Vertical Ground Source Heat Pump Research Articles

Numerically investigating the effect of using nanofluids on the thermal performance and coefficient of performance of a U-tube deep borehole ground source heat pump

In this study, a deep-borehole ground source heat pump was simulated using computational fluid dynamics (CFD) method. The thermal performance and coefficient of performance (COP) of the vertical ground source heat pump simulated with accuracy using CFD for water and 4 different nanofluids as working fluids were investigated. Two nanofluids contained silver and copper metallic nanoparticles and the other two nanofluids contained copper and aluminum oxide nanoparticles. For each of these nanofluids as well as water, the heat exchange rate, total exchanged heat, outlet temperature and COP were calculated and the results were compared together. The results showed that using nanofluids leads to increased exchanged heat. Nanofluids based on aluminum oxide, copper oxide, copper and silver nanoparticles resulted in 4.83, 5.76, 6.9, 7.69 percent increase in total exchanged heat, respectively. In addition to increased exchanged heat, using nanofluids increased the outlet temperature. Also, the results showed that the maximum and minimum increase in COP were 36.5% and 5.2% which were related to using silver and aluminum oxide nanoparticle-based nanofluids, respectively.

Technical Performance Comparison of Horizontal and Vertical Ground-Source Heat Pump Systems

The configurations of ground heat exchangers (GHEs) play a significant role in the efficiency and sustainability of ground-source heat pump (GSHP) systems. However, there is a knowledge gap in understanding the performance differences between the horizontal and vertical GSHP systems in the same project under various heating and cooling demands. In this study, a technical performance comparison between GSHP systems coupled with horizontal ground loops and vertical boreholes under three scenarios of heating-to-cooling ratios (6 : 1, 2.4 : 1, and 1 : 1) was conducted. The simulations were based on a coupled thermal–hydraulic model for unsaturated soils that takes into account realistic ground surface boundary, GHE boundary, and the dynamics of heat pump efficiency. The GHEs were designed based on an experimental site located on the campus of a UK university. Results showed significant differences in the development of fluid temperatures and coefficient of performance (COP) of heat pumps between the horizontal and vertical GSHP systems due to the differences in the soil profiles and temperature boundaries. Both the fluid temperatures and heat pump COPs in the horizontal GSHP system reached a steady annual cycle after 2 years regardless of the heating-to-cooling ratios. For the vertical system, a general downward trend in the fluid temperatures and the COP of the heat pump in the heating mode can be found when a heating-to-cooling ratio was 6 : 1 or 2.4 : 1, while an overall upward trend in the fluid temperatures and the COP of the heat pump in the heating mode can be noted in the case of 1 : 1 heating-to-cooling ratio. Additionally, the heat pump operating in the cooling mode was off most of the time when a heating-to-cooling ratio was 6 : 1 or 2.4 : 1, while a declining trend in the COP of the heat pump in the cooling mode was exhibited in the case of a heating-to-cooling ratio of 1 : 1. The technical comparison reveals that the heating-to-cooling ratios would significantly affect the efficiency and sustainability of both GSHP systems.

A study on heating and cooling requirements for green buildings and refugee settlements

In this study, geothermal-based three different systems are examined comparatively and a decision-making method is used to find the best option to use in refugee settlements. Earth air heat exchanger (EAHE), vertical ground source heat pump (VGSHP), and horizontal ground source heat pump (HGSHP) are evaluated from the viewpoint of environmental impact, performance, economy, and health. This study is the first study related to the evaluation of EAHE and GSHP systems by using the analytical hierarchy process (AHP). It is concluded that EAHE is the best option for refugee settlements; also EAHE is a healthier option for the COVID-19 pandemic.

Experimental Study to Analyze Feasibility of a Novel Panelized Ground-Source Thermoelectric System for Building Space Heating and Cooling

