Air Heat Exchanger System Research Articles

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.

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.

A study on flow distribution characteristics of heat exchanger module integration scheme for aircraft environmental control system based on CFD

With the rapid development of the civil aviation industry, the performance requirements of the environmental control system for domestic commercial large aircraft are gradually improved, and the ram air inlet heat exchanger system is its main component. Generally speaking, a ram air heat exchanger system mainly includes an air conditioning system heat exchanger, air preparation system heat exchanger, and auxiliary cooling system heat exchanger. The integration mode of the heat exchanger will directly affect the flow and flow distribution characteristics of the ram air heat exchanger system. This paper develops three integration schemes referring to the integration mode of heat exchangers in Boeing 787 and Airbus 350 aircraft. Based on Fluent software, the calculation and simulation of three integrated scheme models under the seven working conditions of taking off, climbing, cruising, descent, hovering, emergency, and landing during flight were carried out, and the flow distribution and flow resistance values of different schemes were obtained, which were compared to meet the heat transfer requirements.

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.

Energetic and Exergetic Analyses of an Experimental Earth–Air Heat Exchanger in the Northeast of France

Earth–air heat exchanger (EAHE) systems are used to pre-heat or pre-cool air before entering into a building using shallow geothermal energy. Assessment of EAHE systems is important to quantify the profitability of these systems. For this purpose, an EAHE system built at ICUBE at the University of Strasbourg in the northeast of France was studied using energy and exergy analyses for a typical heating period (between 25 February and 3 March). Energy analysis was used to determine the heat gained by the air in the system during the studied period and to determine the Coefficient Of Performance (COP) of the system. Additionally, exergy analysis, which considered temperature, pressure, humidity, and the variation in the control volume boundary temperature, was realized to determine inefficiencies in the system by determining the exergy destroyed in each component of the system and evaluating its exergetic efficiency. Results showed that the heat energy gained using the system was around 63 kWh and that the exergetic efficiency of the system was about 57% on average. The comparison of exergetic efficiency between the EAHE components showed that the fan has the lowest performance and should be improved to achieve better overall performance.

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 Direct-Contact Gravel, Ground, Air Heat Exchanger—Application in Single-Family Residential Passive Buildings

This paper presents proposals for using the direct-contact gravel, ground, air heat exchanger in single-family residential buildings with a passive house standard, according to the Passive House Institute (PHI). The methodology of their application consists of using heat and cold from the ground at an insignificant depth (about 1.5–4.0 m below the ground level for the central European climate) through an aggregate that is buried in the ground. This solution of simple installations is used for preheating and cooling fresh air drawn into the building through a mechanical ventilation system with heat recovery. In more complex applications it can be integrated with the source of heat and cold in passive buildings to create complete heating, cooling, and ventilation systems. In both cases, the air flowing through the exchanger is cooled and dried in summer, heated and humidified in winter, and filtered from pollen and bacteria all year. Direct contact of the deposit with the surrounding native soil facilitates rapid regeneration of the bed temperature. This article presents several proposals for integration with systems ensuring climatic comfort in a passive building, as exemplary applications. The paper presents preliminary estimates of energy (savings of up to 70% of electrical energy consumed), economic (SPBT = 3.65 years), and environmental (69.5% reduction in CO2 emissions) benefits related to implementing this solution in various configurations of technological systems for buildings in Poland. The calculations were carried out for the city of Poznań, taking into account the hourly intervals and using the author’s code written in MS Excel. The analysis of the operation of the direct-contact gravel, ground, air heat exchanger (GGAHE) system is based on a theoretical heat and mass exchange model. The integrated solutions of technical systems presented in this article provide an interesting alternative to traditional heating, cooling, and ventilation systems.

