Earth Air Heat Exchanger Research Articles

Multi-Objective Numerical Analysis of Horizontal Rectilinear Earth–Air Heat Exchangers with Elliptical Cross Section Using Constructal Design and TOPSIS

This study presents a numerical evaluation of a Horizontal Rectilinear Earth–air Heat Exchanger (EAHE), considering the climatic and soil conditions of Viamão, Brazil, a subtropical region. The Constructal Design method, combined with the Exhaustive Search, was utilized to define the system constraints, degree of freedom, and performance indicators. The degree of freedom was characterized by the aspect ratio between the vertical and horizontal lengths of the elliptical cross-section duct (H/L). The performance indicators for the EAHE configurations were assessed based on thermal potential (TP) and pressure drop (PD). The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was applied for multi-objective evaluation, and a methodology for EAHE is proposed. The problem was solved using FLUENT software (version 2024 R2), which employs the Finite Volume Method to solve the conservation equations for mass, momentum, and energy. The (H/L)T,o = 6.0 configuration showed a 16.4% increase in thermal performance for heating and 15.9% for cooling compared to the conventional circular duct. Conversely, the (H/L)F,o = 1.0 configuration reduced pressure loss by 65.33%. The integration of Constructal Design with TOPSIS facilitated the identification of optimized geometries that achieve a balance between performance indicators and those that specifically prioritize thermal or fluid dynamic aspects, being this approach an original scientific contribution of the present work.

Twisted tapes in solar chimney-earth air heat exchangers for equipment downsizing and passive cooling

Harnessing solar and geothermal energy in hot and arid climates is an effective strategy to reduce building energy consumption. This research investigates integrating Twisted Tapes (TT) into Earth Air Heat Exchanger (EAHE) pipes within a Solar Chimney (SC)-EAHE system, aiming to reduce EAHE pipe length while meeting ventilation requirements and decreasing cooling demand. Two key innovations are introduced: first, this study pioneers the integration of TT into a SC-EAHE system; second, it comprehensively explores TT geometry optimization, analyzing the effects of width ratio and rotation rate across 77 configurations. Numerical simulations are conducted in ANSYS Fluent using the k-ε RNG turbulence model to investigate thermal performance and airflow characteristics. Findings reveal that TT integration results in a 153 % increase in Nusselt number. Additionally, it is shown that a 1 m SC diameter achieves ventilation of 4.8 Air Changes per Hour (ACH) using TT with a width ratio and rotation rate of 0.5, while reducing EAHE pipe length by 2.6 %. Increasing the SC diameter to 1.25 m, with a TT width ratio of 0.6 and rotation rate of 1.25, leads to a 13 % (35 m) reduction in EAHE pipe length while meeting a minimum outlet temperature of 290.15 K and ACH requirements. However, the benefit diminishes beyond a 1.25 m SC diameter. This study contributes to understanding of integrating TT into SC-EAHE systems, addressing the critical need for sustainable energy solutions and offering a novel and energy-efficient approach for passive cooling in extreme climates.

Enhancing building energy efficiency: Numerical analysis of a hybrid thermoelectric ventilation system and earth-air heat exchange with photovoltaic-thermoelectric power integration for heating and cooling loads

The lack of studies on hybrid systems combining thermoelectric ventilation (TEV) and earth-air heat exchangers with a photovoltaic-thermoelectric generator (PV-TEG) as the power supply for the hybrid system is addressed in this research. This study aims to investigate the effectiveness and performance of such a combined system in providing the required thermal load of a building. To simulate the performance of TEV and PV-TEG systems, energy conservation equations for various components of the system were formulated for the quasi-state mode. The performance of the earth-air heat exchanger system was evaluated using the effectiveness-number of transfer units method. The resulting set of algebraic equations was then solved using a MATLAB code. Results indicated significant preheating (5.41–15.03 °C) and precooling (0.7–10.22 °C) effects during the daily hours of 15-February and 15-July, respectively. Additionally, the TEG component effectively reduced PV temperatures by 3.54 °C–16.99 °C in 15-February and 3.99 °C–21.54 °C in 15-July. The system also demonstrated a high monthly useful thermal energy output (1215–1584 kWh) in the cold months (December to March), contrasting with higher monthly useful thermal exergy (712–763 kWh) in the summer months. Furthermore, increasing the number of TEGs from 10 to 50 resulted in significant improvements in the yearly average energy and exergy proficiency indexes (PIya,en and PIya,ex) by 164.97 % and 459.82 %, respectively. The supply air mass flow rate and the length and depth of the earth-air duct were identified as the second and third most influential parameters affecting these indexes. Moreover, the system at CPV concentration ratio of 3 provided the highest PIya,en and PIya,ex of 1.512 and 14.65, respectively.

