Earth Air Heat Exchanger Systems Research Articles

Enhancing cooling performance and economic analysis of a vertical earth air heat exchanger (VEAHE) through geometric shape optimization

AbstractThe cooling and heating sector is responsible for the highest energy consumption in the building sector, comprising approximately 30% of the total. Extensive research has been conducted to address this issue and minimize energy consumption through the implementation of innovative technologies. Among these technologies, the passive earth‐air heat exchanger (EAHE) has proven highly effective in reducing energy usage in the cooling and heating sector. This research focused on optimizing U‐shaped EAHE systems and examined their functional and thermal‐fluidic parameters through numerical analysis. The simulation employed COMSOL Multiphysics software, and the results obtained were in excellent agreement with experimental data. The study investigated a base case, as well as five optimized cases with varying inlet velocities, to evaluate performance. The findings revealed that increasing the working fluid's inlet velocity led to a decrease in the system's thermal efficiency. However, at higher velocities, the economic parameters for energy production showed improvements. Specifically, the system generated a maximum energy output of 9132 W in the fifth case, operating at a velocity of 2 m/s. Additionally, the system achieved an impressive performance coefficient of approximately 5.13 in the same case, with an inlet velocity of 0.46 m/s. Notably, the lowest recorded output temperature of the system was 22°C at the specified inlet velocity.

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.

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).

A comprehensive review on experimental, numerical and optimization analysis of EAHE and GSHP systems.

Geothermal energy is one type of renewable source of energy that can be used as shallow geothermal system for the use of cooling and heating of residential and commercial buildings. In this paper, an intense review is carried out on geothermal heating and cooling for air conditioning with a focus on Earth-Air Heat Exchanger (EAHE) and Ground Source Heat Pump (GSHP) systems. The study is carried out to understand the factors which have a significant effect on the performance of the EAHE and GSHP systems. This paper also focuses on the hybrid work of geothermal heating and cooling system with other forms of energy and provides benefits for designing efficient GSHP and EAHE systems. This study indicates that the important parameters for EAHE and GSHP systems are the thermal conductivity of soil, the water content present in the ground will significantly improve the performance of the systems, and further benefits are discussed in this study.

Comparative energy, exergy, environmental, exergoeconomic, and enviroeconomic analysis of building integrated photovoltaic/thermal, earth-air heat exchanger, and hybrid systems

A comparative study is performed to assess a hybrid building integrated photovoltaic/thermal (BIPV/T) system and earth-air heat exchanger (EAHE) in comparison with individual BIPV/T and EAHE systems. Different systems are examined based on energy, exergy, environmental, exergoeconomic , and enviroeconomic analysis. The hybrid system is able to increase/decrease the outdoor air temperature in winter/summer and produce electricity. A parametric study is also performed to inspect the impact of geometrical and operational metrics on the exergoeconomic and enviroeconomic parameters of the hybrid system. The outcomes revealed that the hybrid device produces higher annual total thermal and electrical energies by almost 10.1% and 935.6% compared with the BIPV/T and EAHE systems, respectively. In addition, it was found that the hybrid system produces 3.2% less annual total thermal and electrical exergy compared with the BIPV/T unit. While the hybrid system's enviroeconomic parameter was 3.2% less than the BIPV/T unit, its exergoeconomic parameter was 51% higher than that for the BIPV/T system. The case study analysis indicated that the exergoeconomic parameter increases by enhancing the air mass flow rate and EAHE length. Furthermore, it was found that the enviroeconomic parameter increases for a higher length and width of the BIPV/T system. • 5E analysis of hybrid BIPV/T-EAHE system compared with the individual systems. • Performing a case study to evaluate the effective parameters on the hybrid unit. • 10.1% and 935.6% higher annual useful energy compared with BIPV/T and EAHE systems. • Higher exergoeconomic parameter by 51% compared with the BIPV/T system. • Lower enviroeconomic parameter by 3.2% compared with the BIPV/T system.

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.

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.