Comparative study of the thermal performance of an earth air heat exchanger and seasonal storage systems: Experimental validation of Artificial Neural Networks model

This article presents a comparative study between two different geothermal systems: an earth air heat exchanger (EAHE) and seasonal storage systems. The energy efficiency of a combined geothermal system composed of two series of connected underground tanks coupled with a cooling floor and a PVC earth-air heat exchanger coupled to an experimental cell is presented through an experimental and numerical analysis. A measurement system is installed to study the thermal performance of both systems under the same conditions. The climatic conditions, the temperature at the outlet of the two systems were measured. This experimental protocol allows to evaluate and understand the interest of each system for cooling needs. Experimental results show that the energy performance of two systems is different. The blowing temperature of the EAHE varies between 19 and 24 °C, however the outlet temperature of the underground tank varies between 16 °C and 20 °C. Based on experimental data, a Long-Short-Term-Memory (LSTM) neural network algorithm is then used to forecast the underground tank and EAHE temperatures evolutions. The forecasting accuracy of the proposed model was evaluated using different statistical measures. The determination coefficient (R2), the Root Means Square Error (RMSE), and the Mean Squared Error (MSE) for the EAHE outlet temperature are 0.953, 0.093 and 0.306, respectively. Furthermore, the R2, MSE and RMSE for the underground tank temperature are 0.984, 0.165 and 0.406 respectively.

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.

Simulation Modeling for Earth to Air Heat Exchanger system by Using MATLAB

A MATLAB model was built for the preparation of initial designs for the establishment of an EAHE system for the purpose of heating and cooling buildings. The purpose of creating this model is to save time and effort by creating a new model capable of providing us and specialized designers with initial perceptions of the size of the appropriate system for the functional requirements for the purpose of cooling and heating buildings. A parametric analysis was then performed to evaluate and investigate the factors affecting the efficiency of the EAHE system. It was found that the pipe diameter is directly proportional to the pipe length, and inversely to the airflow velocity, pressure losses, and AFP. Airflow velocity reduced from 77.05 m/s to 0.1926 m/s, and AFP decreased from 9223 W to 0.058 W when diameter increased from 0.1 m to 2 m. The inlet air temperature affects the length of the pipe in four phases, it is inversely proportional in the first and third phases and directly in the second and fourth phases. These phases depend on the values of soil, inlet, and outlet temperature. This paper presents new equations to determine these phases to determine excluded range which is recommended should not use an inlet air temperature value through this range. The pipe number is directly proportional to pipe length. Pipe length increased from 57.16 m to 344.9 m when the pipe number increased from 1 to 10 pipes. The number of pipes has no influence on the overall airflow velocity or total heat transfer. The length of the pipe is directly proportional to the soil temperature in the first and third phases and inversely proportional in the second and fourth phases. Designers could get an idea of this range by utilizing the equations presented in this paper. There is no direct effect between the soil temperature and power, but rather it affects it through the length of the pipe, as it is directly proportional to pipe length.

Experimental evaluation of an earth–to–air heat exchanger and air source heat pump hybrid indoor air conditioning system

Earth-to-air heat exchanger (EAHE) technology is promising for space heating/cooling. However, in most climates, EAHE alone cannot provide indoor thermal comfort. Hybrid systems combining an EAHE and an air-source heat pump (ASHP) can be used for indoor temperature regulation and energy conservation. We performed full-scale experiments to investigate the hybrid system performance for a building located in a typical hot-summer and cold-winter region of China. Variations in EAHE outlet/indoor air temperature, humidity, cooling/heating loads, energy consumption, and coefficient of performance (COP) were investigated. The results demonstrate a maximum reduction of 14.2 °C during summers and maximum gain of 8.2 °C during winters for the EAHE outlet air temperature, when the air-change rate per hour reaches 16.0. Moreover, the EAHE dehumidifies 1.95 g/kg moisture on average in summer, approximately accounting for 36.2 % of the dehumidification capacity of the hybrid system, with more dehumidification capability for high moisture contents. Compared with an independent ASHP for specific ambient air temperature and humidity ranges, the proposed system exhibits an average energy consumption reduction of 50.91 % and 16.78 %, increases COPASHP by 65.42 % and 11.21 %, and increases COPt by 145.37 % and 82.63 % during the summer and winter periods, respectively.