Techno-Economic Feasibility Study of Earth Air Heat Exchangers for Gas Turbine Inlet Air Cooling

In response to pressing energy crises and environmental concerns, enhancing the performance of existing energy conversion systems, such as gas turbines, and tapping into renewable resources have become critical imperatives. Escalating ambient temperatures poses a notable challenge, hampering the efficiency of gas turbines. This study rigorously explores the feasibility of earth-to-air heat exchangers (EAHEs) as a pragmatic solution to cool gas turbine inlet air. The primary objective is an exhaustive techno-economic analysis evaluating the long-term operational viability of EAHE systems. Employing the Taguchi method, the study optimizes the system geometry and pipe arrangement, focusing on four key control factors: pipe diameter, spacing, length, and depth. The pivotal optimization criterion is the levelized cost of energy (LCOE), encompassing thermal performance and economic viability. The net present value (NPV) and Discounted Payback Period provide supplementary insights into the economic prospects. Integral to the study is a novel and intricate hybrid analytical-numerical model that simulates the long-term transient operation of EAHE. Findings from a detailed case study unveil an optimized scenario yielding an LCOE amounting to 0.071 $/kWh, accompanied by a substantial NPV of 4.5 million dollars.

Numerical Evaluation of the Influence of Different Parameters on the Thermoenergetic Performance of the Earth-Air Heat Exchanger in a Social Housing

Numerical Evaluation of the Influence of Different Parameters on the Thermoenergetic Performance of the Earth-Air Heat Exchanger in a Social Housing

Computational fluid dynamic simulation of earth air heat exchanger: A thermal performance comparison between series and parallel arrangements

This study uses Ansys Fluent to compare the thermal performance of series and parallel earth air heat exchanger (EAHE) systems for cooling. The model was validated using experimental data from published literature and matched simulation results. The sensitivity study examined how length, diameter, and ground surface coverings affected EAHE performance. The relationship between effectiveness and the Number Transfer Unit (NTU) of EAHE was explored along with the soil thermal regime. The simulation results show that the series EAHE can achieve a lower temperature drop than parallel. With an input air temperature of 32 °C and EAHE lengths varying from 10 m to 50 m (in 10 m increments), the 50 m EAHE produced the lowest outlet air temperatures: 27.2 °C for the series configuration and 28.8 °C for the parallel arrangement. Changing the EAHE diameter (4–6 in) results in a ±0.2 °C outlet air temperature drop for both setups. EAHE performed best under short grass soil cover, yielding 1.4 °C and 0.5 °C lower outlet air temperatures, for series and parallel arrangements than the asphalt cover. The pressure drop increased proportionally with EAHE's length. Simulation results indicate a ±6 times larger pressure loss in the series design compared to the parallel setup. The effectiveness-NTU relationship shows that parallel EAHEs are 15 % more effective than series ones.

Analysis of Thermal Comfort of the Building Envelope Using an Earth-Air Heat Exchanger

The constructive elements of a building influence the demand for electrical energy, and optimal decisions can be assessed with the support of software that measures this building's demand more accurately. The objective of this research is to assess the thermal behavior of a residential dwelling located in bioclimatic zone 2 in the southern region of Brazil, seeking energy sources that contribute to improving thermal comfort. The study utilizes parameters that reduce the thermal demand for cooling and heating by installing an earth-air heat exchanger (EAHE) in the prolonged occupancy enviroments (POEs) within the building. The results obtained in the EnergyPlus software show that the adaptive comfort of the model with the Earth-Air Heat Exchanger (EAHE), compared to without it, reduces cold discomfort by 5.4% and increases thermal comfort in the building by 5.2%. Analyzing the annual temperatures of the spaces with the EAHE, it is observed that the outlet temperature of the EAHE duct remains at an average of 23.6°C and 23.8°C for the living room and bedrooms, respectively. From an energy perspective, the electrical energy consumption of the building was reduced by 29.8% when using the EAHE.

