Energies

Research

Jump to: Other

23 pages, 5239 KiB

Open AccessFeature PaperArticle

A Modelica Toolbox for the Simulation of Borehole Thermal Energy Storage Systems

by Julian Formhals, Hoofar Hemmatabady, Bastian Welsch, Daniel Otto Schulte and Ingo Sass

Energies 2020, 13(9), 2327; https://doi.org/10.3390/en13092327 - 07 May 2020

Cited by 17 | Viewed by 5219

Abstract

Borehole thermal energy storage (BTES) systems facilitate the subsurface seasonal storage of thermal energy on district heating scales. These systems’ performances are strongly dependent on operational conditions like temperature levels or hydraulic circuitry. Preliminary numerical system simulations improve comprehension of the storage performance [...] Read more.

Borehole thermal energy storage (BTES) systems facilitate the subsurface seasonal storage of thermal energy on district heating scales. These systems’ performances are strongly dependent on operational conditions like temperature levels or hydraulic circuitry. Preliminary numerical system simulations improve comprehension of the storage performance and its interdependencies with other system components, but require both accurate and computationally efficient models. This study presents a toolbox for the simulation of borehole thermal energy storage systems in Modelica. The storage model is divided into a borehole heat exchanger (BHE), a local, and a global sub-model. For each sub-model, different modeling approaches can be deployed. To assess the overall performance of the model, two studies are carried out: One compares the model results to those of 3D finite element method (FEM) models to investigate the model’s validity over a large range of parameters. In a second study, the accuracies of the implemented model variants are assessed by comparing their results to monitoring data from an existing BTES system. Both studies prove the validity of the modeling approaches under investigation. Although the differences in accuracy for the compared variants are small, the proper model choice can significantly reduce the computational effort. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures

Graphical abstract

18 pages, 6970 KiB

Open AccessFeature PaperArticle

3-D Geothermal Model of the Lurestan Sector of the Zagros Thrust Belt, Iran

by Matteo Basilici, Stefano Mazzoli, Antonella Megna, Stefano Santini and Stefano Tavani

Energies 2020, 13(9), 2140; https://doi.org/10.3390/en13092140 - 30 Apr 2020

Cited by 8 | Viewed by 3339

Abstract

The Zagros thrust belt is a large orogenic zone located along the southwest region of Iran. To obtain a better knowledge of this important mountain chain, we elaborated the first 3-D model reproducing the thermal structure of its northwestern part, i.e., the Lurestan [...] Read more.

The Zagros thrust belt is a large orogenic zone located along the southwest region of Iran. To obtain a better knowledge of this important mountain chain, we elaborated the first 3-D model reproducing the thermal structure of its northwestern part, i.e., the Lurestan arc. This study is based on a 3-D structural model obtained using published geological sections and available information on the depth of the Moho discontinuity. The analytical calculation procedure took into account the temperature variation due to: (1) The re-equilibrated conductive state after thrusting, (2) frictional heating, (3) heat flow density data, and (4) a series of geologically derived constraints. Both geotherms and isotherms were obtained using this analytical methodology. The results pointed out the fundamental control exerted by the main basement fault of the region, i.e., the Main Frontal Thrust (MFT), in governing the thermal structure of the crust, the main parameter being represented by the amount of basement thickening produced by thrusting. This is manifested by more densely spaced isotherms moving from the southwestern foreland toward the inner parts of orogen, as well as in a lateral variation related with an along-strike change from a moderately dipping crustal ramp of the MFT to the NW to a gently dipping crustal ramp to the SE. The complex structural architecture, largely associated with late-stage (Pliocene) thick-skinned thrusting, results in a zone of relatively high geothermal gradient in the easternmost part of the study area. Our thermal model of a large crustal volume, besides providing new insights into the geodynamic processes affecting a major salient of the Zagros thrust belt, may have important implications for seismotectonic analysis in an area recently affected by a M_w = 7.3 earthquake, as well as for geothermal/hydrocarbon exploration in the highly perspective Lurestan region. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures

Figure 1

23 pages, 8638 KiB

Open AccessArticle

A Model of a Diaphragm Wall Ground Heat Exchanger

by Ida Shafagh, Simon Rees, Iñigo Urra Mardaras, Marina Curto Janó and Merche Polo Carbayo

Energies 2020, 13(2), 300; https://doi.org/10.3390/en13020300 - 07 Jan 2020

Cited by 23 | Viewed by 4880

Abstract

Ground thermal energy is a sustainable source that can substantially reduce our dependency on conventional fuels for heating and cooling of buildings. To exploit this source, foundation sub-structures with embedded heat exchanger pipes are employed. Diaphragm wall heat exchangers are one such form [...] Read more.