Numerical Investigation of The Air Flow Rate Effect Performance of Earth to Air Heat Exchanger Used for Cooling of Poultry Houses

Usually, poultry houses are located in a remote area where there is no electricity, and where there is electricity, it is expensive, so resorting to these solutions is considered important solutions to save electrical energy and provide free cooling. The main part of generated energy is consumed by cooling and heating systems. One of the well-known approaches to implemented heating and cooling system is earth to air heat exchanger (EAHE) system. This system is effective passive heating and cooling systems which can be used with poultry houses and building. This research studies numerically the effect of mass flow rate on the overall performance of earth to air HE for poultry houses. Four parameters (mass flow rate, required rate, required cooling load and pipe lengths) are selected under environment of Nasiriyah city (a city located in the south of Iraq). The study is conducted using PVC material. The study has been done during summer season. The suggested numerical model has been tested and validated using existing approaches selected from literature review papers. This test shows good agreement with results of selected papers. Moreover, validation and simulation results showed that the required cooling load increased with increasing mass flow rate. Also, with the increasing length of pipe of EAHE, the inflow temperature compared to the space temperature is decreased. However, the overall performance factor of EAHEs decreases by the increase of length of pipe and mass flow rate. Which indicate the possibility of using the earth to air heat exchanger for cooling and heating poultry houses and reduce the use of electrical energy.

Forced and natural ventilation of a room with a combined solar chimney and Earth - to - Air Heat Exchanger system

In this study, a passive ventilation and cooling technique which is widely used in sustainable building designs was investigated by a numerical simulation based on computational fluid dynamics (CFD). A system of a solar chimney (SC) and an Earth-to-Air Heat Exchanger (EAHE) is able to ensure thermal comfort in a house by generating an air flow which is induced by the thermal effect. The solar chimney drew ambient air (at 35°C) through the inlet of EAHE; the air flow was cooled by a lower temperature of the underground pipes (at 20°C) before circulating inside the house and leaving through the outlet of the solar chimney. Both the openings of the system were exposed to the atmosphere, and the atmospheric pressure was set at the inlet of the EAHE pipe and the outlet of the solar chimney. The performance of this ventilation and cooling system was analyzed under effects of design parameters, including the gap of the chimney, the diameter and length of the EAHE pipe as well as the solar heat flux applied on the wall of the air channel of the chimney. The results of the assessed parameters, such as temperature inside the house, show that the indoor temperature was reduced to 25°C and 26°C, respectively for the forced ventilation case of 0.2 m/s and natural ventilation case in the configuration with the EAHE pipe length of 11m. The coupled solar chimney and EAHE system can achieve the thermal comfort conditions for both cases of natural and forced ventilation.

Procena iskorišćenja izmenjivača toplote vazduh-zemlja za pasivno hlađenje u tri regiona Alžira - studija slučaja

The energy consumption in buildings for heating and cooling continues to increase from year to year, in order to meet people's increased demand for thermal comfort. A key energy issue for the buildings sector, the largest consumer of energy, requires the rational use of traditional resources and the application of non-polluting, inexhaustible renewable energy technologies that allow sustainable development. The public authorities are currently showing a clear desire to reduce energy consumption in the buildings sector through various legislated thermal regulations. In Algeria, law 99-09 and executive decree 2000-09, followed by other regulations, have as objectives the control of energy and the introduction of energy efficiency in buildings. In this paper, we focused on the effectiveness of the earth-to-air heat exchanger system for cooling buildings in three different climate regions in Algeria. The Earth to air heat exchanger device is a promising technology for reducing or avoiding the use of air conditioning systems. The Earth to air heat exchanger system which exploits the thermal inertia of the soil puts two different temperature sources in thermal contact, the air which circulates in the tubes, and the ground placed in contact with the tubes. This model was validated to show a good agreement between simulated results and other experimental data published. The simulation results confirmed that A maximum energy gain of 2221.15 kWh, 523.56 kWh and 300.27 kWh over a cooling season can be reached for Timimoun, Djelfa, and Jijel.

A novel solar-geothermal system integrated with earth–to–air heat exchanger and solar air heater with phase change material—numerical modelling, experimental calibration and parametrical analysis

