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Dimensionless Maps for the Validity of Analytical Ground Heat Transfer Models for GSHP Applications
This article provides plain and handy expressions to decide the most suitable analytical model for the thermal analysis of the ground source in vertical ground-coupled heat pump applications. We perform a comprehensive dimensionless analysis of the reciprocal deviation among the classical infinite, finite, linear and cylindrical heat source models in purely conductive media. Besides, we complete the framework of possible boreholes model with the “hollow” finite cylindrical heat source solution, still lacking in the literature. Analytical expressions are effective tools for both design and performance assessment: they are able to provide practical and general indications on the thermal behavior of the ground with an advantageous tradeoff between calculation efforts and solution accuracy. This notwithstanding, their applicability to any specific case is always subjected to the coherence of the model assumptions, also in terms of length and time scales, with the specific case of interest. We propose several dimensionless criteria to evaluate when one model is practically equivalent to another one and handy maps that can be used for both design and performance analysis. Finally, we found that the finite line source represents the most suitable model for borehole heat exchangers (BHEs), as it is applicable to a wide range of space and time scales, practically providing the same results of more complex models.
Journal Article
Geothermal heat pump and heat engine systems : theory and practice
\"Geothermal Heat Pump Systems: Theory and Practice comprehensively covers the theory, fundamental principles and practical applications of geothermal heat pump systems. It takes an interdisciplinary approach considering the disciplines of geoscience, thermodynamics, heat transfer, and fluid mechanics, while keeping in mind the engineering and practical constraints of the real world.The main focus of this book is geothermal heat pump applications for buildings, however the reader is introduced to the bigger picture of geothermal energy utilization, of which geothermal heat pumps is just one type. Methods and equipment used to convert stored thermal energy into useful energy are also discussed and different ground heat exchangers are considered. Geothermal Heat Pump Systems: Theory and Practice contains end of chapter exercise problems and discussion questions and is accompanied by a website hosting practical design software tools that allow the solution of complex, real problems. It also includes presentation files with lecture slides.\"-- Provided by publisher.
Book
A Study on the Operational Condition of a Ground Source Heat Pump in Bangkok Based on a Field Experiment and Simulation
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.
Journal Article
A synergic topology optimization approach on distribution of cooling channels and diverse-intensity heat sources for liquid-cooled heat sink
The liquid-cooled heat sink is an effective and robust cooling device and has been widely used in the industry. The fluid-thermal topology optimization approaches have been adopted for the heat sink design by many researchers. However, none of these works considered the optimization of heat source distribution. This work focuses on the synergic design of the cooling channels and the layout of heat sources with diverse intensities. A hybrid topology optimization approach is adopted, in which the channels are implicitly described with pseudo-density while the heat sources are considered as moving components. The maximum temperature of the system is taken as the objective and constrained by the fluid power dissipation. In order to avoid unrealistic designs such as suspended structures, the stiffness of the structure is considered as a constraint. Considering when heat sources have diverse intensities, the initial locations of the heat sources could significantly affect the optimal result. Aiming at this problem, a heuristic algorithm that can redistribute the heat sources efficiently during the optimization process by exchanging their locations is developed. The topology optimization is performed with a parallel solver developed in Open Field Operation And Manipulation (OpenFOAM) framework. The numerical tests show that the influence of the heat source distribution on the cooling performance could be even higher than the cooling channel design, and the synergic topology optimization method is an effective way to design high-performance heat sink.
Journal Article
Heat Source Models in Numerical Simulations of Laser Welding
The article presents new possibilities for modifying heat source models in numerical simulations of laser welding processes conducted using VisualWeld (SYSWELD) software. Due to the different power distributions and shapes of a laser beams, it was necessary to propose a modification of heat source models and methods of defining the heat introduced into a welded material in the case of simulations of welding processes using solid-state and high-power diode lasers. A solution was proposed in the form of modification of predefined heat source models in the case of simulations of welding processes using solid-state disc lasers and high-power diode lasers (HPDL). Based on the results of metallographic tests and the acquisition of thermal cycles of real laser welding processes, the process of calibration and validation of the proposed models of heat sources depending on the type of device used as well as the obtained shapes of fusion beads was carried out. The purpose and assumptions of this approach towards creating heat sources were also reported, comparing exemplary stresses and cumulative plastic strain distributions for the calculation variant using a standard and modified heat source model.
