Earth Air Heat Exchanger Research Articles

Thermal Performance of Earth Air Heat Exchanger for Geothermal Energy Application in Hot Climate using CFD Simulation

The Ground Air Heat Exchanger (GAHE) is a sustainable, environment friendly, and efficient device that can be used for both heating and cooling applications. Careful design of GAHE enables efficient exploit of the earth interior energy. The design of a GAHE relies on the constant temperature of the earth interior which allows consistent and reliable source of geothermal energy. By harnessing this renewable energy, a sustainable solution for heating and cooling needs is attained while minimizing the impact on environment. In this study, the performance of GAHE was examined using ANSYS Fluent 19 R1 and SOLID WORK 16.0 software. The efficiency and Coefficient of Performance (COP) of the ETHE have been investigated. The effect of air flow rate and operation conditions on the outlet air temperature have been studied. GAHE is made of Polyvinyl Chloride (PVC) pipe of 0.1 m diameter, 0.005 m thickness and 18 m horizontal length. Computer simulations were carried out for five different air velocities (1, 2, 3, 4, and 5 m/s) at various operation conditions. Results show that the 18 m pipe length is adequate to attain useful air outlet temperature giving COP values between 0.5 and 1.3. The length of the horizontal part of GAHE can be further increased for air velocities between 3 and 5 m/s. Comparison between the results obtained by the CFD model and experimental work demonstrated that the CFD model is capable of producing results with acceptable accuracy. This suggests that the CFD software can accurately model the performance of the GAHE under different operation conditions. Increasing the length of the horizontal part of the GAHE can improve its COP when higher air velocities are used.

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.

Influence of different types of pipes on the heat exchange performance of an earth-air heat exchanger

An earth-air heat exchanger (EAHE) is a green technology suitable for regulating the thermal environment of buildings; however it requires a large space and high construction costs. In this study, five types of pipes, such as aluminum, stainless steel, polyvinyl chloride, corrugated, and perforated corrugated pipes were selected as the heat exchange pipes to study the effects of pipe material, roughness of pipe, and bottom perforation on the performance of the EAHE under short-time, intermittent, and continuous operation conditions, and to identify the most suitable EAHE pipe. The results showed that in the case of thinner wall thickness, the pipe material had a negligible effect on EAHE performance, with a preference for cheaper pipes. Compared to smooth pipes, corrugated and perforated corrugated pipes significantly improved the heat transfer performance and reduced the pipe length by 28.33–33.33% and 22.67–29.33%, respectively. Although perforations in the bottom of the pipe could increase the heat exchange between the air inside the pipe and the lower soil layer, accelerate the recovery of the soil temperature, and increase the cooling time, it significantly reduced the heat exchange efficiency. Thus, the corrugated pipe with the best overall performance indicated that a pipe with rough surfaces was the most suitable pipe type for EAHE. This can significantly lower the amount of space and money needed for EAHE construction, making it suitable for a variety of building types and contributing to the solution to the issue of rising global temperatures brought on by the use of conventional energy in the construction sector.

A review of earth contact heating/cooling systems and a comparison of ground source heat pumps and earth air heat exchangers

Countries should reduce greenhouse gas emissions and increase energy efficiency in alignment with the Paris Agreement and the European Green Deal. The adoption of environmentally friendly and low-energy systems, such as passive heating and cooling technologies, can significantly contribute to achieving this goal. The study covers the examination of new technologies ready for commercialization, economic developments to increase accessibility, scale-up of production to reduce costs, and notable case studies comparing ground source heat pump (GSHP) systems to solar building systems powered by earth-to-air heat exchangers (EAHE).

Enhancing real-time earth–air heat exchanger outlet temperature forecasting in arid climates using artificial neural network: a case study from Bechar, Algeria

Abstract This study improves earth–air heat exchanger (EAHE) outlet temperature forecasting using artificial neural networks (ANNs) to enhance building energy efficiency. Leveraging data from Bechar, Algeria, an arid climate, a FFBPNN with one hidden layer was trained, validated, and tested. Increasing the number of neurons in the hidden layer significantly improved model accuracy. The optimal architecture, with 40 hidden neurons, demonstrated high predictive accuracy, as shown by reduced MSE and increased R2 values across datasets. This research highlights the potential of ANN-based models to optimize EAHE system performance, contributing to energy-efficient building designs, particularly in arid regions.