Ground thermal energy is a sustainable source that can substantially reduce our dependency on conventional fuels for heating and cooling of buildings. To exploit this source, foundation sub-structures with embedded heat exchanger pipes are employed. Diaphragm wall heat exchangers are one such form of ground heat exchangers, where part of the wall is exposed to the basement area of the building on one side, while the other side and the further depth of the wall face the surrounding ground. To assess the thermal performance of diaphragm wall heat exchangers, a model that takes the wall geometry and boundary conditions at the pipe, basement, and ground surfaces into account is required. This paper describes the development of such a model using a weighting factor approach, known as Dynamic Thermal Networks (DTN), that allows representation of the three-dimensional geometry, required boundary conditions, and heterogeneous material properties. The model is validated using data from an extended series of thermal response test measurements at two full-scale diaphragm wall heat exchanger installations in Barcelona, Spain. Validation studies are presented in terms of comparisons between the predicted and measured fluid temperatures and heat transfer rates. The model was found to predict the dynamics of thermal response over a range of operating conditions with good accuracy and using very modest computational resources. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures

Figure 1

17 pages, 5943 KiB

Open AccessArticle

A Study on the Operational Condition of a Ground Source Heat Pump in Bangkok Based on a Field Experiment and Simulation

by Yutaro Shimada, Youhei Uchida, Isao Takashima, Srilert Chotpantarat, Arif Widiatmojo, Sasimook Chokchai, Punya Charusiri, Hideaki Kurishima and Koji Tokimatsu

Energies 2020, 13(1), 274; https://doi.org/10.3390/en13010274 - 06 Jan 2020

Cited by 14 | Viewed by 4913

Abstract

The deployment of highly efficient cooling equipment is expected to promote energy savings and greenhouse gas emissions reductions in the tropics. A ground source heat pump (GSHP) has high energy-savings potential for use in Bangkok, Thailand. This study aimed to elucidate the operational [...] Read more.

The deployment of highly efficient cooling equipment is expected to promote energy savings and greenhouse gas emissions reductions in the tropics. A ground source heat pump (GSHP) has high energy-savings potential for use in Bangkok, Thailand. This study aimed to elucidate the operational conditions of a GSHP when used in Bangkok which was expected to achieve a higher efficiency than an air source heat pump (ASHP) over the long term. An operational experiment on a pilot facility in Bangkok and a simulation over a three-year GSHP operation were conducted. As a result of the operational experiment and simulation, the proposed operational condition was that the 90th percentile value of the hourly heat pump (HP) inlet temperature did not exceed 5 °C above that of the hourly annual ambient temperature during the third year of operation. When a GSHP designed based on this condition was utilized for a small government building, the required number of boreholes were 24, 4, and 3 for air-conditioned areas of 200, 40, and 25 m², respectively, which achieved 40% energy savings. Thus, a small-scale GSHP in Bangkok designed based on the proposed condition can achieve high efficiency within space limitations. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures

Figure 1

20 pages, 6404 KiB

Open AccessArticle

Design of Groundwater Heat Pump Systems. Principles, Tools, and Strategies for Controlling Gas and Precipitation Problems

by Sondre Gjengedal, Lars A. Stenvik, Pål-Tore S. Storli, Randi K. Ramstad, Bernt O. Hilmo and Bjørn S. Frengstad

Energies 2019, 12(19), 3657; https://doi.org/10.3390/en12193657 - 25 Sep 2019

Cited by 8 | Viewed by 2685

Abstract

The utilization of groundwater heat pump systems is increasing in Norway, which are currently widely employed for heating and cooling applications in the town center of Melhus. The investigations of the Melhus installations are detecting gas exsolution as a possible trigger for precipitation [...] Read more.

The utilization of groundwater heat pump systems is increasing in Norway, which are currently widely employed for heating and cooling applications in the town center of Melhus. The investigations of the Melhus installations are detecting gas exsolution as a possible trigger for precipitation reaction that causes incrustation of iron and manganese compounds in the systems. This paper discusses risks associated with gas exsolution and considers gas exsolution triggers in a typical Norwegian groundwater heat pump (GWHP) system configuration. The concept of the solubility grade line (SGL) is developed and suggested as a tool for optimizing the design. Based on SGL analysis and the intention of avoiding gas exsolution during heat production, an alternative system design in the same aquifer is presented and compared. The analyses show that the traditional system design is predisposed to gas clogging risks and prone to vacuum pressures in parts of the system. The alternative design mediates the risks by adjusting the well and piping configuration and by applying a backpressure technique. The results demonstrate how the groundwater heat pump system design can be customized according to local aquifer conditions to avoid gas exsolution during operation. It is recommended that the presented method of analysis should be utilized in dimensioning of systems and included in the monitoring scheme of the systems. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures

Graphical abstract

25 pages, 4419 KiB

Open AccessArticle

Thermal Response Testing of Large Diameter Energy Piles

by Linden Jensen-Page, Fleur Loveridge and Guillermo A. Narsilio

Energies 2019, 12(14), 2700; https://doi.org/10.3390/en12142700 - 15 Jul 2019

Cited by 22 | Viewed by 4174

Abstract

Energy piles are a novel form of ground heat exchanger (GHE) used in ground source heat pump systems. However, characterizing the pile and ground thermal properties is more challenging than for traditional GHEs. Routine in-situ thermal response testing (TRT) methods assume that steady [...] Read more.