Performance Analysis of Galvanized Structures for an Earth-Air Heat Exchanger System

This study presents an investigation on Earth-Air Heat Exchangers (EAHEs), a sustainable and cost-effective alternative for improving thermal conditions in environments. The EAHE consists of one or more ducts buried at a certain depth, and a ventilation system, which allows air to flow through the ducts and exchange heat with the soil. The soil, being warmer than the ambient air during cold periods and cooler during hot periods, facilitates this heat exchange. The research aims to evaluate and compare the potential of the soil and EAHE in a system where a galvanized material, shaped like an ellipse, is attached around the duct. Given the high thermal conductivity of galvanization, this material helps enhance the thermal potential of the soil. Two tests were conducted by altering the horizontal and vertical dimensions of the ellipse while keeping the area constant. The results obtained with the galvanized structure were compared with those obtained without the use of this material. Moreover, the authors compared two different geometries of the structures: a circular one, which had been previously tested, and an ellipsoidal one. Additionally, the thermal potentials of the soil and the system improved as the horizontal length of the ellipse decreased.

Numerical Simulation of Vertical Helical Earth-Air Heat Exchangers Multiobjective Performance Assessment

Numerical Simulation of Vertical Helical Earth-Air Heat Exchangers Multiobjective Performance Assessment

Investigating the dynamic thermal performance of a novel PCM to earth-air heat exchanger: Developing numerical model and comparing thermal performance

Integrating phase change materials (PCMs) into earth-air heat exchangers (EAHE) to form PCM-EAHE systems effectively enhances the efficiency of natural energy utilization. This study proposes a novel PCM-EAHE configuration for the first time, incorporating multiple annular PCM layers and a single cylindrical PCM layer within the duct. Mathematical models for four distinct scenarios were developed and validated against experimental data. The findings indicate that the proposed system outperforms existing PCM-EAHE systems in terms of temperature drop, cooling capacity, average coefficient of performance, and temperature drop factor. Furthermore, positioning multiple annular PCM units along the centerline of the pipe (detached from the pipe wall) enhances the cooling and heating performance of the system, while placing a layer of PCM units on the inner wall of the pipe mitigates heat buildup in the soil surrounding the buried pipe. At the same outlet air temperature, this innovative structural design increases the fresh air handling volume and reduces the length of buried ducts by 44 %–54.5 % compared to existing systems. Over five months of continuous operation in Chongqing, the system demonstrated a maximum temperature drop of 6.91 °C, with the maximum liquid fraction reaching 0.34 and a maximum cooling capacity of 5795.14 W. This research contributes to the advancement of natural energy resource exploitation.

Experimental investigation on the thermal enhancement of spherical macro-encapsulated phase change material assisted soil heat accumulators

Reserved cavities during construction have the potential to serve as the space to efficiently harness shallow geothermal energy resources in light of the underground spaces' rapid expansion. Earth-air heat exchanger technology is an effective way among all the technologies. However, as the heat storage capacity of the surrounding soil gradually diminishes due to the long-term operation of the system, it is recommended to incorporate phase change materials (PCMs) with a stabilized heat storage capacity to improve the overall thermal performance of the system. This research specifically recommends back-filling macro-encapsulated PCMs measuring 15–25 mm in order to prevent backfill contamination caused by PCM leakage. The shells and cores of the PCMs are polypropylene spheres and n-heptadecane. Different volume proportions of macro-encapsulated PCMs are used in the design of modified soil accumulators. 27 groups of orthogonal array experimental tables were made using the Taguchi method to test the improved heat accumulator's performance with different heating sources. According to the results, adding PCMs causes the peak temperature to change and increases overall energy storage by 7.2 %. The most significant factor is the soil moisture content, which accounts for 62.47 % of the overall impact of the PCM's heat storage ratio and total heat storage capacity. With a contribution of 20.41 %, the PCM ratio is ranked second. Furthermore, optimization options for the primary parameters that impact the total heat storage and heat storage ratio of the PCM are offered. This paper offers references for the potential use of the PCM-assisted EAHE system design in real-world engineering applications.

Experimental investigation of earth-air heat exchanger using porous clay vessels for eco-friendly buildings

This study introduces an experimental investigation of a novel direct trend evaporative cooler based on a ground-air heat exchanger (GAHE) using porous clay vessels as an evaporation media under a variety of operational conditions, including air flow rate, inlet air temperature, temperature of inlet water, and in air humidity. The evaluation of the GAHE performance was based on the air-cooling effect, wet-bulb and dew-point efficiencies, energy efficiency ratio, water evaporation rate, specific water evaporation, specific cooling capacity, specific total cost, and CO2 emission rate. The influences of dry-bulb temperature, the incoming air's relative humidity (RH), and six air flow rates ranging from 11 to 25 L/s on the performance are investigated and discussed. Results indicated that increasing the air flow rate leads to an increase in the cooling capacity. Energy efficiency ratio (EER) reaches the highest value of about 25.5 recorded at 3:00 PM with air flow rate = 11 L/s. The lowest EER value is approximately 7.2 when the measured inlet and outlet temperatures are the closest at 7:00 PM, with a flow rate of 25 L/s. Increasing the air flow rate from 11 to 17 L/s increased the wet bulb efficiency, and the airflow rate was inversely proportional to wet-bulb efficiency. The maximum and minimum average dew-point efficiencies are 64% and 58% at 17 L/s and 22 L/s respectively. The water evaporation rate increases by 182.1%, increasing the air flow rate from 11 to 25 L/s.

