geothermal fluids

Geothermal heat pump systems in residential and commercial applications have become popular in many countries over the past years. The heat transfer performance of the ground heat exchangers in these systems has still room for improvement since they have huge influence on the overall efficiency. Likewise, new heat transfer fluids with enhanced properties, known as nanofluids, have been proposed as a potential solution to substitute the conventional working fluids and to improve the heat transfer processes and performance. A reliable and appropriated proposal of nanofluids for a particular application must include a complete fluid dynamic characterization including thermophysical, rheological, heat transfer coefficients, and pressure drops analysis, as well as physical or chemical characterization of the nanomaterial. In this study, a novel proposal of propylene glycol:water (10:90 vol%)-based zirconium oxide nanofluids of different nanoparticle mass concentrations (0.25, 0.50, 0.75, 1.0, and 5.0 wt%) as possible geothermal working fluids and their thermophysical and rheological characterization are performed. Thus, the nanopowder was extensively investigated by means of Transmission Electron Microscopy, High Resolution Transmission Electron Microscopy, X-Ray diffraction, and Ultraviolet visible spectroscopy obtaining the shape, size distribution, d-spacing, electron diffraction pattern, and crystallinity. Then, thermal conductivities, dynamic viscosities, densities, and isobaric heat capacities for base fluid and nanofluids were measured by transient hot wire, rotational rheometry, vibrating tube, and differential scanning calorimetry methods, respectively. Increases in thermal conductivity, dynamic viscosity, and density of the nanofluids up to 2.8%, 13%, and 4.1% were found, respectively, while decreases in heat capacity reached 11% in comparison to the base fluid. Different models and equations were also employed to analyse the experimental data.

Social and cultural aspects in the adoption of geothermal heat pump systems to replace wood-burning heaters in educational spaces: The Chilean Patagonian case

Due to its high efficiency and zero direct greenhouse gas emissions, the direct utilization of geothermal energy could play a crucial role in addressing climate change. Low-enthalpy geothermal projects, such as geothermal heat pumps (GHPs), have the potential to contribute to greenhouse gases reduction and replace polluting systems like wood burning, which are extensively used in countries such as Chile. The implementation of this technology presents various challenges, encompassing not only economic and technical aspects but also cultural and social factors. This paper addresses the latter two, providing empirical findings from a social and qualitative perspective by examining three GHP projects in educational spaces in Chilean Patagonia.An inductive approach was employed to describe the social perception of GHP projects in three public buildings, specifically educational facilities, located in the Aysén region of Chile. The questions that guided the research were how users interact with technology in these environments and what factors influence their acceptance. Data were collected through various methods, including in-depth interviews and participant observation, with a focus on social perceptions and everyday practices. The paper argues that there is a general lack of information regarding GHP technology. This type of system is often perceived as an ‘elegant’ and almost ‘untouchable’ technology. Nevertheless, motivational factors such as preventing deforestation and reducing air pollution were identified as the primary drivers supporting this type of initiative. One of the cases studied, which demonstrated sustainability over time, revealed that the participants' main motivation was to see themselves as agents of change. This allowed them to build a coherent narrative around the project. Consequently, the cultural meaning attached to the new practice became central for change and sustained adoption of social practices.

A field test of medium-depth geothermal heat pump system for heating in severely cold region

Due to the worldwide attention of fossil fuel consumption and environment pollution, geothermal is recognized to be amongst the prospering alternative energy. Previous researches mainly focused on the shallow-depth geothermal heat pump systems (SD-GHPs), while medium-depth geothermal heat pump system (MD-GHPs) lacked of the experimental support especially in severely cold region. A field test of MD-GHPs using deep borehole heat exchanger (DBHE) was conducted and verified in terms of temperature variation, heat exchange and COP. The indoor temperature remained 20 °C around even though the outdoor temperature was as low as −25.10 °C. The water supply and return water temperature on the customer side performed steadfast heating characteristics that the averages were 35.13 °C and 30.97 °C. Moreover, flow rate and borehole depth are the essential influencing factors on DBHE outlet temperatures. This suggests that lifting flow rates is a fantastic option when only considering the enhancement of the thermal extraction. The DBHE average heat exchange per meter is 1000/1200 m for 61.1/84.9 W/m and 2000 m is 152.6 W/m respectively. Besides, the average heat exchange of DBHEs for working days was 485.4 kW while during Chinese New Year Holidays was 388.6 kW. Correspondingly, the average COPs for MD-GHPs ground side were 4.5 and 5.2, respectively. Results show that MD-GHPs can be extended to severely cold regions and obtain superior performance.