Energy piles are a novel form of ground heat exchanger (GHE) used in ground source heat pump systems. However, characterizing the pile and ground thermal properties is more challenging than for traditional GHEs. Routine in-situ thermal response testing (TRT) methods assume that steady state conditions in the GHE are achieved within a few hours, whereas larger diameter energy piles may take days or even weeks, thereby incurring significant costs. Previous work on pile TRTs has focused on small diameters up to 450 mm. This paper makes the first rigorous assessment of TRT methods for larger diameter piles using field and laboratory datasets, the application of numerical and analytical modelling, and detailed consideration of costs and program. Three-dimensional numerical simulation is shown to be effective for assessing the data gathered but is too computationally expensive for routine practice. Simpler fast run time steady state analytical models are shown to be a theoretically viable tool where sufficient duration test data is available. However, a new assessment of signal to noise ratio (SNR) in real field data shows how power fluctuations cause increased uncertainty in long duration tests. It is therefore recommended to apply transient models or instead to carry out faster and more cost-effective borehole in-situ tests for ground characterization with analytical approaches for pile characterization. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures

Figure 1

34 pages, 3085 KiB

Open AccessEditor’s ChoiceArticle

Measured Performance of a Mixed-Use Commercial-Building Ground Source Heat Pump System in Sweden

by Jeffrey D. Spitler and Signhild Gehlin

Energies 2019, 12(10), 2020; https://doi.org/10.3390/en12102020 - 27 May 2019

Cited by 32 | Viewed by 6683

Abstract

When the new student center at Stockholm University in Sweden was completed in the fall of 2013 it was thoroughly instrumented. The 6300 m² four-story building with offices, a restaurant, study lounges, and meeting rooms was designed to be energy efficient with [...] Read more.

When the new student center at Stockholm University in Sweden was completed in the fall of 2013 it was thoroughly instrumented. The 6300 m² four-story building with offices, a restaurant, study lounges, and meeting rooms was designed to be energy efficient with a planned total energy use of 25 kWh/m²/year. Space heating and hot water are provided by a ground source heat pump (GSHP) system consisting of five 40 kW off-the-shelf water-to-water heat pumps connected to 20 boreholes in hard rock, drilled to a depth of 200 m. Space cooling is provided by direct cooling from the boreholes. This paper uses measured performance data from Studenthuset to calculate the actual thermal performance of the GSHP system during one of its early years of operation. Monthly system coefficients-of-performance and coefficients-of-performance for both heating and cooling operation are presented. In the first months of operation, several problems were corrected, leading to improved performance. This paper provides long-term measured system performance data from a recently installed GSHP system, shows how the various system components affect the performance, presents an uncertainty analysis, and describes how some unanticipated consequences of the design may be ameliorated. Seasonal performance factors (SPF) are evaluated based on the SEPEMO (“SEasonal PErformance factor and MOnitoring for heat pump systems”) boundary schema. For heating (“H”), SPFs of 3.7 ± 0.2 and 2.7 ± 0.13 were obtained for boundaries H2 and H3, respectively. For cooling (“C”), a C2 SPF of 27 ± 5 was obtained. Results are compared to measured performance data from 55 GSHP systems serving commercial buildings that are reported in the literature. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures

Figure 1

Other

Jump to: Research

22 pages, 7106 KiB

Open AccessCase Report

It Works—Long-Term Performance Measurement and Optimization of Six Ground Source Heat Pump Systems in Germany

by Franziska Bockelmann and M. Norbert Fisch

Energies 2019, 12(24), 4691; https://doi.org/10.3390/en12244691 - 10 Dec 2019

Cited by 12 | Viewed by 3326

Abstract

Long-term studies of ground source heat pump (GSHP) heating and cooling systems for six different buildings (commercial, institutional and multi-family buildings) were conducted in Germany by Steinbeis-Innovationszentrum (SIZ) energy+. Three of them are equipped with borehole heat exchangers, and the others use energy [...] Read more.

Long-term studies of ground source heat pump (GSHP) heating and cooling systems for six different buildings (commercial, institutional and multi-family buildings) were conducted in Germany by Steinbeis-Innovationszentrum (SIZ) energy+. Three of them are equipped with borehole heat exchangers, and the others use energy piles as heat exchangers. This paper deals with a demonstration of the investigated buildings, the measured values and performance, and the obtained results include important findings and experiences, problems encountered and possible preventive measures to avoid mistakes. After ten years of operation, it can be stated that the systems work and achieve their planned efficiency but require constant control and regulation to avoid faulty operation. An analysis of the implemented control strategies shows that, for all these heating and cooling systems, holistically coordinated control strategies that are verified during commissioning are required. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

► Show Figures