Numerical investigation of the saturating soil layers' effect on air temperature drops along the pipe of Earth-Air Heat Exchanger systems in heating applications

The study investigates the performance of an Earth-Air Heat Exchanger (EAHE) system, which uses underground pipes to pre-condition incoming air by leveraging the stable temperatures of the earth, thereby enhancing energy efficiency in buildings. A key challenge in heating applications is the heat loss experienced by air as it exits the pipe, which leads to a temperature drop. This study addresses this issue by exploring the impact of different soil layer configurations on reducing the outlet air temperature drop. A numerical analysis was conducted, to simulate various arrangements of soil layers to determine their effect on the outlet air temperature. The soils used include typical soil and sand-bentonite mixtures with moisture contents of 0 %, 10 %, and 20 %. The results indicate that the optimal configuration consists of two layers: an upper layer of one meter of dry typical soil and a lower layer of wet sand-bentonite soil with 20 % moisture content. This configuration yields an outlet air temperature of 20.2˚C, representing a 15.9 % increase compared to a single-layer model. This study provides novel insights by demonstrating that specific soil layer arrangements can significantly enhance the thermal performance of EAHE systems, offering a potential solution to minimize temperature drops in heating applications.

Investigating the Effects of Disturbed Soil Thickness on the Performance of Earth Air Heat Exchanger

Investigating the Effects of Disturbed Soil Thickness on the Performance of Earth Air Heat Exchanger

Estimating the impact of the thermo-physical properties of the multilayer soil on earth-air heat exchanger system performance

This study developed a new method for experimentally measuring and estimating multilayer soil thermo-physical properties. It also tested how multi-layered soil influences an earth-air heat exchanger (EAHE) system in Gödöllő, Hungary. Thus, this research has introduced these combination characteristics that increase EAHE system performance by properly estimating soil multi-layer properties and thermal gradients and their thermal performance effects. New laboratory and theoretical methods can evaluate multilayer soil thermal and physical properties depending on moisture content and density. The first layer had the lowest soil moisture content (6.10 %), the fifth layer had the highest (12.8 %), and the mixed layer had the middle value (9.12 %). The densities of these soil types ranged from 930.49 to 1184.03 kg/m3. When installing the EAHE system, the second layer is better for cooling purposes. Third-layer soil pipe air is 3.74 % hotter than second-layer air. Mixed soil heats and cools moderately. It is 1.74 % hotter and 2 % colder than the second and third layers of soil, respectively.

Use of electrical resistivity tomography measurements for investigation of different grouting materials for very shallow geothermal applications within varying seasonal conditions; Applied on a geothermal earth-air heat exchanger system

To achieve the current climate targets, heat pump systems like very shallow geothermal applications are gaining ground. However, the dimensioning of these ground coupled systems is soil-dependent and thus subject to significant differences in efficiency. Furthermore, the thermal properties of the grouting materials are essential for heat transfer in the direct vicinity of the geothermal application. To provide a non-invasive assessment of relevant soil and grouting characteristics, electrical resistivity tomography (ERT) measurements were performed.In this case, the surrounding of an Earth Air-Heat Exchanger – system (EAHE) with different grouting materials (fine sand and fine sand with bentonite) was investigated. For investigation the electrical resistivity (ER) of initial and modified soil conditions were measured regarding soil texture and moisture content. Thereby, the different grouting materials are clearly identified. Thus, based on the ERT measurements, a characterisation of key soil and grouting material properties for applications focusing on heat transfer in soil has been carried out.Furthermore, the depth of soil disturbance due to the EAHE installation could have been traced.Due to a monitoring over different season (February and May) changes in raw ER data could have been ascribed to temperature changes.

