Earth-to-air Heat Exchanger Research Articles

Experimental investigation on the cooling performance of an Earth to Air Heat Exchanger (EAHE) equipped with an irrigation system to adjust soil moisture

Earth to Air Heat Exchangers (EAHEs) are reliable complements for conventional HVAC systems. During summer, EAHE cooling can help reduce energy consumption. In the present study, to evaluate the cooling performance of a two-layer EAHE ventilating system, experimental work was conducted from May to August 2017. Because EAHE performance largely depends on the thermal characteristics of soil, an irrigation system was adopted to experimentally verify the effect of soil moisture content. Air temperature showed an average drop of 14.6 °C and the average total cooling capacity was 8792 W. The system exhibited a maximum coefficient of performance (COP) of 27.2, implying that the system provides fresh-air cooling with little electricity input. Under cooling mode, the surrounding soil temperature increased continuously due to the operation of the system. An irrigation system was adopted to simulate natural precipitation; when the soil moisture changed from 0.37 cm3/cm3 to 0.42 cm3/cm3, air temperature decreased by 1.6 °C at the pipe outlet. The results show that using EAHE under wet conditions resulted in a large cooling capacity and COP, which indicates that a short pipe length or shallow depth is required for achieving a similar cooling capacity under wet soil conditions.

Parametric study on the performance of the earth‐to‐air heat exchanger for cooling and heating applications

AbstractTo reduce energy consumption, the earth‐to‐air heat exchanger (EAHE) is a suitable technique for cooling and heating buildings. This paper studies numerically the effect of some design parameters (pipe diameter, inlet condition, pipe length, and outlet condition) on the overall performance of the EAHE system. Four diameters of the EAHE pipe (2, 3, 4, and 6 in) are studied and this numerical study has been done for summer and winter seasons for Nasiriyah city in southern Iraq. First, the built numerical model was validated against the experimental model, and the results of comparison showed a good consensus. After the validation and by using computational fluid dynamics modeling, the overall performance of the EAHE system with all pipe diameters was analyzed with ranges of air velocity, DBT or inlet temperature, and a pipe length of 50 m. The simulated results showed that the EAHE system with 6 in pipe diameter has the best values of overall performance, but from the thermal performance point of view, the 2 in pipe diameter is more suitable.

Experimental and numerical study of a vertical earth-to-air heat exchanger system integrated with annular phase change material

Vertical earth-to-air heat exchanger (VEAHE) systems have smaller land occupation and more efficient usage of geothermal energy than conventional earth-to-air heat exchanger (EAHE) systems. However, a large fluctuation in its outlet air temperature subject to ambient air temperature variations may occur, preventing it from meeting the indoor thermal comfort requirements. To address this issue, a novel VEAHE system integrated with annular phase change material (PCM) was proposed. The PCM can reduce the outlet air temperature fluctuation due to its ability to store and release energy. To evaluate its thermal performance, a numerical model was developed and validated by experimental data. The results showed a good agreement between the simulated and monitored data, with a maximum absolute relative error of 1.59% and 1.34% for the outlet air and PCM temperature, respectively. Then the validated model was applied to investigate the effects of PCM and its parameters on the system's thermal performance. Results showed that the annular PCM can decrease the outlet air temperature fluctuation of the system without PCM by 31% and 29% under air velocities of 1 m/s and 2 m/s respectively, enabling more stable outlet air temperatures to be achieved. The effect of PCM thermal conductivity depended heavily on the PCM thickness. Improving the system's thermal performance by simply increasing PCM thermal conductivity may not be an effective method, particularly when the PCM thickness was relatively small. As the PCM thickness exceeded 5 mm, an increase in the PCM thickness had a relatively small effect on the variation of outlet air temperatures. The outlet air temperature range decreased with the increase of PCM lengths, while a downward trend in the fluctuation decrease can be observed. In addition, an economic analysis of the proposed system was conducted, indicating that its static payback period was 20.8 years.