In order to compensate drawbacks of traditional earth–to–air heat exchanger (EAHE) system, such as the unstable outlet air temperature, the overheating and the limited operation period, a novel coupled system systematically integrating an EAHE and a solar air heater (SAH) with phase change material (PCM), was proposed in this study. The complementary between geothermal and solar energy is exploited and served for building energy savings. On-site experimental testing and enthalpy-based numerical modelling using the control volume method were conducted for thermal and energy performances prediction. Systematic and parametrical analyses have been conducted using the developed mathematical model to investigate the effects of critical parameters on the thermal and energy performances. Our findings illustrate that the implementation of PCM can effectively stabilize the outlet air temperature for nearly 4.5 h and prolong the working period to 24 h. Due to the heat transfer enhancement, the increase of the airflow rate can significantly increase the system heating capacity, whereas the outlet air temperature is decreased with a maximum magnitude of 5.3 °C. Furthermore, the diurnal thermal performance of the system is highly dependent on the phase change temperature, whereas the time-duration of the effective operation is highly dependent on the PCM latent heat. Moreover, the system nocturnal thermal behavior can be improved with the increase of the PCM thermal conductivity, whereas a saturated improvement can be noticed when the PCM thermal conductivity is 1.0 W/(m·K). This study proposes a complementary geothermal and solar energy system, together with phase change material for the performance stability improvement, which are important for the promotion of green buildings with energy-efficient utilization of geothermal and solar energy.

Comparative analysis of earth to air heat exchanger configurations based on uniformity and thermal performance

The multi-pipe earth to air heat exchanger (MEAHE) system is widely applied in the agricultural greenhouse for energy savings. The non-uniform airflow acts significantly on the overall performance, and the objective of the paper aims to investigate the influence of airflow uniformity on thermal performance. A mathematical model of the multi-pipe earth air heat exchanger was established with the CFD method, and the simulation results were validated by the experimental data in the literature. The uniformity and thermal performance of the multi-pipe earth to air heat exchanger were first investigated, and then the non-uniform airflow division under the different supply types was compared. Finally, the effect of main pipes diameter to parallel pipes diameter ratio on the thermal performance of earth to air heat exchanger was investigated. The study acknowledges that the heat transfer rate between soil and air of Z-type earth to air heat exchanger decreased by 10.7% than the uniform type earth to air heat exchanger. The study also revealed that the airflow and thermal uniformity of U-type and L-type was much better than Z-type earth to air heat exchanger. There are optimum main pipes diameter to parallel pipes diameter ratio with consideration of thermal performance and pressure drop. The results could be considered as the reference for the development and optimization of the earth to air heat exchanger in the greenhouse during the practical engineering.

Seasonal sensitivity to atmospheric and ground surface temperature changes of an open earth-air heat exchanger in Canadian climates

Open earth-air heat exchangers (EAHE) have an inherent relationship with their surrounding environment, relying on the natural contrast between ambient air and subsurface temperatures. This work explored the seasonal sensitivity of open earth air heat exchanger systems to variations in these temperatures. Utilizing 492 weather files in Canada, the heating and cooling potential of open earth air heat exchangers computed using a climate-based approach were compared for different seasonal variation scenarios. Heightened sensitivity to seasonal changes in ground temperatures relative to air temperatures were observed. These effects expectedly decreased with depth. Heating and cooling potential sensitivity to seasonal variations in air temperatures are dependent on the timing, often observing the greatest influence during peak demand periods. Binning by climates identified that regions with a greater mix of heating and cooling potential were more susceptible to seasonal variations. These results also suggest improvements to the heating potential in Canada can be improved by increasing ground surface temperatures outside the summer season, with little influence on the cooling potential. Understanding the interaction between open earth air heat exchanger systems and their environments can ultimately help outline limitations and design solutions specific to their implementation in Canadian climates.

Experimental and numerical analysis of soil - to - air heat exchanger system for domestic buildings

Experimental and numerical analysis of soil - to - air heat exchanger system for domestic buildings

Experimental Analysis of Effect of Soil Moisture on Thermal Performance of Earth Air Heat Exchanger

Earth Air Heat Exchanger (EAHX) systems are renewable energy systems based on the use of the high energy potential of the soil. Although it has a simple structure, there are multiple parameters that affect thermal performance. These parameters should be taken into consideration when installing the EAHX, which consists of a buried pipe system and a fan. In this study, the effect of humidification of the soil on which EAHX is placed by placing an irrigation line on thermal performance was investigated. In this study, two EAHX with the different material piping systems are discussed. In the study carried out at different airspeeds, inlet-outlet air temperatures, water temperature and air humidity were measured. It was determined that the decrease in the outlet temperatures of the systems using PVC and metal pipes was 10% compared to the dry condition. As a result of the study, it has been observed that moistening the soil increases EAHX efficiency. When the increase in cooling capacity and the additional cost caused by the irrigation system are compared, it is seen that the installation of soil humidification system is applicable in terms of energy efficiency.