A thermoelectric module is a device that converts electrical energy into thermal energy through a mechanism known as the Peltier effect. A Peltier device has hot and cold sides/substrates, and heat can be pumped from the cold side to the hot side under a given voltage. By applying it in buildings and attaching it to building envelope components, such as walls, as a heating and cooling device, the heating and cooling requirements can be met by reversing the voltage applied on these two sides/substrates. In this paper, we describe a novel, panelized, ground source, radiant system design for space heating and cooling in buildings by utilizing the Peltier effect. The system is equipped with water pipes that are attached to one side of the panel and connected with a ground loop to exchange heat between the cold/hot sides of the thermoelectric module and the underground region. The ground loop is inserted in boreholes, similar to those used for a vertical closed-loop Ground Source Heat Pump (GSHP) system, which could be more than a hundred meters deep. Experiments were conducted to evaluate the feasibility of the developed panel system applied in buildings. The results show that: (1) the average cooling Coefficients Of Performance (COP) of the system are low (0.6 or less) even though the ground is used as a heat sink, and thus additional studies are needed to improve it in the future, such as to arrange the thermoelectric modules in cascade and/or develop a new thermoelectric material that has a large Seebeck coefficient; and (2) the developed system using the underground region as the heat source has the potential of meeting heating loads of a building while maintaining at a higher system coefficient of performance (up to ~3.0) for space heating, compared to conventional heating devices, such as furnaces or boilers, especially in a region with mild winters and relatively warm ground.

Comprehensive analysis of a vertical ground-source heat pump for residential use in Mexico

Ground-source heat pumps are widely used around the world because of their capacity to provide renewable and emissions-free energy for residential use. A vertical ground-source heat pump in an air conditioner mode is studied experimentally and numerically. The geothermal heat pump is located in Mexico, and consists of a single U-tube of 100 m depth, with 41.16 m3 of conditioned space. A computational fluid dynamics analysis of the geothermal heat exchanger and a thermoeconomic analysis of the heat pump are developed to evaluate the thermal performance of the system under the weather conditions of Mexico, and to know the cost allocation per equipment of the system. Results show that the geothermal heat pump provides a comfort temperature with the minimum value of a comfort relative humidity; the most important temperature changes for the geothermal heat exchanger are present during the first 10 m depth; the system decreases its performance when operating in cities with hot ambient temperatures; the irreversibilities present in the system are small, and the cost of the components depends mainly on the capital investment. In addition, the coefficient of performance of the system is of 3.3–3.6.

Energy, economic and environmental GIS–based analysis of shallow geothermal potential in urban areas—A Spanish case example

During the last decades, both population growth and increasingly concentration in cities turn these areas into major consumers of energy, mainly due to heating and cooling energy demanded by residential and commercial sectors. In parallel, the promotion of renewables and policies aimed to decrease fossil fuel dependence and save emissions have addressed mostly solutions based on renewable energy resources. Under this scenario, this paper evaluates the feasibility of vertical Ground Source Heat Pump systems based on the spatial study of the site–specific parameters affecting their performance at a local scale. A GIS–based energy, economic and environmental multidimensional approach is then proposed to analyze the heating and cooling energy demand by considering the urban pattern and the real space available for the installations. The paper explores and compares different Borehole Heat Exchanger Ground Source Heat Pump systems by using the G.POT method applied to residential customers. Two Spanish residential locations are included as case study. From the results, geothermal resource gives highly beneficial results also for cooling energy demand, which is not usually considered in geothermal analysis. The proposed renewable system can be also evaluated from this multidimensional perspective on both commercial and tertiary sector, as well as in other locations with a diversity of heating and cooling energy demand profiles.

Preliminary study of a closed loop vertical ground source heat pump system for an experimental pilot plant (Rome, Italy)

A system for capturing thermal energy is planned for installation at the ENEA-Casaccia centre (Italy). Costs, primary energy requirements, pollutant emissions and seasonal electricity consumption were estimated. The configuration based on four boreholes of different depths and the sizing of the vertical loop (double-U) were performed according to the ASHRAE method. This pilot plant, the first under construction within an Italian research centre, is part of a long-term research project funded by the Italian Ministry of Economic Development. The results of this research could be applied throughout the Italian Tyrrhenian Apennine margin, which is geologically characterised by highly conductive lithotypes.

Prediction of the ground temperature variations caused by the operation of GSHP system with ANN

Ground temperature is an important factor that affects the operation efficiency of ground source heat pump (GSHP) systems. Therefore, it is very important to acquire the ground temperature variations, which can be realized by means of sensor measurements or software simulations. But the monitor system sometimes may be ineffective or inaccurate because of the faulty operation of sensors. And also, the conventional physical models have some limitations in obtaining the detailed ground temperature variations caused by the long term operation of GSHP systems. However, an advantage of the measurement system is that a large amount of monitored data of the ground temperature could be obtained, which provide good solutions for the prediction by black-box methods. In this study, artificial neural network (ANN) was adopted for the prediction of the disturbed ground temperature caused by a vertical GSHP system. Two predictions were conducted with this method. The first is that future variations of the average ground temperature within 100 m deep during the long term operation of GSHP system were predicted with enough accuracy using ANN by 'UseParallel' and 'UseGPU' methods. It has been found that, for the average ground temperature prediction, 'UseParallel' is superior to 'UseGPU' in prediction accuracy, but inferior in calculation speed. The second is that the missing data of the monitored ground temperature variations were supplemented with the ANN model. Mean relative error (MRE), max relative error (MAE), mean square error (MSE) and absolute fraction of variance (R2) of the ANN model are 0.3223%, 9.8999%, 0.5036% and more than 0.9994, respectively. The second ANN model could predict the missing data, but failed in predicting the future detailed ground temperature, which should be further improved in the future.