Designing and evaluating a new earth-to-air heat exchanger system in hot summer and cold winter areas

Energy demand for space cooling and heating in buildings is a primary contributor to the total building energy consumption. Its rapid increase calls for an urgent need to utilize renewable energy sources and associated energy-efficient technology in the building sector. Among different renewables, geothermal energy has been widely adopted due to its easy access and low impact on the environment. In this study, a new earth-to-air heat exchanger (EAHE) system with vertically buried tubes was proposed. Compared to the conventional EAHE systems, its advantages mainly include high geothermal energy utilization efficiency and ease of condensate water discharge. To evaluate the thermal performance and cooling capacity of this system, an experimental set-up was established and a series of tests were conducted in Hunan, China. The results show that the outlet air temperature of this system ranged from 22.4℃ to 24.2℃ as the air flow velocity set at 1.0 m/s, enabling it to be used as an energy efficient technology for summer cooling of buildings. Meanwhile, both inlet air temperature and air flow velocities have an important influence on the system’s cooling capacity.

Energy and thermal analysis of an innovative earth-to-air heat exchanger: Experimental investigations

Building integrated geothermal foundations are earth-to-air heat exchanger (EAHE) that offer alternative to numerous technical problems inherent to the traditional EAHE. However, an accurate understanding of their thermal behavior is crucial to ensure the best energy gain and an economic viability of this system. The study is based on experimental results obtained on a full-scale ventilated foundation. An accurate and global energy analysis relies on a detailed instrumentation and a one-year monitoring campaign. They focus on power, daily energy gains, surface energy gains, coefficient of performance, operation time and temperature dampening indicators. The results show that this system is very efficient for cooling, especially when compared to traditional EAHE. This performance is almost exclusively due to the contribution of the first half of the foundation length. The performance is satisfying in heating mode but could be improved using a simple on/off control of the airflow. An indicator is also proposed to understand the source of the heating / cooling fluxes.

A demand-oriented approach for integrating earth-to-air heat exchangers into buildings for achieving year-round indoor thermal comfort

Earth-to-air heat exchanger (EAHE) is a promising energy-efficient technology for indoor thermal environment regulation; however, it should adapt to both building and climatic conditions. This paper proposes a new inverse approach to determine the parameters of EAHE integrating into buildings and to achieve a prescribed indoor thermal comfort objective. First, the criterion for achieving year-round thermally comfortable indoor air temperatures is formulated. According to the objective, the required combined parameters characterizing the dynamic behavior of the earth-to-air heat exchanger outlet-air temperature are inversely calculated. Then, the earth-to-air heat exchanger parameters, such as length, radius, burial depth and flow rate, satisfying the proposed objective are determined. The results demonstrate that decreasing the phase shift of the anticipated indoor air temperature profile helps to reduce the requirements on earth-to-air heat exchanger parameters. A Computational Fluid Dynamics simulation incorporated with real meteorological date is implemented according to the EAHE parameters obtained from the proposed approach. It is demonstrated the proposed inverse approach is effective and the year-round indoor thermal comfort is achievable.

Performance of PV panel coupled with geothermal air cooling system subjected to hot climatic

A novel alternative cooling system for photovoltaic (PV) panels that includes passing pre-cooled ambient air over back panel surface is experimentally investigated for local conditions of Port Said, Egypt. This is an alternative cooling system in the sense that an earth-to-air heat exchanger (EAHE) is employed to firstly pre-cool the ambient air which is then implemented to cool the back surface of the PV panel to simultaneously improve the PV panel performance. It was possible to decrease the PV module temperature from an average 55 °C (without cooling) to 42 °C with the help of geothermal pre-cooled air flow over the back surface of a PV module at an optimum rate of 0.0288 m3/s. At this optimum flow rate, due to the decrease in PV module temperature, an average improvement in the PV module output power and electrical efficiency of about 18.90% and 22.98% respectively was achieved. According to economics assessment, the relative levelized cost of energy is improved by 12% due to proposed cooling system which is helped in avoiding emissions of about 13896 g CO2 per summer season.