Performance evaluation of a novel hybrid cooling system combining indirect evaporative cooler and earth-air heat exchanger

In this research, a new hybrid system combining indirect evaporative cooler and underground air tunnels has been proposed as an eco-friendly alternative for vapor-compression cooling cycles. Indirect evaporative cooling is an efficient thermal comfort cooling method in arid and semi-arid climates. Due to global warming and limited water resources, managing and monitoring of water consumption in evaporative coolers are of particular importance in these regions. In the present study, the cooling efficiency and water consumption of the proposed novel hybrid system are evaluated theoretically. To this aim, a mathematical model was developed for simulating the cooling performance of indirect evaporative cooler and earth-air heat exchanger systems. The fully implicit finite difference scheme was employed in computations. The simulations were validated against some available experimental and numerical data and a good agreement was obtained. The effect of the design parameters of the underground pipe on pre-cooling performance was studied. The results showed that coupling the underground heat exchanger to an indirect evaporative cooler not only improved cooling performance but also significantly decreased water consumption. Besides maintaining the desired thermal comfort level, our investigation indicated that the proposed system can decrease energy and water consumption by about 62% and 45%, respectively.

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.

Numerical study of a new earth-air heat exchanger configuration designed for Sahara climates

Thermal performance for cooling and heating in the building can be achieved by the novel shape of the earth–air heat exchanger (EAHE). In a heavily populated area such as City, Due to the limited ground space. EAHE systems are rarely used, for most residential andcommercial utilization.This paper presents a numerical investigation of the thermal performance of a spiral-shaped configuration Spiral Earth to Air Heat Exchanger SEAHE intended for the summer cooling inhot and arid regions of Algeria. A parametric analysis of the SEAHE has been performed toinvestigate the effect of diameter, depth, pipe length and of airflow rate on the outlet air in theexchanger. Results show that the specific heat exchange is used to cool in an arid zone (south-east of Algeria). When the ambient temperature varies between 40°C and 45 °C, the coolingtemperature varies between 25°C and 29 °C. Temperature difference inlet and outlet airexchanger 18°C, these values are quite acceptable with for cooling the building.

On Preheating of the Outdoor Ventilation Air

The growing popularity of buildings with integrated sub-systems requires a review of methods to optimize the preheating of ventilation air. An integrated system permits using geothermal heat storage parallel to the direct outdoor air intake with additional treatment in the mechanical room as a part of building an automatic control system. The earth–air heat exchanger (EAHX) has many advantages but also has many unanswered questions. Some of the drawbacks are: A possible entry of radon gas, high humidity in the shoulder seasons, and the need for two different air intake sources with a choice that depends on the actual weather conditions. In winter the EAHX may be used continuously to ensure thermal comfort, while in other seasons its operation must be automatically controlled. To generate missing information about EAHX technology we examined two nearly identical EAHX systems, one placed in the ground next to a building and the other under the basement slab. In another project, we reinforced the ground storage action by having a heat exchanger placed on the return pipes of the hydronic heating system. The information provided in this paper shows advantages of merging both these approaches, while the EAHX could be placed under the house or near the basement foundation that is using an exterior basement insulation.

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.

Thermal and infrared camouflage performance of earth-air heat exchanger for cooling an underground diesel generator room for protective engineering

Research on earth-air heat exchanger (EAHE) systems focuses on their energy efficiency for civil and industrial buildings. For cooling the protective engineering’s diesel generator room, outlet temperature of EAHE system should be controlled within a certain range close to the outdoor temperature to avoid infrared exposure to military reconnaissance. This study proposed a cooling method for the protective engineering’s diesel generator room by using the engineering’s tunnel as a EAHE. At the beginning, recommended velocity was proposed to meet the infrared camouflage requirement. In addition, influencing parameters including the heat generated in the diesel generator room, soil temperature, and average value and magnitude of outdoor temperature are studied. Also, 3 intermittent modes are simulated. For all simulations, both the cooling capacity and the infrared-camouflage-guaranteed duration are compared. Results show that this system is suitable for small-scale engineering with high average outdoor temperatures and low temperature difference between day and night. The intermittent ventilation significantly improved the infrared camouflage effect while it works but not the total cooling capacity because of the shorter working hours. The infrared-camouflage-protection duration increased by 29.96% as the system intermitted every 9 h, compared with that under non-intermittent ventilation condition.