Applicability of ground source heat pumps as a bioremediation-enhancing technology for monoaromatic hydrocarbon contaminants

Geothermal or ground source heat pumps (GSHPs) are among the highest growing renewable energy technologies used for heating and cooling of buildings. However, despite being a well-established technology, their geo-environmental effects such as impact of the heat on the biosphere is still not thoroughly understood. This study uses FEFLOW software, to simulate heat and mass transport of a vertical closed-loop GSHP system. Transient flow and heat transport results for a multiple borehole system are presented which indicate long-term effects on subsurface temperature. Moreover, the impact of temperature change in a contaminated granular porous subsurface during remediation applications is examined. In particular, as subsurface temperatures are elevated due to geothermal heating, sorption will decrease and biodegradation rates will increase. These effects are examined in the context of contaminant transport, to evaluate the possibility of utilizing geothermal heating as a remediation strategy. The results revealed that temperature changes caused by GSHP operation can significantly enhance biodegradation of hydrocarbon contaminants. For instance, elevated subsurface temperature resulted in 97% reduction in benzene total mass, after one year of GSHP operation for a typical office building in Toronto.

Extending capabilities of Thermal Response Tests in vertical ground heat exchangers: An experiment-based local short-time temperature response factor

This work presents a fast and practical method to determine a characteristic function that predicts a local ground response of vertical ground heat exchangers (GHE) in a short term, which is mandatory when intermittent operation modes are modelled. It expands the use of a Thermal Response Test (TRT) that is recommended previous to the design of a borehole field into a vertical Ground Source Heat Pump (GSHP). These tests are used to provide some ground thermal characteristics, such as ground conductivity or borehole effective thermal resistance. The same device can also be used to measure the undisturbed ground temperature along depth. From the measurements, it has been determined a temperature response factor function that characterizes the ground behavior in a short term as a consequence of a heat pulse. This function is then included into a finite line-source model to simulate the average temperature of the fluid that flows into the borehole pipes along time. In order to validate this method, several additional tests have been performed by the same device used for TRT’s, with intermittent operation modes. For each test, both experimental and simulated average fluid temperatures have been compared. Results present an excellent accuracy; thus, they demonstrate de effectiveness of the method, as well as other advantages: i) fast and accurate; ii) prevents high precomputing times; iii) several uncertainties from measurements disappear when it is used.

Feasibility and performance of ground source heat pump systems for commercial applications in tropical and subtropical climates

The feasibility of installation and performance of vertical ground source heat pump (GSHP) systems for heating and cooling of a typical 9000 m2 office building located in ten metropolitan cities with tropical and subtropical climates are investigated. The heating and cooling loads of the identical building in the ten cities are simulated using the EnergyPlus software. For each location, the design of the GSHP system is performed using the ground loop design (GLD) software, and the performance of the GSHP system is assessed. A multi-year cost analysis is also carried out to assess the feasibility of installation of GSHP systems from an economic point of view. It is found that GSHP systems may not be economically viable for the cities in tropical climates, particularly those near the equator, because of inefficient performance and high cooling demand. Thermal imbalance in soil caused by significantly greater cooling demand than heating demand may further exacerbate the system in tropical cities. However, the implementation of GSHP may turn into a feasible option for some of the tropical cities located near the Tropic of Cancer by adopting special design techniques or including additional hybrid energy sources. GSHP systems seem to be economically feasible and operationally efficient in the cities with subtropical climates where more balance between heating and cooling loads exist.