Monitoring Data Study of the Performance of Renewable Energy Systems in a Near Zero Energy Building in Spain: A Case Study

The building sector is responsible for a substantial part of the energy consumption and corresponding CO2 emissions. The European Union has consequently developed various directives, among which the updated Energy Performance of Buildings Directive 2018/844/EU stands out, aiming at minimizing the energy demand in buildings, improving the energy efficiency of their facilities and integrating renewable energies. The objective of the present study was to develop an analysis on the energy performance, related CO2 emissions and operating costs of the renewable energy technologies implemented within a multipurpose near Zero Energy Building (nZEB). The target building is an existing nZEB called LUCIA, located in Valladolid (Spain). Monitoring data provides the required information on the actual needs for electricity, cooling and heating. It is equipped with solar energy photovoltaic systems, a biomass boiler and a geothermal Earth to Air Heat Exchanger (EAHX) intended for meeting the ventilation thermal loads. All systems studied show favourable performances, but depend significantly on the particular characteristics of the building, the control algorithm and the climate of the location. Hence, design of these strategies for new nZEBs must consider all these factors. The combined use of the PhotoVoltaic PV System, the biomass and the EAHX reduces the CO2 emissions up to 123 to 170 tons/year in comparison with other fuels, entailing economic savings from the system operation of up to 43,000–50,000 €/year.

Parametric study and optimization of a solar chimney passive ventilation system coupled with an earth-to-air heat exchanger

A parametric analysis and optimization method for passive heating and ventilation systems are developed, using the computational fluid dynamics (CFD) ANSYS design exploration and optimization tool. Moreover, a three-dimensional, quasi-steady CFD Fluent simulation is performed and validated against experimental results. For comparison, the thermal performance of a small-scale wooden room fitted with a solar chimney and an earth-to-air heat exchanger (EAHE) was experimentally evaluated in the cold season in Egypt, in March 14–22, 2016. A good agreement has been found between the experimental and simulated results, with error, correlation coefficient, and coefficient of determination average values of 7.3%, 96.5%, and 94%, respectively. Moreover, a parametric study is conducted to maximize the ventilation rate, using eight parameters for solar chimney configuration (width, length, air gap, inclination angle, and position) and EAHE design (pipe diameter, inlet position, and inlet height). It is found that the EAHE pipe diameter is the most sensitive parameter, followed by chimney height, and EAHE inlet height and position; the solar chimney inclination angle, width, and gap have also noticeable impacts. The optimum chimney inclination angle, length, width, and gap ranges are 30–35°, 1.94–1.97 m, 0.92–0.97 m, and 0.19–0.23 m, respectively.

Performance Analysis of Air Cooled Heat Pump Coupled with Horizontal Air Ground Heat Exchanger in the Mediterranean Climate

A concept of Air-Cooled Heat Pump (ACHP) coupled with a Horizontal Air-Ground Heat Exchanger (HAGHE), also called Horizontal Earth-To-Air Heat Exchanger (EAHX), has been proposed. The Air-Cooled Heat Pump is a system which transfers heat from outside source (air) to inside sink (water) and vice versa in summertime. The innovation is to provide a geothermal treatment of pre-heating/cooling of air before meeting the evaporator in winter or the condenser in summer of the heat pump. Besides, it is known that the variations of the ground temperature, respect to the external air one, are mitigated already in the first layers of the ground throughout the year, due to the high thermal inertia of the ground, letting the heat pump work with more mitigated conditions, improving the performances. The behaviour of HAGHE has been investigated by varying the length and the installation depth of the probes, the air flow rate and the ground thermal properties. All the combinations have been implemented using TRNSYS 17 software (Transient System Simulation Program) to obtain the outlet temperatures from HAGHE, resulting from the 54 configurations. The results are compared in terms of Coefficient of Performance (COP) in wintertime and Energy Efficiency Ratio (EER) in summertime between configurations with and without the coupling with HAGHE. In addition, two seasonal performance SCOP and SEER coefficients have been calculated considering, not only the inlet air temperatures into the Air-Cooled Heat Pump, but also their frequency of occurrence, the off-set external temperature (16 °C), the nominal external temperature and heating and cooling loads.