Performance evaluation and multi-objective optimization of a hybrid earth-air heat exchanger and building-integrated photovoltaic/thermal system with phase change material and exhaust air heat recovery

The current study explores the feasibility of employing an integrated system comprising an earth-air heat exchanger (EAHE) unit and a photovoltaic/thermal (HPT) system equipped with a phase change material (PCM) to fulfill the heating, cooling, and electrical loads of a building. In this arrangement, ambient air is heated during cold months by passing it through the EAHE and PCM-based HPT systems, and during hot months, it is cooled by passing through the EAHE unit. Additionally, in warm months, the air exiting the building is utilized to lower the temperature of the PV panels. The electricity generated by the PV panels is harnessed to meet a portion or the entirety of the building's electrical demand. Following the identification of factors influencing the system performance, the multi-objectives genetic algorithm (MOGA) approach is employed to ascertain the optimal values of these parameters, aiming to concurrently maximize both the thermal and electrical output of the HPT-EAHE system. The findings indicated that the optimal HPT-EAHE system can fulfill 132693.3 kWh of heating demand for the building during cold months, address 26536.1 kWh of cooling needs during hot months, and generate 9242.2 kWh electrical power throughout the entire year.

Optimized model predictive control for solar assisted earth air heat exchanger system in greenhouse

Agricultural greenhouses play a crucial role in addressing the threat of climate change to agricultural systems. The greenhouse systems control exhibits nonlinear characteristics and large lag, both affecting the regulation of the greenhouse thermal environment. In this paper, a control strategy was designed to set the dynamic reference value of the control objective of the greenhouse model, considering factors such as solar radiation and the heating capacity of water body. A complete greenhouse model was developed using TRNSYS, and then the model predictive control building and optimization were implemented through MATLAB. The control effects of traditional proportional-integral-differentiation control, initial model predictive control, and optimized model predictive control were compared. The results showed that the regulation of greenhouse temperature was improved by 10.6 % in the coldest mouth compared to the conventional proportional-integral-differentiation control by the optimized model predictive control. During a typical cold month, the violation of constraints was reduced by 29.7 % by dynamically setting the target of the greenhouse with the optimized model predictive control. The performance of greenhouse climate control is enhanced by the proposed optimized model predictive control method, ensuring a stable regulation of the crop growth environment.

Performance improvement of the phase change material-assisted earth-air heat exchanger in summer

Studies confirmed that phase change material (PCM) can improve the cooling potential of an earth-air heat exchanger (EAHE). However, the poor utilization of the PCM unit’s latent heat storage (LHS) capacity and insufficient understanding of energy efficiency hinder its applications in EAHE. To solve these problems, this study made a structural improvement to the PCM unit and proposed a centrally located hollow cylindrical PCM-assisted EAHE (CHCPCM-EAHE). Then, numerical simulations were conducted on this CHCPCM-EAHE through a 3-D model built on the ANSYS FLUENT, and its cooling performance in Chongqing (China) summer was comparatively studied. The results found that the LHS performance of the PCM unit in this CHCPCM-EAHE was improved despite the significant reduction in material volume. Compared to the PCM unit in the previous PCM-assisted EAHE, the maximum liquid fraction and average charged latent heat in all charge–discharge cycles of the PCM unit in this CHCPCM-EAHE were increased by 56.82 % and 10.46 %∼56.43 %, respectively. The results also found that the CHCPCM-EAHE performed better in cooling potential and coefficient of performance (COP). Compared to the conventional EAHE and previous PCM-assisted EAHE, its average cooling capacity increased by 60.12 %∼70.75 % and 4.05 %∼10.96 %, and average COP increased by 47.22 %∼49.02 % and 6.88 %∼8.18 %, respectively.

Machine learning-based multi-performance prediction and analysis of Earth-Air Heat Exchanger

The Earth-Air Heat Exchanger (EAHE) plays a crucial role in global renewable energy utilization. Despite various EAHE models, a machine learning-based multi-performance prediction model is lacking. This study introduces a framework based on diverse machine learning models for precise prediction and comprehensive analysis of EAHE's multiple performance indicators. Initially, the theoretical EAHE model is established and validated. Six feature variables and four target variables are input to generate a dataset for machine learning. Six machine learning models are then selected for training, optimization, and validation. Subsequently, model interpretation and analysis are conducted using SHapley additive exPlanations and Partial dependence plots. Results indicate the optimized-extreme gradient boosting model performs the best, with a determination coefficient of 0.98, root mean squared error of 22.98, and mean absolute error of 8.88, identified as the top multi-performance prediction model for EAHE. Notably, pipe diameter, air velocity, and ground type significantly influence EAHE performance. Complex correlations and mutual exclusions exist among target variables, with a strong negative correlation (−0.59) between the coefficient of performance and payback time, highlighting the challenge of simultaneous improvement. This study presents a valuable framework for predicting and analyzing EAHE performance, crucial for promoting its widespread application and enhancing renewable energy utilization.