Earth Air Heat Exchanger System Research Articles

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 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.

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.

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.

Efficient operation of earth–air heat exchanger system for air cooling in a hot climate based on a new control strategy

The present research contributes to filling a gap not covered in the previous studies on shallow geothermal applications using earth-to-air heat exchanger (EAHE) systems. The authors think that operating the EAHE continuously for long periods, as presented in many of the previous studies, is not efficient, and this is due to the following reasons:- At specific periods, especially during the night and early morning, the difference between the ambient air temperature (Tamb) and the undisturbed ground temperature (UGT) is small and even negative, meaning the ambient air is colder than the ground.- The continuous operation of the EAHE for a long time leads to the ground saturation with heat, which means that the ground cannot absorb more heat from the EAHE inlet air.So, the present study investigates performance improvement by applying a control strategy to the EAHE system according to two different modes: mode 1 and mode 2. These two operational modes depend on the difference between the ambient air temperature and the UGT value. In mode 1, the ambient air flows inside the EAHE and supplies fresh air to the building. This mode is applied when the temperature difference (Tamb-UGT) exceeds 1.5 οC. When the condition of mode 1 is not satisfied, mode 2 is used, where the ambient air bypasses the EAHE and is supplied directly to the ventilated space. To carry out the present investigation, a numerical model of the EAHE system is developed, and its results are validated against published data from the literature.The simulation of EAHE in Madinah City, KSA, presenting a hot climate region, has been carried out. The study's results confirmed that the control strategy is an efficient solution for the continuous operation of the EAHE. The applied control strategy guarantees that the air supplied to the building is the coldest among the ambient air and the EAHE outlet air. Also, it has been shown that when the control is applied (mode 2), the temperature of the air supplied to the building is 1.5 °C lower than that of the case related to mode 1. Finally, the results showed that the ground can be recovered thermally when the air bypasses the EAHE (mode 2). The ground temperature recovers almost to its undisturbed value during specific periods, which enhances the potential for subsequent heat absorption.

Utilization of least squares support vector machine for predicting the yearly exergy yield of a hybrid renewable energy system composed of a building integrated photovoltaic thermal system and an earth air heat exchanger system

In the present research, the least squares support vector machine technique is employed to develop a relationship to predict the total useful exergy yield of a hybrid renewable energy system consisting of a building integrated photovoltaic thermal (PVT) system and an earth air heat exchanger (EAHX) system. This system is designed to bring the temperature of the ambient air to the desired temperature and also to supply the required electricity of the building. In the cold months of the year, the ambient air is preheated by passing through the PVT and EAHX systems. In the hot months of the year, the ambient air is pre-cooled by passing through the EAHX system, while the air leaving the building is also used to cool the photovoltaic panels. The electricity produced by photovoltaic panels is used throughout the year to meet the electricity needs of the building. The dimensions of different parts of the PVT and EAHE systems along with air flow rate are considered as the main variables and the annual exergy yield of the hybrid system is considered as the dependent variable. The LSSVM model in terms of (R = 0.9670, RMSE=1,152,165.21, and MAPE=29,264.80) resulted in promising outcomes to simulate the useful exergy.

Evaluating the energy-saving potential of earth-air heat exchanger (EAHX) for Passivhaus standard buildings in different climates in China

The significance of constructing low-carbon buildings has been on the rise because of the growing public concern about global warming and energy prices. The Passive House (or Passivhaus) standard is widely applied throughout Europe to reduce building energy consumption. However, a large percentage of the world’s population lives in regions with not only heating demand in winter but also high cooling and dehumidification energy consumption in the hot and humid summer, such as in several regions in China. The energy consumption of buildings in these regions could not be reduced by designing or retrofitting the buildings to Passivhaus standard only, but applying appropriate low energy cooling and dehumidification technologies are also necessary. The earth-air heat exchanger (EAHX) system is a suitable solution for utilizing low-temperature soil in summer, but the performance of the EAHX system in different climates was not previously evaluated. Thus, this research aims to evaluate the energy-saving potential of the EAHX system in a multi-storey Passivhaus standard building in different cities in China with different climatic conditions. A model of the Passivhaus building with the EAHX system was developed and verified using the Passive House Institute (PHI) prediction tool, PHPP and the commercial building energy simulation tool, IES Virtual Environment (VE). The results have shown that the EAHX system achieved an annual building energy load saving of up to 12.8 kWh/m2 in regions with hot and humid summers and cold winters, such as Beijing and Shanghai. The present study shows the potential of the addition of the EAHX in enhancing the building performance to satisfy the Passivhaus standard in hot and humid climates.