Multicriteria Design and Operation Optimization of a Solar-Assisted Geothermal Heat Pump System

This work focuses on the determination of the design and operation parameters of a thermal system depending on the optimization objective set. Its main objective and contribution concern the proposal of a generalized methodological structure involving multiobjective optimization techniques aimed at providing a solution to a practical problem, such as the design and dimensioning of a solar thermal system. The analysis is based on system operation data provided by a dynamic simulation model, leading to the development of multiple surrogate models of the thermal system. The thermal system surrogate models correlate the desired optimization objectives with thermal system design and operation parameters while additional surrogate models of the Pareto frontiers are generated. The implementation of the methodology is demonstrated through the optimal design and operation parameter dimensioning of a solar-assisted geothermal heat pump that provides domestic hot water loads of an office building. Essentially, energy consumption is optimized for a desired domestic hot water thermal load coverage. Implementation of reverse-engineering methods allows the determination of the system parameters representing the optimized criteria.

Technical-economic and environmental analysis of implementation of geothermal heat pump system

Technical-economic and environmental analysis of implementation of geothermal heat pump system

RETRACTED: Optimal design and transient simulation next to environmental consideration of net-zero energy buildings with green hydrogen production and energy storage system

The integration of renewable energies to produce required commodities and mitigate environmental effects in developed countries has been investigated and tested recently. This study aims to model and develop a building without getting energy from the grid with four occupants for Kuwait's capital and largest metropolis, one of the most significant cities in the Middle East, for reducing greenhouse gas emissions (GHG). Hydrogen energy is employed as energy storage for this building outside the zero-energy network due to the benefits and applications of hydrogen energy. TRNSYS software was utilized for this simulation, and the transient performance of the previously described ZEB was examined annually using TRNSYS software. The building is powered by solar panels, and any extra electricity generated is considered for the hydrogen production and storage unit for use when there is a lack of solar radiation and the building has to be powered. Hot water is created using an evacuated tube solar collector, and it is then kept in a hot water tank. For cooling and heating load, a geothermal heat pump system with auxiliary heaters is employed. MATLAB software is used to analyze the thermal comfort of occupants using the Fanger model. The findings indicate that 72 PV panels with a 1.46 square foot surface area will be used to supply the building without any power shortages. In addition, the building will have zero energy and will receive its hot water from forty 1.5 m2 solar collectors. The ultimate hydrogen pressure tank will be greater than that of the beginning level. The building's air conditioning system offers annual thermal comfort. Additionally, the provided DHW is always at the predetermined temperature of 55 °C. Finally, the usage of the building's roof space can turn into a ZEB and greatly lower Kuwait's greenhouse gas emissions. Environmentally, the proposed system reduce 33% CO2 emission rate compared with fossil fuel.

Geothermal Heat Pump Production Sustainability—The Basis of the Swiss GHP Success Story

Geothermal heat pump systems (GHP) are the spearhead of geothermal achievement and development, and one of the fastest growing applications of renewable energy technologies worldwide. When Swiss GHP activities started in the late 1970s, market introduction and penetration needed science-based proof of reliable, stable, long-term GHP operation. A special, extended project, realized in a field-laboratory setting, provided this proof. Detailed measurements, as well as numerical model simulations, proved the sustainable operation of the installed GHP system. The measurement setup, the recording of the various time series, and their interpretation are presented. Furthermore, basic perceptions were elaborated concerning geothermal resources behavior in production and regeneration. The Swiss GHP was developed from nothing. Early GHP installation costs halved within 20 years; GHP growth was nearly exponential from 1980 to 2020 (8.5% annually). Drilled borehole heat exchanger (BHE) meters are today around 300,000 m per year; heat delivery of GHPs in Switzerland amounted to 3280 GWh 2020—over 85% of Swiss geothermal direct uses (among others like thermal spas, district heating). Large installations with hundreds of BHEs are now common, and are also used for heating and cooling. The international ranking of Swiss GHP realizations is excellent in terms of annual energy use (TJ/yr/area), and is number one worldwide. Switzerland is a global GHP leader, and the Swiss success story is well documented.