Journal Article
Heat Source Modeling and Residual Stress Analysis for Metal Directed Energy Deposition Additive Manufacturing
The advancement in additive manufacturing encourages the development of simplified tools for deep and swift research of the technology. Several approaches were developed to reduce the complexity of multi-track modeling for additive manufacturing. In the present work, a simple heat source model called concentrated heat source was evaluated for single- and multi-track deposition for directed energy deposition. The concentrated heat source model was compared with the widely accepted Goldak heat source model. The concentrated heat source does not require melt pool dimension measurement for thermal model simulation. Thus, it reduces the considerable time for preprocessing. The shape of the melt pool and temperature contour around the heat source was analyzed for single-track deposition. A good agreement was noticed for the concentrated heat source model melt pool, with an experimentally determined melt pool, using an optical microscope. Two heat source models were applied to multi-track 3D solid structure thermo-mechanical simulation. The results of the two models, for thermal history and residual stress, were compared with experimentally determined data. A good agreement was found for both models. The concentrated heat source model reported less than the half the computational time required for the Goldak model. The validated model, for 3D solid structure thermo-mechanical simulation, was used to analyze thermal stress evolution during the deposition process. The material deposition on the base plate at room temperature results in lower peak temperatures in the layers near the base plate. Consequently, the higher thermal stress in the layers near the base plate was found, compared to the upper layers during the deposition process.
Journal Article
Simulation Analysis of District Heat-Source Water Supply System Configurations in Urban Areas with Warm Climates
This study investigates the viability of implementing a district heat-source water supply (DHSWS) system in urban areas of warm regions concerning energy efficiency. The building demand included a hotel, office building, and commercial facility, each equipped with water-source heat pumps and chillers utilizing district heat-source water for cooling, heating, and domestic hot water loads. The district heat supply plant featured a two-pipe heat-source water distribution system. Heat-source water was distributed to buildings via the supply pipe, utilized by individual heat-source equipment, and returned to the plant through the return pipe. Heat-source equipment, such as air-source heat pumps, are installed in the plant to maintain the supply temperature within the range of 13-28 °C. This study evaluates the energy performance of a DHSWS plant with an air-cooled heat pump, cooling towers with built-in auxiliary Chiller Unit (CTCUs), and geothermal utilization. To achieve this objective, a system simulation model was constructed, and annual simulations were conducted. Results indicated a 4.9% energy consumption decrease pre- and post-CTCUs implementation. Furthermore, a 4.3% energy consumption reduction was achievable with the introduction of both CTCUs and geothermal heat.
Journal Article
Comparative Analysis of Levelized Cost of Heat in Implemented and Calculated Heat Supply Systems with Heat Pumps in Ukraine
The adoption of heat pumps in Ukraine is increasing, yet precise data on their economic viability are limited. This study compares the Levelized Cost of Heat (LCOH) in implemented and calculated heat pump systems under Ukrainian conditions. Analyzing real installations and theoretical projects, we assess ground-source and air-source heat pumps, focusing on technical indicators like the Seasonal Coefficient of Performance (SCOP) and economic factors such as the investment costs and discount rates. The findings reveal that promotional materials often underestimate the costs, leading to significant discrepancies in the LCOH. Implemented ground-source heat pump projects have investment costs constituting 20–40% of the LCOH, while for air-source heat pumps, this is 60–65%. The discount rate significantly impacts the LCOH, more than electricity costs. Air-source heat pumps in large buildings offer the lowest LCOH, whereas ground-source heat pumps in small houses have a higher LCOH due to the substantial capital investments. This study concludes that while heat pump systems can enhance energy efficiency and reduce environmental impacts in Ukraine, their economic competitiveness hinges on accurate cost assessments and favorable economic conditions.
Journal Article
A deep neural network surrogate modeling benchmark for temperature field prediction of heat source layout
The thermal issue is of great importance during the layout design of heat source components in systems engineering, especially for high functional-density products. Thermal analysis requires complex simulation, which leads to an unaffordable computational burden to layout optimization as it iteratively evaluates different schemes. Surrogate modeling is an effective method for alleviating computation complexity. However, the temperature field prediction (TFP) with complex heat source layout (HSL) input is an ultra-high dimensional nonlinear regression problem, which brings great difficulty to traditional regression models. The deep neural network (DNN) regression method is a feasible way for its good approximation performance. However, it faces great challenges in data preparation for sample diversity and uniformity in the layout space with physical constraints and proper DNN model selection and training for good generality, which necessitates the efforts of layout designers and DNN experts. To advance this cross-domain research, this paper proposes a DNN-based HSL-TFP surrogate modeling task benchmark. With consideration for engineering applicability, sample generation, dataset evaluation, DNN model, and surrogate performance metrics are thoroughly investigated. Experiments are conducted with ten representative state-of-the-art DNN models. A detailed discussion on baseline results is provided, and future prospects are analyzed for DNN-based HSL-TFP tasks.
Journal Article