Assessment of annual performance of quonset GiPVT system combined with an earth-air heat exchanger (EAHE) for hot and dry climatic conditions

Annual performance of a Quonset-shaped GiPVT system combined with an earth air heat exchanger (EAHE) has been evaluated for hot and dry climatic conditions. A periodic thermal model for the GiPVT system has been developed in terms of input climatic and design parameters by employing the energy balance equations of the greenhouse system. The present model is used to calculate the effective cooling and heating capacity of the EAHE, which is further utilized to determine the optimum operating hours of EAHE for different months of the year. Furthermore, the electrical energy of the GiPVT system and the thermal energy of EAHE are calculated, enabling a comprehensive performance evaluation of the greenhouse system. Results show that the EAHE increases the greenhouse air temperature by 8 °C on the coldest day and decreases the greenhouse air temperature by 21 °C on the hottest day of the year. EAHE has a lower potential for heating than cooling because of the hot and dry climatic conditions. Moreover, the system generates 17.6 kWh and 29.22 kWh of electrical energy on an extremely cold and hot day, respectively making the system self-sustainable. The EAHE significantly reduced TLL and DF values, which gives thermal comfort to the greenhouse.

Performance of an earth-air heat exchanger (EAHE) in a heat recovery ventilation for residential buildings in severe cold regions

The prolonged duration of winter season and the occurrence of extreme low temperatures present significant challenges when implementing mechanical ventilation systems in severe cold regions. These challenges encompass substantial requirements for heating supply air and frequent operations for defrosting. Heat stored in the ground has the potential to be harnessed for pre-conditioning supply air through the utilization of an earth-air heat exchanger (EAHE). This study focuses on evaluating the heating performance of the EAHE when integrated into a heat recovery ventilation system. The energy model of a case building in Harbin and the proposed ventilation system were simulated in IDA ICE. The results show that as the outdoor temperature drops, the proportion of heat supplied by EAHE increases, leading to a decrease in reliance on reheater to heat supply air. This underscores the advantages of applying EAHE to preheat fresh air in colder climates.

An Explorative Study of Earth-Air Heat Exchanger for Sustainable Building Applications

An Explorative Study of Earth-Air Heat Exchanger for Sustainable Building Applications

Evaluation of the earth-air heat exchanger's performance in improving the indoor conditions of an industrial poultry house using computational fluid dynamics verified with field tests

This paper aims to investigate the performance of an Earth Air Heat Exchanger (EAHE) to improve the indoor conditions of an industrial poultry building after its installation, considering the optimal position and installation configuration (separate or collected inlets), which have not been addressed previously. In this regard, an industrial broiler house containing 20,000 chickens equipped with four cooling pads operated by a mechanical ventilation system located in Biskra, Algeria, was simulated with six scenarios, including the original. The model developed is verified with the field test measurements and experimental and numerical data in the literature. The results showed that optimizing the cooling pad position increases average indoor air temperature and velocity distribution by 0.1% and 8%, respectively. Moreover, the position and configuration of installing the EAHE inlets play an important role in uniforming indoor air distribution. Scenario 3, with 80 EAHE inlets versus exhaust fans, has the best indoor air uniformity, with a maximum velocity and temperature difference between its sections of 1.15 m s−1 and 1.4 K, respectively. Overall, EAHE showed a good ability to cool and maintain appropriate indoor air temperatures, achieving a difference of 15 °C between inside and outside, in addition to providing annual energy savings of 921,600 kWh/year and reducing 30,643 tons of CO2 emissions during its lifespan, in contrast, its simple payback time estimated 4 years.