Multi-objective energy and exergy optimization of hybrid building-integrated heat pipe photovoltaic/thermal and earth air heat exchanger system using soft computing technique

This research is dedicated to the numerical assessment of the performance of a novel system that uses solar and geothermal energy at the same time, which is capable of heating/cooling the outside air before it enters the air conditioning system of a building and supplying the required electricity for the building. The desired system consists of a photovoltaic/thermal-heat pipe (PVT-heat pipe) unit and an earth-air heat exchanger (EAHE). To cool the outside air in hot seasons of the year, the air is passed through the EAHE system and the exhaust air from building is used to cool the photovoltaic panels. Outside air heating in cold seasons is also possible by passing air through the PVT-heat pipe and EAHE systems. The genetic algorithm-based two-objective optimization is used to determine the necessary conditions to simultaneously maximize the annual useful energy and exergy yields of the hybrid system. The performance metrics of the optimal system are compared with the corresponding values of the PVT-EAHE unit. Outcomes revealed that the annual useful energy output of the PVT-heat pipe-EAHE system (93925.6kWh) is less than the PVT-EAHE system (96448.6kWh), while the PVT-heat pipe-EAHE system is able to produce more exergy (10904.5kWh) than the PVT-EAHE system (10015.5kWh).

The Earth-Air Heat Exchanger System Performance Combined with a Solar Collector for Cooling an Indoor Space Room in Medan City

Cooling systems such as ventilation and air conditioning in rooms, offices, and homes have become one of today's most significant energy consumption aspects. Therefore, to reduce energy consumption, it is necessary to save energy. One way to save energy is by creating an alternative cooling system that does not consume electrical energy. One of them is the cooling system using the earth-air heat exchanger (EAHE). The research objective was to determine the EAHE system's performance combined with a solar collector for cooling an indoor space room in Medan city. This research is interesting because it utilizes cold temperatures from underground for a cooling system. The innovation obtained is a simple technology for the cooling process without depending on electrical and mechanical energy. The testing room has dimensions of 200 cm x 200 cm x 200 cm. Testing using a flat plate type solar collector to help air movement by taking advantage of air temperature differences. The testing process starts at 08.00 WIB to 17.00 WIB for several days. The measurement taken includes weather conditions include solar radiation intensity, ambient temperature, and air humidity. During the test, the solar radiation intensity ranged from 62.71-893.43 W/m2, the variation in ambient temperature from 24.65-35.26oC, and the average air humidity 69.80%. The experimental data showed that indoor air temperature fluctuation ranged from 23.01oC to 31.84oC, and the average room temperature was 27.71oC. This study resulted in an average effectiveness value of the EAHE system of 51.56%.

Performance of earth-air heat exchanger in cooling, heating, and reducing carbon emissions of an industrial poultry farm: A case study

ABSTRACT This paper aims to study an earth-air heat exchanger system proposed to cover the living environment needs and reduce energy consumption and greenhouse gas emissions of an industrial poultry house in southern Algeria. For this purpose, a detailed mathematical model was used to determine the thermal needs of this industrial building. The soil temperature was studied to estimate the appropriate depth for installing the earth-air heat exchanger, followed by a parametric and economic study to determine its dimensions and cost. Finally, compare its performance with the systems currently used in this industrial farm. The study results, which were obtained in extreme working conditions, showed that the earth air heat exchanger could cover 45% and 38% of the heating and cooling demands, respectively. In summer, the proposed heat exchanger was able to reduce the temperature from 47°C to 27.1°C, while in winter, it was able to increase the temperature from 4.8°C to 22.9°C, and its performance was stable compared to the systems currently used, and, it recorded temperatures better under hot outside conditions. Furthermore, its use reduces CO2 emissions to 719 kgCO2/day in heating and 2531 kgCO2/day in cooling, making it a suitable solution for this type of industrial building.