Effects of a Combined Geothermal and Solar Heating System as a Renewable Energy Source in a Pig House and Estimation of Energy Consumption Using Artificial Intelligence-Based Prediction Model.

Simple SummaryA combined geothermal heat pump and solar system (GHPS) was installed at a pig house to check the effects on electricity consumption, greenhouse gas emission (GHE), internal farm temperature, the concentration of noxious gases and growth performance. The GHPS heating system reduced energy consumption and CO2 concentrations. Furthermore, the GHPS system effectively maintained the optimum temperature for pig growth inside the pigsty. Additionally, the artificial intelligence (AI)-based model ‘gene expression programming (GEP)’ was used to predict electricity consumption.This experiment evaluated the performance of a combined geothermal heat pump and solar system (GHPS). A GHPS heating system was installed at a pig house and a comparative study was carried out between the environmentally friendly renewable energy source (GHPS) and the traditional heating method using fossil fuels. The impact of both heating systems on production performance, housing environment, noxious gas emission, and energy efficiency were evaluated along with the GHPS system performance parameters such as the coefficient of performance (COP), inlet and outlet water temperature and efficiency of solar collector. The average temperature inside the pig house was significantly higher (p < 0.05) in the GHPS heating system. Similarly, the outflow temperature was increased significantly (p < 0.05) than the inflow temperature. The results of COP and efficiency of the solar system also indicated that the GHPS is an efficient heating system. The electricity consumption and carbon dioxide gas concentration were also reduced (p < 0.05) in the GHPS system. This study also predicts electricity consumption using an artificial intelligence (AI)-based model. The results showed that the proposed model justifies all the acceptance criteria in terms of the correlation coefficient, root mean square value and mean absolute error. The results of our experiment show that the GHPS system can be installed at a pig house for sustainable swine production as a renewable energy source.

Thermal Impact by Open-Loop Geothermal Heat Pump Systems in Two Different Local Underground Conditions on the Alluvial Fan of the Nagara River, Gifu City, Central Japan

An alluvial fan is a good area to install open-loop geothermal heat pump (GHP) systems due to shallower aquifers, faster groundwater flow, and fewer land subsidence risks. The natural temperature change in groundwater occurs in alluvial fans due to the recharge of river water and faster groundwater flow, and the thermal impact of the open-loop system has not been studied well in such areas. The purpose of this research is to understand the thermal impact of open-loop GHP systems on an alluvial fan. A regional 3D model of groundwater flow with heat transport was created to determine the distribution of flow velocity and temperature of groundwater. After that, two local models with different groundwater velocities were constructed to demonstrate the thermal impact of an open-loop GHP system using one extraction and one injection well. The results indicated that the local model with faster groundwater flow had a smaller thermal impact. The natural temperature change in groundwater causes groundwater temperature to be lower in the summer and higher in winter during the operation in the local model, with faster groundwater flow.

Numerical modeling and parametric study of a dual purpose underground thermal battery

Integrating thermal energy storage with building energy systems can enable flexible building electric demands at buildings to help mitigate the mismatch between electricity supply and demand. A novel building heating and cooling system that integrates a dual-source heat pump with hybrid thermal storage named dual-purpose underground thermal battery (DPUTB) has been developed for reshaping building electric demands. The proposed DPUTB integrated geothermal heat pump system is an original innovation that enables Grid-interactive Energy Efficient buildings. This paper focuses on the study of the novel DPUTB. The DPUTB works as both a thermal storage tank (an inner tank) and a ground heat exchanger (an outer tank separated from the inner tank by the insulation material). High fidelity and computationally effective models are needed to predict the performance of the novel DPUTB. This study has developed a simplified dynamic model for the DPUTB according to heat transfer and energy conservation principles and validated it by using experimental data obtained from testing a small-scale DPUTB apparatus. A parametric study was conducted to identify a design that can achieve the target thermal storage performance of load shift and energy efficiency. The parametric study results show that the inner tank shell thermal conductivity and the phase change material's melting point are the two most influencing factors on the performance of the DPUTB. One single full-size DPUTB with the identified design could provide 1-ton cooling (3.51 kW) with the supply temperature lower than 11 °C for 4 hours in summer after being fully charged in 8 hours. The inner tank filled with phase change material is for cooling thermal storage as a latent tank in the design. However, its capacity can be as high as 60 MJ as a sensible water tank for heating storage in winter. In the future study, the DPUTB model will be incorporated into the dual-source heat pump system for evaluating the overall system performance of demand side management in the long term.