Design of a Ventilation System Coupled with a Horizontal Air-Ground Heat Exchanger (HAGHE) for a Residential Building in a Warm Climate

Energy consumption in new buildings can be reduced at the design stage. This study optimizes the ventilation system design of a new residential building located in a warm climate (Southern Italy). Different system options of horizontal air-ground heat exchangers (HAGHEs), also called earth-to-air heat exchangers (EAHX), have been considered to search for the optimal configuration. The thermal behaviour of the obtained configurations has been modelled by the dynamic simulation software TRNSYS 17. The pipe numbers, the air flow rate, and the soil thermal conductivity are among the simulated building components. For each of them, different design options have been analysed to study how each parameter impacts the building thermal behaviour in winter and summer. The operative air temperature (TOP) has been evaluated inside the building prototype to investigate the indoor comfort. The paper demonstrates that HAGHEs permit to assure a suitable indoor climatization if the building envelope is optimized for a warm area. These conditions require high values of heat storage capacity to keep under control the internal temperature fluctuations, especially in summer. The paper confirms the importance of geothermal systems and design optimization to increase energy savings.

EAHX – Earth-to-air heat exchanger: Simplified method and KPI for early building design phases

Earth-to-air heat exchangers (EAHX) are a recognised technology which are able to naturally pre-cool and pre-heat an airflow. In this paper a method is presented to analyse the potentiality of this technique in specific locations in order to optimise and check their ability to cover the expected building energy demand as early as possible. The proposed method is conceived for early-design phases and includes a model to estimate outlet air temperature after EAHX treatment including an average local meteorological year, soil typology and early-design choices. The model is further validated on long-term experimental data and used to develop 3 Key Performance Indicators (KPI) to better define the early design conception of an EAHX in the site context. These KPI include the analysis of activation hours based on a psychrometric chart, the calculation of the expected sensible heat exchange of the system (winter and summer), and the “virtual” COP in consideration of the theoretical calculation of pressure drops. Finally, main limitations of this simplified approach are discussed.

Thermal design of Earth-to-air heat exchanger. Part II a new transient semi-analytical model and experimental validation for estimating air temperature

Abstract This paper is the second in a series of thermal design of Earth-to-Air Heat Exchanger (EAHE). The first part explains a transient semi-analytical model ‘named RBM model’ to estimate the disturbed soil thermal resistance of EAHE pipe as a function of duration of operation. In this part, a new semi-analytical model, called Generalized RBM model (GRBM model), is developed to predict the thermal performance of EAHE operating under transient conditions for cooling mode. Therefore, an experimental investigation was carried out in the region of Biskra (Algeria) to validate the developed model. The GRBM model development is based on the subdivision of the soil and the pipe into many layers and the use of RBM model, presented in the first part, to estimate the temperature of disturbed soil surrounding the inspected layer. Furthermore, the experimental horizontal EAHE setup, installed in the University of Biskra, is described. The experimental tests were performed in May 2013 for 6 h of continuous operation mode of the EAHE setup. To validate the GRBM model, a comparison between the calculation and the experimental results at various sections along the pipe is conducted. The results of the GRBM model are in a good agreement with the measured temperatures with an average relative error of 2.8%. Furthermore, both analytical aspect and the simplicity of the GRBM model will make the thermal design of EAHE more accurate with significantly reduced calculation time.