Impact of an Earth-Air Heat Exchanger Combined With Nighttime Ventilation on Indoor Thermal Comfort of a Residential Building in Hot Semi-Arid Climate

Abstract This work aims at investigating the impact of an Earth-Air Heat eXchanger (EAHX) on the thermal comfort when it is added to a natural nighttime ventilation for a house located in Marrakech (Morocco), which is characterized by a hot semi-arid climate. The thermal behavior of the house associated with this cooling combination was assessed using dynamic simulations. Two transient models are used, the well-validated Type 460 model of trnsys software (Transient System Simulation) for the EAHX and a separate trnsys-based model for the building, recently validated using an onsite long-term monitoring of the house under study in the present work. Many configurations of the house ranging from the building without any passive technique to the building with envelope thermal insulation connected with the EAHX combined with natural nighttime ventilation strategy have been investigated. The results showed that the nighttime ventilation strategy alone keeps the operative temperature lower than the convenient 28 °C for 92% of the time during the cooling period. On the other hand, when the EAHX alone is used, the operative temperature is lower than 28 °C during 57% of the time during the hot season. Hence, it was concluded that the passive nighttime ventilation alone leads already to a great thermal comfort improvement; however, its combination with an additional EAHX system results in convenient temperatures lower than 28 °C for 99% of time during the complete cooling period. It is found also that by applying nighttime ventilation, the air blowing flowrate can be reduced by up to three air change per hour while keeping the same EAHX’ parameters.

A brief review of pre-installation requirements of earth-air heat exchanger system for space heating and cooling.

Demand for renewable energy sources has increased significantly during the past 15-20years. Due to this demand, one positive scenario has occurred as there has been a decrease in the use of fossil fuels. Among various usages of the fuels, a significant amount of energy is being used in heating and cooling for commercial, domestic houses, etc. Traditional air conditioning systems use a lot of energy and are particularly inefficient in tropical countries. Earth-air heat exchanger (EAHE) systems can help to reduce the air conditioning demand while also promoting the development of renewable energy. This paper focuses on a review of previous research on this notion for system installation done by earlier researchers. Researchers working on efficient heating and cooling for human comfort will benefit from this review article. The researchers working on EAHE for heating and cooling will benefit from this review paper because it will give them the basic knowledge they need to begin their experimental work.

Experimental investigation of natural ventilation characteristics of a solar chimney coupled with earth-air heat exchanger (SCEAHE) system in summer and winter

The coupled effect of the solar chimney (SC) and earth-air heat exchanger (EAHE), as a pure passive system, is expected to generate natural ventilation with a cooling/heating potential. This study aimed to experimentally evaluate the natural ventilation characteristics of SCEAHE system in both summer and winter. The results showed that under the regulation of SCEAHE system, indoor air temperatures below 29 °C accounted for 78.6% of the total 168 h in summer, whereas indoor air temperatures above 5 °C accounted for 77.4% during the winter. The driving force for nocturnal ventilation was generated by the coupled effect of the thermal mass and subsoil in summer, whereas the same was generated by only the subsoil in winter. This shift in buoyancy forces ensured continuous nocturnal natural ventilation for an annual cycle. The continuous and periodic airflow rates varying from 56.5 to 291.5 m³/h, and from 90.9 to 388.8 m³/h were observed during the summer and winter, respectively. Therefore, the SCEAHE system was able to provide continuous natural ventilation, even under the cloudy weather condition. In addition, the average thermal efficiency of the system was 0.61 in the summer, while the average value was 0.86 in the winter.