Meeting the demand: geothermal heat supply rates for an urban quarter in Germany

Thermal energy for space heating and for domestic hot water use represents about a third of the overall energy demand in Germany. An alternative to non-renewable energy-based heat supply is the implementation of closed and open shallow geothermal systems, such as horizontal ground source heat pump systems, vertical ground source heat pump (vGSHP) systems and groundwater heat pump systems. Based on existing regulations and local hydrogeological conditions, the optimal site-specific system for heat supply has to be identified. In the presented technical feasibility study, various analytical solutions are tested for an urban quarter before and after building refurbishment. Geothermal heat supply rates are evaluated by providing information on the optimal system and the specific shortcomings. Our results show that standard vGSHP systems are even applicable in older and non-refurbished residential areas with a high heat demand using a borehole heat exchanger with a length of 100 m or in conjunction with multiple boreholes. After refurbishment, all studied shallow geothermal systems are able to cover the lowered heat demand. The presented analysis also demonstrates that ideally, various technological variants of geothermal systems should be evaluated for finding the optimal solution for existing, refurbished and newly developed residential areas.

Experimental Study on Heat Transfer Mechanism of Ground Source Heat Pump Based Single U-Type Vertical Buried Pipe Inlet and Outlet Spacing

Through the self-developed ground source heat pump ground tube heat transfer mechanism simulation test bench, the purpose of this paper is to explore the heat transfer mechanism of ground source heat pump based on the single U-shaped vertical buried pipe inlet and outlet spacing. The experiment uses the control variable method to measure and record the temperature of each inlet and outlet of the single U-shaped vertical buried pipe and the temperature of each measuring point inside the quartz sand of the backfill material by changing the spacing of the inlet and outlet of the single U-shaped vertical buried pipe. The curve of the temperature of each measuring point inside the quartz sand with time back is drawn and the relation expression is obtained. In addition, the relationship between the temperature difference between the inlet and outlet and the distance between the buried pipes is obtained. The relevant results and conclusions of this experimental study can provide scientific guidance for the practical application of a single U-shaped vertical buried-tube ground source heat pump.

Impact of building thermal load on the developed thermal plumes of a multi-borehole GSHP system in different canadian climates

The environmental impacts and unsustainability of fossil fuel-based heating and cooling systems has encouraged a worldwide interest in developing sustainable sources of energy and complementary technologies for heating/cooling purposes. One of these technologies is ground source heat pump (GSHP) systems that use the ubiquitous low-enthalpy ground source heat found in the shallow subsurface and represents a sustainable way of heating and cooling homes and buildings. GSHPs can be used to extract or inject subsurface heat by installing boreholes that circulate an antifreeze-based carrier fluid which is cooled or heated through the subsurface. Although GSHPs have many advantages, they might develop subsurface thermal plumes, which can affect the efficiency and sustainability of the system and other subsurface infrastructures. In the present research, the effect of a multi-borehole vertical GSHP system designed to deliver annual heating and cooling to an office building located in three Canadian cities was examined. This was done using a three-dimensional model, developed in FEFLOW, that simulated a hypothetical GSHP system in all three cities. It was found that the city with the highest thermal load resulted in the biggest subsurface thermal plume showing a direct connection between building thermal load and thermal plumes. Cyclical simulations for 10 years showed that the plumes grew in both size and temperature disturbance after the 10-year operation. The developed model can be used to determine the thermal affected zone of a GSHP system to aid in planning of other subsurface infrastructures in that zone.

Energy, exergy and exergoeconomic analysis of solar-assisted vertical ground source heat pump system for heating season

The purpose of this study is to evaluate the experimental performance of a solar assisted vertical ground source heat pump system (VGSHP) for the winter climatic conditions of Mardin, which is in the South-Eastern Anatolia region of Turkey. For this aim, an experimental analysis was performed on solar assisted VGSHP system, which was designed to meet the heating needs of an experimental room, during the heating season (10.01.2013/03.31.2014). The experimentally obtained results were used to calculate energy, exergy and exergoeconomic analyses of the system and its components. The energy efficiency, exergy efficiency and exergoeconomic factors of the entire system were 67.36 %, 27.40 % and 60.51 %, respectively. In this study, the system was proposed for disseminating the use of alternative technologies supported by renewable energy systems and it has been tested for the first time in Mardin to meet its heating needs with convectional systems. The experimental results showed that the proposed solar assisted VGSHP system can be used for residential heating in Mardin and similar regions. As a result, it has been detected that the system is very effective in both reducing energy consumption and decreasing emissions of green-house gases.