Theoretical-Experimental Analysis of the Performance of Geothermal Heat Pumps for Air Conditioning Greenhouses in Arid Zones

This study shows the results of a simulation tool using the TRNSyS 2017 simulator, validated with experimental data from a greenhouse in an arid zone in northwestern Mexico. Additionally, experimental data on the performance of geothermal heat pumps are shown during the year 2020 in heating and cooling mode. With this information, an average deviation of the simulator for the outlet fluid temperature of the geothermal heat exchanger (GHE) of 2.77% and an average deviation of the coefficient of performance in cooling mode (EER) of the geothermal heat pump (GHP) of 3.7% was obtained. In the experimental study, it was observed that in the last 2 weeks of July and the first 2 weeks of August, the subsoil is saturated, which causes a decrease in the thermal inertia of the GHE. During the experimental study, it was possible to determine that the flow indicated in the GHE to obtain the highest performance of the GHP system in greenhouses in arid zones corresponds to 1 GPM, obtaining an EER of 3.24.

A specially-designed test platform and method to study the operation performance of medium-depth geothermal heat pump systems (MD-GHPs) in newly-constructed project

Medium-depth geothermal heat pump systems (MD-GHPs) use deep borehole ground heat exchangers (DBHEs) to extract heat from the medium-depth geothermal energy with depth of 2–3 km. To study the local geothermal condition and operation performance of MD-GHPs, so as to guide the system design and operation control, a test platform and method are raised and applied in a newly-constructed project, where a DBHE with depth of 2750 m is constructed. Results show that the maximum heat extraction rate of DBHE reaches 450 kW with inlet and outlet water temperature of 5.0 ℃ and 18.9 ℃, and the maximum heat supply rate of heat pump reaches 600 kW with supply and return water temperature of 51.8 ℃ and 40.6 ℃ under continuous operation mode. Then the energy efficiency of heat pump (COP) can still remain higher than 3.60 with renewable energy utilization rate higher than 72.2 % in this maximum load condition. Besides, the DBHE still extracts heat from outside ground to store heat when the heat pump system shuts off, thus the transient maximum heat extraction rate could reach 600 kW or even higher under intermittent operation mode. Finally, the optimization direction of DBHE and heat pump systems are analyzed, so as to improve the overall operation performance of MD-GHPs and achieve better energy conservation effect.

Rule reduction for control of a building cooling system using explainable AI

Although it is widely acknowledged that reinforcement learning (RL) can be beneficial for building control, many RL-based control actions remain unexplainable in the daily practice of facility managers. This paper reports a rule reduction framework using explainable RL to enhance the practicality of the control strategy. First, deep Q-learning was applied to explore the optimal control strategies of a parallel cooling system (ice-based thermal system + geothermal heat pump system) of an existing office building. A set of modularized and interconnected data-driven models was developed using ANNs for pretraining an artificial agent. After exploring the control strategies, the decision-making rules of the agent were reduced using a decision tree. The performance of the reduced-order rule-based control proved comparable to the complex and uninterpretable control strategy of deep Q-learning. The difference in energy savings between the two is marginal at 1.2%.