Optimizing Earth-Air Heat Exchangers for Sustainable Summer Cooling and Winter Heating

Optimizing Earth-Air Heat Exchangers for Sustainable Summer Cooling and Winter Heating

A numerical study on the performance of a hybrid ventilation and power generation system

Ventilation, cooling and power are essential requirements of buildings. Integration of solar chimney, earth-air heat exchanger and photovoltaic panel forms a new hybridsystem, which is able to provide simultaneous ventilation, cooling capacity and electricity in an effective manner for buildings. The contribution of this study is to quantitatively identify the thermal and electrical performances of the hybrid system using a comprehensive validated numerical model. In addition, a parametric study was also performed to examine the effect of the number of EAHE pipe and solar collector on the performance of the hybrid system in order to further enhance the system performance. The results revealed that the peak daytime ventilation of the proposed hybrid system is reduced by 22.05 % compared to the ventilation system of solar chimney integrated with earth-air heat exchanger, and the outlet air temperature is reduced by 0.12 °C in average; the indoor temperatures for the hybrid and ventilation systems are slightly different. Moreover, the minimum electrical efficiency of hybrid system is 1.34 % higher than that for stand-alone photovoltaic system. Increasing the number of earth-air heat exchangers leads to more than 36.43 % increase in peak ventilation volume and 3.7 % improvement in electrical efficiency. In addition, increasing the quantity of solar chimney-photovoltaic modules can effectively increase the induced ventilation volume, and the outlet air temperature, but has slight effect on the temperature and electrical efficiency of photovoltaic panel. Therefore, the hybrid system not only can supply appropriate ventilation but also can generate electric power to buildings. The findings provide a preliminary guidance for optimizing design of the hybrid system.

Design and analysis of earth-air heat exchanger integrated into the building ventilation system

This experimental study intent to design and to analyse the passive cooling effect of an Earth-Air Heat Exchanger (EAHE) integrated into the building ventilation system. For hot climate regions, ground thermal inertia can be used as a passive cooling strategy in the building ventilation where the air supply comes from outside with hot temperature. The proposed EAHE device consists of two main-components; a water tank and a PVC hose as a heat-exchanger between air and water in the tank. Fresh air from outside with a flow rate of 5.63 kg. min-1 is blown through a 2 ½-inch PVC hose, and cooled by the low water-soil temperature before being distributed into the room. To analyze the effectiveness of the passive cooling effect, measurements are performed for several parameters; inlet and outlet air temperature of ventilation ducts and indoor-outdoor air temperature using a multichannel thermocouple data logger for 48 hours of measurement time. The results present that the EAHE device can reduce the air temperature to a maximum of 10.6 °C. This proposed EAHE device presents good performance as a passive cooling technique for a building ventilation system, especially during the day.

A Large-Diameter Earth–Air Heat Exchanger (EAHX) Built for Standalone Office Room Cooling: Monitoring Results for Hot and Dry Summer Conditions

Earth–air heat exchangers (EAHX) use the soil thermal capacity to dampen the amplitude of outdoor air temperature oscillations. This effect can be used in hot and dry climates for room cooling, and depending on the EAHX design, this cooling can be achieved with very few resources other than those used during EAHX construction. This is an obvious advantage compared to the significant energy consumption and operational costs of refrigeration machines traditionally used in room cooling. Despite the large number of papers on EAHXs available in the scientific literature, very few deal with large-diameter EAHXs (with pipe diameters larger than 0.30 m), and even fewer present monitoring data gathered from a built and functional large-diameter EAHX. The present paper uses monitoring data and provides a detailed quantitative analysis of the performance of a large-diameter EAHX built for standalone cooling of an existing office building. The field monitoring was carried out during a characteristic hot and dry summer period of the south of Portugal. Results show that outdoor air to EAHX exit air temperature gradients reach 9 K and cooling capacities exceed 27 kW. Moreover, the studied EAHX is capable of standalone cooling for outdoor air temperatures up to 33 °C and meets more than 50% of the room design cooling demand for outdoor air temperatures as high as 37 °C. This evidences that large-diameter EAHXs have the potential to achieve significant reductions in CO2 emissions and in energy consumption associated with building cooling in hot and dry climates.