Heat and Mass Transfer Behavior Prediction and Thermal Performance Analysis of Earth-to-Air Heat Exchanger by Finite Volume Method

A comprehensive numerical study on coupled heat and mass transfer in an earth-to-air heat exchanger (EAHE) is conducted by self-complied program based on the finite volume method. The soil thermal and moisture coupled characteristics in the vicinity of the pipe and the thermal performance of the EAHE are evaluated by a two-dimensional simulation model. The model of the EAHE is verified by the experimental data, which achieved a good agreement with each other. The numerical results show that there is an obvious moisture peak in the radial direction, and the peak position radially moves away from the wall of the pipe over time. It is also found that the thermal performance of the heat and mass transfer model in soil is better than the pure heat conduction model.

EVALUATING THE INFLUENCE OF SOME DESIGN AND ENVIRONMENTAL PARAMETERS ON THE PERFORMANCE OF EARTH TO AIR HEAT EXCHANGER


 The earth to air heat exchangers (EAHE) is effective passive cooling and heating techniques for buildings. This paper studies numerically the effect of some design and environmental parameters (moist content of soil, pipe material and thickness of pipe wall) on the overall performance of EAHE system. Three types of soil were selected (dry soil, moist soil and saturated soil) with two pipe materials PVC and steel and three thicknesses of pipe wall (2, 3 and 6 mm). This numerical study has been done for summer and winter seasons according to the weather conditions for Nasiriyah city in southern of Iraq. First the built numerical model was validated against experimental model and the results of comparison showed good agreement. After the validation the overall performance of EAHE system with selected parameters was analyzed with ranges of air velocity, inlet temperature and pipe length of 50 m. The simulated results showed that the very moist or saturated soil gives the best overall performance of EAHE system compare with other soils, Furthermore there is no significant effect of pipe material and wall thickness on the overall performance.
 

Coupling of earth-to-air heat exchangers and buoyancy for energy-efficient ventilation of buildings considering dynamic thermal behavior and cooling/heating capacity

Energy-efficient technologies such as earth-to-air heat exchangers (EAHEs) and buoyancy-driven natural ventilation (BV) are employed for space conditioning. However, a fan is required in conventional EAHEs for air circulation, and BV normally serves as a passive cooling measure in temperate transitional seasons. This paper proposes the coupling of EAHEs and the buoyancy generated inside a building to achieve passive and autonomous ventilation without requiring any mechanical system. A model is developed to investigate the effects of the coupled system, with a primary focus on the dynamics of the airflow temperature, flow rate, and cooling/heating capacity provision. The model results are in good agreement with those of the computational fluid dynamics simulation. The model is applied in a hypothetical building located in a hot-summer/cold-winter region (Chongqing, China). The proposed coupled scheme is superior to the BV in hot and cold seasons. The indoor air temperature, ventilation flow rate, and cooling/heating capacity are found to fluctuate asynchronously. The cooling capacity is 56.3 kWh for the hottest day, and the heating capacity is 111.1 kWh for the coldest day. The maximum cooling or heating capacity is nearly achieved at the hottest or coldest times with the help of ventilation flow rate fluctuation.

Cooling performance of earth-to-air heat exchangers applied to a poultry barn in semi-desert areas of South Iraq