Experimental studies on natural bank type heating/cooling energy saving Air conditioning system

The present study reports air-based novel energy saving compact bank type earth air heat exchanger system (EAHE) (having only 25m2 area) fabricated from Polyvinylchloride pipes of nominal diameter 0.203 mm (8 inches) for inlet and outlet headers and main pipes and 0.150 mm (6 inches nominal diameter) for branched pipes, which is installed in Shaheed Bhagat Singh State University, Ferozepur in Punjab state, India (North West border area of India) and studied for the duration from April to August 2021 using the full factorial design with four inlet variables at multilevel to find a model equation between inlet and outlet variables, i.e., heat exchanger effectiveness and achieved temperature difference. An induced airflow mode has been used to provide near-uniform flow through all corresponding pipes of symmetrical-shaped earth air heat exchangers. The values of Dry bulb temperature (DBT) and wet bulb temperature (WBT) have been measured for air inlet, for air outlet, as well as for ambient air using resistance temperature detectors (RTD) installed at the requisite locations. Earth's undisturbed temperature (EUT) was also noted by installing RTD at a depth of 2 m, and the average measured value of EUT is found to be 28.5°C. The current system has imparted the temperature difference variation from 0.4 oC to 9.4 oC, and the effectiveness varied from 0.16 to 0.82 during the whole season. This system could give a cooling potential of 0.0523 kJ/s to 1.587 kJ/s using a mass flow rate of 0.163 kg/s.Experiments have been designed methodically to apply the full factorial technique. Most favorable parameters have been found for hot and dry and hot and humid weather. The current study is novel in terms of significantly improving the effectiveness of EAHE and addressing the central issue of space limitation in urban areas.

Investigation on the cooling performance of a buoyancy driven earth-air heat exchanger system and the impact on indoor thermal environment

The feasibility and cooling performance of a pure buoyancy-driven earth-air heat exchanger system (B-EAHE) with the assistance of combined effect of solar chimney and thermal mass were verified and revealed by a full-scale experimental study. The experimental results showed that the EAHE pipe diameter plays an important role in the system performance, and the airflow rates reach peak values of approximately 252 m3/h and 166 m3/h for the EAHE pipes with diameters of 0.3 m and 0.2 m, respectively. The air temperature differences between the inlet and outlet of the EAHE were approximately 12.5 °C and 13.0 °C in maximum, and 4.8 °C and 4.78 °C in average for the EAHE pipes with diameters of 0.2 and 0.3 m. In addition, the amplitude of indoor air temperature was further attenuated under the regulation of the B-EAHE system. The air temperature inside reference chamber varies from 28.3 to 35.1 °C, while the air temperature inside test chamber with 0.3 m diameter pipe ranges from 28.5 to 30 °C, which is approximately 2 °C lower than that for test chamber with 0.2 m diameter pipe. Moreover, higher energy saving potential is justified by the 0.3 m diameter pipe with peak cooling capacity of 1179 W compared with the 0.2 m diameter pipe with peak cooling capacity of 629 W. It is concluded that the B-EAHE system is able to achieve 24 h periodically fluctuating natural ventilation and passive cooling, and to improve the indoor thermal environment greatly in hot summer conditions.

Thermal potential improvement of an earth-air heat exchanger (EAHE) by employing backfilling for deep underground emergency ventilation

Backfilling can enhance the thermal potential of an earth-air heat exchanger (EAHE) system, but traditional researches are hindered by the shallow buried/horizontal conditions or the limitation of air temperature concerned only. This present research fills in an important research gap by investigating the effect of backfilling on both heat and mass transfer of an EAHE system for deep underground emergency ventilation. The advanced numerical model is established and the agreements with field test data are satisfactory. The effect of the backfilling system has been investigated and the possible improvement has been identified. The results show that the effect of the backfilling technology is of almost equal significance to the EAHE system in some cases, and the upper limit of application depth for the backfilling technology is found. Successful deployment of the backfilling system will assist the emergency ventilation on its process towards energy-efficiency and thermal comfort, and the backfilling system can further improve the thermal performance up to 100% on the basis of the original system. However, backfilling is not an appropriate method for EAHE system under 400 m depth. And there is no need for the thermal conductivity of backfilling materials to be higher than 2.5 W/(m·K).