Computational fluid dynamics simulation of earth air heat exchanger combined with the Quonset type greenhouse to develop a sustainable controlled environment

The current study aims to evaluate the performance of an earth air heat exchanger (EAHE) combined with a Quonset-type greenhouse in a summer climate to create a controlled environment for optimum crop development and energy efficiency. The integrated systems thermal performance and airflow patterns are analyzed using computational fluid dynamics (CFD) models. The result shows that greenhouse room air can be satisfactorily achieved in the comfortable temperature range (27–37 ℃) for plant growth by combined EAHE even during the hottest summer days. EAHE reduces greenhouse temperature with a minimum temperature gradient of 17 °C between the ambient and air at the exit of EAHEs after the heat exchanging process. It is observed from the analysis that as the flow rate of air entering into EAHE increases, the greenhouse room's temperature decreases up to 0.5 kg/s; after that, there is no significant change in temperature, which makes 0.5 kg/s the recommended flow rate for the model used in the simulation. Pressure loss is reduced in a multi-pipe EAHE system compared to a single-pipe system. This advantage can increase energy efficiency and lower operating costs in greenhouse cooling. The Quonset GiTPV system generates 29.22 kWh of electrical energy daily, making it self-sustaining.

Investigation of heat transfer augmentation and friction factor in twisted tape-based earth-to-air-heat exchanger: a CFD-based analysis

Earth air heat exchangers (EAHES) are an innovative way to heat and cool buildings by utilising the earth’s natural temperature. Utilizing twisted tape (TT) as an enhancement technique in the EAHE can significantly boost heat transfer passively. This study employs CFD simulations (Ansys Fluent 2022) with SST turbulence model for a fixed Reynolds number range (20,000–52,000). The Twist Ratio (y/w), representing the number of turns of TT inserts, is a critical roughness parameter. The ground temperature across whole soil domain is held constant at 26.7°C. Numerical results are validated against available data showing a close match, particularly at the outlet temperature. Maximum decrement in temperature at exit of EAHE for smaller twist ratio(y/w) is 19.53% as compare from conventional (plain pipe) EAHE for cooling mode. Nusselt number increment of the current design is 50.41% more than the previous design with TT inserts of Re = 51344, number of turns(y/w) = 15, respectively and for friction factor the maximum increment is 2.253 times without TT inserts EAHE at Re = 20573 for 15 turns, respectively. The maximum thermal performance factor improves by 1.19 times with TT inserts in EAHE, achieved at 15 turns and a Reynolds number of 51,344. Abbreviations: EAHE: earth to air heat exchanger; TT: twisted tape; LES: Large Eddy Simulation; RANS: Reynolds-Averaged Navier-Stokes.

NUMERICAL ANALYSIS OF A VERTICAL HELICAL EARTH-AIR HEAT EXCHANGER

The Earth-Air Heat Exchanger (EAHE) is an equipment that consists of ducts buried in the ground in which the air is forced to pass through. The heat exchange with the surrounding soil turns the air temperature in the outlet section of the EAHE milder. Due to that, the EAHE is capable of assist air conditioning systems and reduce energy consumption, by taking advantage of the temperature gradient established between the soil surface and its layers. In the current study, the operation of Vertical Helical EAHEs was numerically evaluated with different distances between helicoid curves, for the city of Viamão, located in the southern Brazil. The results stated that the Vertical Helical EAHE with dimensions between the curves equivalent to 100 and 200 mm presented the better thermal performances for cooling mode operation in the hottest seasons of the years, when compared to the Conventional Horizontal EAHE adopted as reference. Frim this comparison, the obtained average values of the Root Mean Squared Error (RMSE) were, respectively, 0.47 °C and 0.66 °C. At last, it must be highlighted a sevenfold reduction in the soil volume occupied by the installation of the Helical EAHE compared to the Conventional Horizontal EAHE.

Experimental study on the characteristics of radiation floor cooling system based on an earth–air heat exchanger

Experimental study on the characteristics of radiation floor cooling system based on an earth–air heat exchanger

Development and evaluation of earth air heat exchanger cum evaporative cool system as an energy-efficient method for storage of tomatoes.