Earth-to-air heat exchangers (EAHE) can reduce the energy consumption required for heating and cooling of buildings. The composition and the thermal characteristics of the soil influence the heat exchange capacity, and the soil moisture can furthermore affect thermal performance of EAHE. The aim of this study was to compare the thermal performance of EAHE in dry and artificially wetted soil. Tests were carried out in the Basra Province (Iraq), in a semi-desert area. Two experimental EAHE were built in a poultry barn and tested from June 2013 to September 2013. The pipe exchangers were buried at 2 m deep. One heat exchanger operated in dry soil (DE), while the other one operated in artificially wetted soil (WE). In the WE system, a drip tubing placed 10 cm above the air pipe wetted the soil around the exchanger. Air temperatures at the inlet and at the outlet of both the exchangers as well as soil temperature at 2 m deep were continuously monitored. The experimental results confirmed that wetting the soil around EAHE improves the general heat exchange efficiency. The coefficient of cooling performance (COP) of the earth-to-air heat exchangers system was evaluated on the basis of the ratio between the heat removed from the air or added to the air and the energy input. During the day, with an average COP of 6.41, the WE system cooled the air more than the DE system, which reported a value of 5.07. On average, in the hottest hours of the day, the outlet temperature of the WE was 37.35°C while in the DE it was 38.91°C. Moreover, during the nighttime, the WE system warmed the air more than the DE system. Keywords: Earth-to-air heat exchangers, thermal performance, cooling, artificially wetted soil, poultry barn, heat stress DOI: 10.25165/j.ijabe.20181103.3047 Citation: Morshed W, Leso L, Conti L, Rossi G, Simonini S, Barbari M. Cooling performance of earth-to-air heat exchangers applied to a poultry barn in semi-desert areas of south Iraq. Int J Agric & Biol Eng, 2018; 11(3): 47–53.

Validation of CFD model for simulation of multi-pipe earth-to-air heat exchangers (EAHEs) flow performance

In this paper the experimentally obtained flow characteristics of multi-pipe earth-to-air heat exchangers (EAHEs) were used to validate the EAHE flow performance numerical model prepared by means of CFD software Ansys Fluent. The cut-cell meshing and the k-ε realizable turbulence model with default coefficients values and enhanced wall treatment were used. The total pressure losses and airflow in each pipe of multi-pipe exchangers was investigated both experimentally and numerically. The results show that airflow in each pipe of the multi-pipe EAHE structures is not equal. The validated numerical model can be used for a proper designing of multi-pipe EAHEs from the point of view of the flow characteristics. The influence of EAHEs geometrical parameters on the total pressure losses and airflow division between the exchanger pipes can also be analyzed. Usage of CFD for a designing process of EAHEs can be helpful for HVAC engineers (Heating Ventilation and Air Conditioning). It can also be helpful for optimizing the geometrical structure of multi-pipe EAHEs in order to save the energy and decrease operational costs of low-energy buildings.

Climate-potential of earth-to-air heat exchangers

Amid several natural cooling sources that refer to thermal sinks (water, air, ground and night sky), a possible system is represented by the horizontal earth-to-air heat exchangers (EAHX). This technology, even if less diffused if compared to other geothermal systems, has been demonstrated to be effective alone and coupled with mechanical air-handling systems to reduce the energy consumption for both cooling and heating.After a short review of existing EAHX simulation software, the paper will introduce a new simplified method to assess the potential of earth-to-air heat exchangers according to local soil composition and climate data.

Numerical analysis of the efficiency of earth to air heat exchange systems in cold and hot-arid climates

In order to examine and compare the efficiency of earth to air heat exchanger (EAHE) systems in hot-arid (Yazd) and cold (Hamadan) climates in Iran a steady state model was developed to evaluate the impact of various parameters including inlet air temperatures, pipe lengths and ground temperatures on the cooling and heating potential of EAHEs in both climates. The results demonstrated the ability of the system to not only improve the average temperature and decrease the temperature fluctuation of the outlet air temperature of EAHE, but also to trigger considerable energy saving. It was found that in both climates, the system is highly utilized for pre-heating, and its usage is unfeasible in certain periods throughout the year. In winter, EAHEs have the potential of increasing the air temperature in the range of 0.2–11.2°C and 0.1–17.2°C for Yazd and Hamadan, respectively. However, in summer, the system decreases the air temperature for the aforementioned cities in the range of 1.3–11.4°C and 5.7–11.1°C, respectively. The system ascertains to be more efficient in the hot-arid climate of Yazd, where it can be used on 294days of the year, leading to 50.1–63.6% energy saving, when compared to the cold climate of Hamadan, where it can be used on 225days of the year resulting in a reduction of energy consumption by 24.5–47.9%.