Thermal Modeling of a Rooftop Photovoltaic/Thermal System With Earth Air Heat Exchanger for Combined Power and Space Heating

Earth air heat exchanger (EAHE) systems are inefficient to provide thermal comfort in winter season for semi-arid regions. The performance of such systems could be improved by coupling them with other renewable energy sources. One of the renewable energy technology is rooftop photovoltaic/thermal (PV/T) air collectors which could utilize the incident solar insolation to obtain both electricity as well as useful heat. In the current paper, the thermal performance of an EAHE coupled with a PV/T system has been numerically investigated for climatic conditions of Pilani, Ajmer (India), and Las Vegas (U.S.). For the comparative analysis, a thermodynamic model has been developed and compared with experimental data available in the literature which seems to be in good comparison with the results. Further, a parametric analysis has been carried out for assessing the effect of different operating parameters. Results showed that for the winter season, the maximum cell temperature without any cooling goes up to 54.3 °C, 54.5 °C, and 44.4 °C for Pilani, Ajmer, and Las Vegas, respectively, while with cooling it drops to 43.4 °C, 44.2 °C, and 35.6 °C, respectively, for 0.053 kg/s flow rate. The heating capacity of the EAHE was observed to be improved with PV/T air collector by 23.47 Wh–298.74 Wh, 71.18 Wh–315.93 Wh, and 41.43 Wh–270.75 Wh for the Pilani, Ajmer, and Las Vegas, respectively.

Working parameters affecting earth-air heat exchanger (EAHE) system performance for passive cooling: A review

The study on the effect of the working parameters such as pipe material, pipe length, pipe diameter, depth of burial of the pipe, air flow rate and different types of soils on the thermal performance of earth-air heat exchanger (EAHE) systems is very crucial to ensure that thermal comfort can be achieved. In the past decade, researchers have performed studies to develop numerical models for analysis of EAHE systems. Until recently, two-dimensional models replaced the numerical models in the 1990s and in recent times, more advanced analysis using three-dimensional models, specifically the Computational Fluid Dynamics (CFD) simulation in the analysis of EAHE system. This paper reviews previous models used to analyse the EAHE system and working parameters that affects the earth-air heat exchanger (EAHE) thermal performance as of February 2017. Recent findings on the parameters affecting EAHE performance are also presented and discussed. As a conclusion, with the advent of CFD methods, investigational work have geared up to modelling and simulation work as it saves time and cost. Comprehension of the EAHE working parameters and its effect on system performance is largely established. However, the study on type of soil and its characteristics on the performance of EAHEs systems are surprisingly barren. Therefore, future studies should focus on the effect of soil characteristics such as moisture content, density of soil, and type of soil on the thermal performance of EAHEs system.

Parametric simulation and experimental analysis of earth air heat exchanger with solar air heating duct

Earth air heat exchanger (EAHE) systems are insufficient to meet the thermal comfort requirements in winter conditions. The low heating potential of such systems can be improved by integrating the system with solar air heating duct (SAHD). The aim of this paper is to present a model to estimate the heating potential for EAHE system with and without SAHD. The model is generated using TRNSYS 17 simulation tool and validated against experimental investigation on an experimental set-up in Ajmer, India. The experiment was done during the winter season, where the system was evaluated for different inlet flow velocities, length and depth of buried pipe. From the experimentation, it was observed that the depth of 3.7 m is sufficient for pipe burial and the 34 m length of pipe is sufficient to get optimum EAHE outlet temperature. It is also observed that increase in flow velocity results in drop in EAHE outlet temperature, while room temperature is found to increase for higher velocities (5 m/s). The COP of the system also increased up to 6.304 when assisted with solar air heating duct. The results obtained from the experiment data are in good agreement with simulated results within the variation of up to 7.9%.

Study on Calculation Models of Earth-Air Heat Exchanger Systems

Modeling is very useful tool in order to predict the effect of the operating parameters like pipe length, radius, depth of burial and air flow rate on the thermal performance and heating/cooling capacity of earth-air heat exchanger (EAHE) systems. Till date many researchers have carried out a number of studies on calculation models for earth-air heat exchanger systems. The analysis of EAHE systems started with the development of one-dimensional models. The two-dimensional models came into practice during the 1990s and were replaced by three-dimensional models in recent years. Latest models are dynamic and technically more advanced which can provide room for all types of grid geometry to produce detailed thermal analysis of EAHE systems. This paper reviews on calculation models of EAHE systems as of the end of March, 2014.