The lack of adequate on-farm storage facilities is one of the leading causes of enormous postharvest losses of fresh commodities, negatively affecting farmers' livelihoods and the sector's economic contribution. The aim of the current study was to develop and evaluate a solar-powered earth air heat exchanger cum evaporative cooling (EAHE-EC) system as an energy-efficient method for the storage of fresh produce for smallholders. The postharvest quality parameters of tomatoes stored under ambient storage (AS) and in an EAHE-EC system were assessed at regular time intervals during storage. These include weight loss, total soluble solids, titratable acidity, fruit firmness, color, pH, ascorbic acid, lycopene content, total phenolic acid, and antioxidant activity. The average temperature and relative humidity inside the EAHE-EC system varied from 20.59 to 22.61 °C and 82.60% to 89.43%, respectively, in comparison with AS (26.39-39.21 °C and 22.09-43.58%). Storage methods and time had a significant (P < 0.05) effect on tomato quality. Based on the retention of the overall quality until the end of the storage period, the shelf life of tomatoes was recorded as 21 days in the EAHE-EC system, which was 1.5 times more than AS (14 days). The extra shelf-life gained by tomatoes in the EAHE-EC system may provide a sufficient buffer period for smallholders for retailing and marketing. This suggests that the developed system can maintain postharvest quality and increase the shelf life of tomatoes. It therefore has potential as an energy-efficient system for the storage of fruits and vegetables, including tomatoes. © 2023 Society of Chemical Industry.

An Investigation of the Thermal Performance of a Tropical Greenhouse Constructed With an Earth Air Heat Exchanger

Abstract To maintain optimum plant growth temperature (i.e., 25–35 °C), the thermal performance of an earth air tunnel heat exchanger (EATHE)-integrated single-span saw-tooth greenhouse (GH) was assessed in peak summer. With the side and roof vents opened, natural ventilation due to wind and stack effect controlled the air movement and temperature inside the GH. In this configuration, the average temperature inside the GH remained higher than the ambient temperature by 1.5 °C for the entire period of the experiment. For EATHE (installed at a depth of 3.2 m) assisted GH with polyethylene (PE) cover, the air from the EATHE outlet entered inside the GH at 33 °C, and the average temperature within the GH was maintained at 4 °C lower than the ambient temperature. When the shading net was installed over the PE cover with the EATHE, the transmitted radiations into the GH were reduced from the roof, and the inside temperature was maintained 7 °C below the average ambient temperature (i.e., 45 °C). The measured temperatures along the length of the EATHE were compared with the indigenously developed code named PEAT (performance analysis of earth–air tunnel) and found to be in good agreement within ±4.5% deviation. The temperature distribution inside the GH was predicted using a computational fluid dynamics (CFD) model in ansys fluent with ±5% deviation from experimental results. With parametric analysis from the PEAT code and CFD model, the desired depth of the EATHE and the mass flowrate of air required to bring down the GH indoor temperatures to the optimum plant growth range were determined.

Modeling and optimization of integrated earth air heat exchanger and direct evaporative cooling system using ANN and RSM approaches for preserving fruits and vegetables

AbstractConventional air‐conditioned storage systems are more energy intensive which requires a consistent supply of electricity. Apart from this, it is costly and not suitable in remote areas where electricity is almost inaccessible. Therefore, the present study aimed to test the performance and feasibility of an integrated earth air heat exchanger and direct evaporative cooling system for storage of fruits and vegetables. The effects of air velocity (4–6 m/s), water flow rate (0.032–0.096 kg/s), and thickness of the cooling pad (50–150 mm) with corresponding responses were investigated in order to develop response surface methodology (RSM) and artificial neural network (ANN) models and compared them to predict temperature drop and humidity rise. Using RSM model, the optimum values for maximum temperature drop (16.80°C) and humidity rise (70.85%) within a range of input variables were found to be 4 m/s air velocity, 0.065 kg/s water flow rate, and 150 mm thickness of the cooling pad. For predicting the temperature drop and humidity rise, the higher (0.992 and 0.998) lower MAE (0.045 and 0.064), RMSE (0.187 and 0.266), and values (0.028 and 0.001) were observed in the ANN model. The developed ANN model was better than RSM models, and the model prediction was in good agreement with experiment values within the range of ±5% uncertainty. The results of this study indicate that the proposed cooling system can be successfully applied to store horticultural commodities.Practical ApplicationIntroduced hybrid cooling technique is low‐cost and eco‐friendly, and can be commercially used for on‐farm storage of fruits and vegetables to enhance their shelf life. The system is helpful for smallholder farmers/retailers to maintain the quality of the commodity during storage, minimize post‐harvest losses, and fetch good market value for the commodity.