Control of Heat Transfer in a Vertical Ground Heat Exchanger for a Geothermal Heat Pump System

This paper presents a mathematical model of heat transfer behavior between the liquid inside vertical underground geothermal pipes and the surrounding ground for heating (in the winter) and cooling (in the summer) modes in a ground heat exchanger (GHE) that can optimize its output temperature. The GHE’s output temperature reaches the appropriate value when the water velocity is lowered enough. Subsequently, the proposed model was applied to a case study of a 400-ton geothermal heat pump system (GHPS) at Oakland University, in both the heating and cooling modes, to assess its validity and improve the GHE’s performance. The model was implemented in MATLAB using an ordinary differential equation (ODE) solver. Four different water velocities were used to demonstrate the significant effect of velocity on the loop exit temperature. Model predictive control (MPC) was designed to optimize the GHE’s output temperature by controlling the water velocity, which could reduce the energy consumption used for heat and water circulating pumps. The results reveal that the acceptable range of the water velocity for Oakland University’s GHE was between 0.35 and 0.45 m/s, which ensured that the heat pump system delivered the proper temperature to provide the Human Health Building (HHB) with a comfortable temperature regardless of the season. The suggested water velocity ranges in vertical single U-tube pipes with diameters of De 25 mm, De 32 mm, and De 40 mm are between 0.33 and 0.43 m/s, 0.35 to 0.45 m/s, and 0.38 to 0.48 m/s, respectively.

Heating and Cooling with Heat Pumps – Projects developed in Mexico

This article presents extensive research work on geothermal and aerothermal heat pump systems developed in Mexico. Seven systems are presented: (a) water-water geothermal heat pump for a kindergarten and a water-air and water-water combo geothermal heat pumps for a Hospital for the Mexican Social Security Institute (IMSS) at Los Humeros community in Puebla, both systems working for heating; (b) three water-air geothermal heat pumps for heating/cooling for a laboratory complex at Mexicali B.C.; (c) one water-air geothermal heat pump for cooling for a meeting room at Cuernavaca Morelos; (d) two water-water geothermal heat pumps for pool heating at a Sports Club, and four air-water aerothermal heat pumps for cooling/heating and water heating at a hotel in Aguascalientes, Aguascalientes; and (e) a hybrid system composed of two air-water aerothermal heat pumps and a photovoltaic system in León, Guanajuato.

Heat transfer performance of deep borehole heat exchanger with different operation modes

The deep borehole heat exchanger (DBHE) is an essential component of medium-depth geothermal heat pump systems (MD-GHPs). Compared with the conventional borehole heat exchanger, the DBHE has the advantages of minimal land area need, good seasonal heat storage performance and high efficiency in winter. However, most current DBHE research is focused on a single operation mode, and few studies on multiple operation modes. In this study, a DBHE heat transfer model is developed and its governing equations are discretized using the Finite Difference Method (FDM). The model is then validated using measured data from a real-world engineering project. This is followed by an analysis of the outlet water temperature, heat loss rate, maximum heat affected radius, and rock and soil heat recovery characteristics of DBHE with a variety of run-stop ratios (i.e., the ratio of the running time to the intermission time in a day). The following are the key findings: thermal recovery of rock and soil, as well as DBHE operation stability, are negatively correlated with the run-stop ratio, but DBHE heat loss rate is positively correlated with the run-stop ratio; when the run-stop ratio is 24:0 after 15 years of operation, the heat affected radius of DBHE on the surrounding rock and soil is 91.36 m; the other three run-stop ratios (i.e., 16:8,12:12 and 8:16) maybe reduced by 9.07%, 17.34% and 24.86%, respectively. The results of this study have implications for the design of DBHE with different operation modes.

시추공식 계간축열 시스템을 이용한 4세대 지역난방 공급 및 효율 개선 연구

The purpose of this study was to compare the conventional Geothermal Source Heat Pump (GSHP) System, with Borehole Thermal Energy Storage (BTES) utilized heat pump system in cost-wise criteria. The consecutive operation of conventional GSHP performance decreased annually, and eventually discharged the purpose of the system. Deploying the BTES system with heat pump, thereby accumulating the low-cost heat energy from the summer season and using it to ease the heating load peak, can manage the presented problem, as well as supply the sufficient and stable amount of heat energy. Additionally the estimated heat pump capacity of conventional GSHP was 7,864 kW and BTES utilized system showed 1,781 kW. The land area occupancy also decreased by 25%. The BTES system can successfully decrease the initial facility investment cost and make efficient use of ground space.