Experimental and numerical study on the cooling performance of a new earth-air heat exchanger(EAHE) system with a supply air static pressure chamber

Earth-air heat exchanger (EAHE) is a low-carbon device that use renewable energy to improve the thermal environment of buildings by heating/cooling the air with the help of the thermal inertia of the soil. However, the traditional earth-air heat exchanger has the problem of large fluctuations in air temperature with the outdoor air temperature fluctuations. A system that combines an air supply chamber with an EAHE is proposed to address this problem. The outdoor air first enters the underground air supply static pressure chamber for initial cooling, and then enters the EAHE treatment. To investigate the effect of this air supply static pressure chamber on the cooling performance of EAHE, a three-dimensional numerical model was developed in ANSYS Fluent and validated with field measurement data. Then comparative studies of the EAHE system with a supply air static pressure chamber and the traditionnal EAHE system were conducted under summer conditions in Chongqing (China). The results show that the air supply static pressure chamber can reduce the EAHE outlet air temperature fluctuation by 31.98% at the maximum under the continuous operation of different air volume systems for 7 days. At the same time, the cooling capacity can be increased by 19.89% at maximum compared with the conventional EAHE cooling capacity.

Performance analysis of building-integrated earth-air heat exchanger retrofitted with a supplementary water system for cooling-dominated climate in Taiwan

The thermal performance of a building-integrated earth-air heat exchanger (EAHE) retrofitted with a supplementary water piping system has been analyzed. The EAHE system has no excavation cost by integrating with the building foundation and gets better cooling performance by flowing supplementary water from residential water well to the foundation-integrated water-based EAHE (FIWEAHE) system. The experimental and numerical investigation was conducted to analyze the air conditioning performance of the FIWEAHE system. The simulated bulk temperature and humidity ratio of outlet air were validated with the year-round experimental data. After mixing with the circulating water from the residential water well, the cooling capacity of the FIWEAHE system enhanced from 3.21 kW to 4.84 kW, and its moisture removal rate soared from 1.97 kg/h to 4.24 kg/h during summer operation. The outlet air temperature varying from 24 to 26 °C in summer and 20–21 °C in winter can meet the standard of indoor thermal comfort. The mean COP of the FIWEAHE system during summer and winter operation is calculated as 10.5 and 1.74, respectively. Relation curves among air velocity and energy-efficient design of pipe geometry were developed to be the future design guideline of the FIWEAHE system.

Evaluation of the Cooling Potential of Earth Air Heat Exchanger Using Concrete Pipes

An earth air heat exchanger (EAHE) has advantages of its simplicity, easy implementation and low operating cost. The EAHE system is found less expensive for cooling and heating of buildings in severe climates. In this research paper, efforts have been made to analyze the accomplishment of a low-cost cooling system of outdoor air for the hot-dry & hot-humid climate. The effect of velocity, length and depth on the cooling potential of the system is studied at the inlet and outlet of the pipe. The novelty of this research is that enormous enhancement of the cooling potential has been observed in hot-humid climate than hot-dry climate, which is not available in previous studies. The results show that the maximum cooling potential in hot-dry climate is found 5643 kWh, 7375 kWh, 8939 kWh for the EAHE length of 15 m, 30 m and 45 m, respectively, corresponding to the velocity 2.5 m s−1 and depth 1.5 m. Whereas in a hot-humid climate, maximum cooling potential is achieved 13,373 kWh, 20,134 kWh and 24,080 kWh with a length of 15 m, 30 m and 45 m, respectively, for the given velocity and depth.