Restoration performance and operation characteristics of a vertical U-tube ground source heat pump system with phase change grouts under different running modes

This work investigates the effects of different operation modes on the restoration performance and operation characteristics of a ground source heat pump (GSHP) system backfilled with phase change materials (PCM). A numerical GSHP system model considering site conditions and dynamic loads was developed and validated. The effects of daily working schedules, load features and operation schedules of short time period operation modes, and phase-transition temperature of PCM grout were explored. The results show that PCM grout is more suitable for buildings with less-persistent thermal demand considering the importance of restorability. Operating the GSHP with cooling & heating alternate load is the most effective way to improve the overall performance of the system, but a suitable operation schedule should be used. Decreasing the cycle ratio is the best method to promote the system performance under the same hourly load intensity, while for the operation schedules with higher hourly load intensity, a shorter cycle period is recommended. The phase-transition temperature of PCM grout influences the system stability and sustainability greatly as it controls when the melting occurs. The grout with the phase-transition temperature of 20.4 °C is demonstrated to be the most suitable one under our conditions as it provides relatively stable and effective performance over the entire summer and has a higher utilization ratio of the latent heat.

Evaluation of a transient borehole heat exchanger model in dynamic simulation of a ground source heat pump system

The performance of a vertical ground source heat pump system (GSHPS) largely depends on the fluid temperature leaving the borehole heat exchanger (BHE) that may be affected by the short-term behavior of the BHE. Although considerable research has been carried out to analyze the short-term transient response of the BHEs, few studies have investigated its impact on dynamic simulation of GSHPS. Therefore, this paper presents a numerical approach based on a transient BHE model to evaluate the performance of a residential GSHPS over short and long timescales. The numerical results are compared with the results of EnergyPlus software. It is shown that the proposed model can appropriately predict the dynamic behavior of the system. Moreover, effect of borehole thermal capacity on the performance of the GSHPS is investigated in comparison with a quasi-steady state model. It is found that including the borehole thermal capacity substantially affects the design borehole length. Using the transient model instead of the quasi-steady state model leads to a 16% reduction in the required borehole length.

Heat pump technology: An Alaska case study

Heat pumps are a proven technology around the world and are being increasingly used in Alaska. Technological advances have improved their performance at low temperatures, making them more suitable for arctic environments. This analysis identified data related to 17 heat pumps installed in Alaska, which included air source, ground source, and sea water source systems. The data show that the average installed cost/kW of the heat pumps studied was $5,579. The minimum cost was just over $700/kW for a small air source minisplit system and over $12 000 for a complex vertical loop ground source heat pump. Air source heat pumps in Alaska have operated successfully down to −15 °C. Technological advances are ongoing that should enable further heat pump operation in colder climates.

Damage event analysis of vertical ground source heat pump systems in Germany

In recent years, some spectacular cases of damage occurred with vertical ground source heat pump (GSHP) systems in Germany. Broad media coverage attracted enormous public attention, with reports about land subsidence and ground uplifts causing severe damage to buildings. Consequently, sales of vertical GSHP systems have declined. The current study develops conceptual models illustrating the causes and effects of damage in relation to geological and hydrogeological settings. Our investigations revealed nine cases of serious damage in Germany, causing financial losses of more than 100 million Euros. In most cases, connection of aquifers by leaky annular space grouting was the main cause of damage. Guidelines to regulate the installation of vertical GSHP systems have been introduced successfully in all federal states. However, further risk minimisation strategies must be developed to restore the public’s confidence in GSHP technology. Quality assurance and quality control measures should include in particular the optimisation of backfilling materials and increasing use of monitoring systems.

Economic analysis of vertical ground source heat pump systems in Melbourne

This study assesses some economic indicators for residential vertical Ground Source Heat Pump (GSHP) systems in Melbourne, Australia. Publicly available data on the performance and costs associated with such systems is rare. To redress this issue, detailed cost breakdowns are reported herein based on actual installation costs. The average upper bound capital cost is found to be around AUD 31,000, with lower costs possible depending on many factors, particularly when considering the early stage of development of the GSHP industry in Australia. Using the gathered cost data as well as other performance data such as recorded average coefficients of performance of 3.8 and 3.6 for heating and cooling respectively, several economic indicators are used to evaluate alternative heating/cooling systems. The analyses found that for a design life of 20 years, an Air Source Heat Pump (ASHP) system is marginally more financially attractive than a GSHP system; however, for a design life of 40 years, GSHP system provide considerably more savings than other alternatives including ASHP systems. The relatively low rate of return for GSHP systems over the first 20 years is due to current high capital costs as well as the mild weather conditions in Melbourne. Climate change was also factored into the economic analyses, with only minor effects observed. Finally, a scenario with government incentives was found to make GSHP systems much more financially attractive, a tax credit on capital cost of as low as 8% was found as such threshold for a design life of 20 years.