Search

The primary goal of this paper is to assess the thermal behaviour of Earth-to- Air Heat Exchanger (EAHE) under continuous operation mode during the cooling period in warm climatic conditions. An experimental setup was conducted in Biskra University (Algeria) to test the ability to use EAHE as an alternative solution to conventional air conditioning systems. Besides, a transient numerical approach for the flowing air within the EAHE was developed using energy balance equations, discretised by the implicit finite differences method and solved by Thomas method. Furthermore, the transient temperature profile of the soil around the EAHE was investigated in order to determine the adiabatic radius of the soil as a function of the duration of operation. In this context, a transient semi-analytical model was integrated to the air model to estimate the transient EAHE's performance deterioration. This deterioration is produced by the thermal saturation of the soil, which is influenced by the heat released from the air inside the pipe. Results showed that continuous operation for a duration of four days has minimal impact on the outlet air temperatures due to the implementation of night purging. Furthermore, the design and thermal efficiency of the EAHE are impacted by factors such as higher air velocity and reduced soil thermal conductivity. [ABSTRACT FROM AUTHOR]

The current study focused on the adaptation of adsorption cooling systems to hot and arid climates. A new combination is proposed to improve the performance of the direct evaporative cooler (DEC). This combined system consists in coupling Ground-Water Heat Exchanger (GWHE) with a DEC of a hybrid cooling tower. A mathematical model has been developed and validated to depict the heat and mass transfer that occurs in the DEC between the air and water, as well as between the ground and water in the geothermal heat exchanger. The key variables taken into consideration are the outdoor air temperature and the mass flow rate and the temperature of water. The effect of the inlet hot air velocity and temperature, and water mass flow rate, on the evaporated water is investigated. The findings indicate that the mathematical model of a DEC coupled to GWHE predicts optimal characteristics, leading to a reduction in the air temperature from 48°C to 32°C at the heat exchanger inlet of the cooling tower. [ABSTRACT FROM AUTHOR]

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

This article is the first in a series about the thermal design of Earth-to-Air Heat Exchanger, EAHE, using a new developed semi-analytical method. The temperature distribution in the soil surrounding the EAHE is studied in the goal to determine the soil radius as a function of the operation duration. This radius is the first distance from the pipe axis where there is no effect of heat from EAHE. For that, a new transient semi-analytical model is developed in particular to facilitate the thermal design of EAHEs. The main application of the developed model is to predict the deterioration in EAHE's thermal performance as a function of the duration operation. This deterioration can be caused by soil thermal saturation where the nearby subsoil temperature becomes almost equal to the inlet air temperature resulting in minimum heat transfer between air and soil. The analytical solution of the proposed model has been integrated by means of the Bessel function method, for a constant heat flux per unit of length at the pipe surface in the radial dimension and constant inlet air temperature. The model has been verified with several results obtained from the literature. In addition, an investigation of continuous operation of an EAHE is made on thermal performance of the EAHE in the soil of the region of Biskra (Southern Algeria) (34°47′N - 005°43′E) by applying extreme ambient air temperature (57 °C). Results show that the deterioration in thermal performance of EAHE is observed for longer duration in hot and dry climate. In the case of 6 h of continuous operation, the soil radius can reach 0.55 m from the pipe surface. The model proposed in this paper can be considered as the first of its kind which gives a formula for calculating the soil radius (thickness) as a function of the: i) duration of operation, ii) soil thermal diffusivity, iii) pipe diameter and iv) air temperature. [ABSTRACT FROM AUTHOR]

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. Highlights • New transient semi-analytical model is proposed to design EAHE. • Geothermal experimental data of the Biskra region (Algeria) were presented. • Semi-analytical results were validated with experimental measurements. • Generalized RBM (GRBM) model presents a significantly reduced calculation time. • GRBM model can be used to predict the deterioration of EAHE thermal performance. [ABSTRACT FROM AUTHOR]

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 CO 2 emissions during its lifespan, in contrast, its simple payback time estimated 4 years. • The contribution of an earth air heat exchanger in improving the indoor conditions of a poultry house. • Simulate the potential design, position, and installation configuration scenarios. • Installing the earth air heat exchanger improved the indoor temperature and velocity. • The third scenario is the optimal design for indoor air uniformity. • The simple payback period of the earth air heat exchanger is four years. [ABSTRACT FROM AUTHOR]

The main objective of the present study is to investigate the thermal performances of an earth air heat exchanger (EAHE) under transient conditions in cooling mode. This work was performed experimentally in the University of Biskra, Algeria. For that, a PVC pipe of 53.16 m long and 110 mm diameter buried at 3 m depth is used. Tests of the experimental setup were carried out in continuous operation mode for 71 hours with high inlet temperatures. Besides, a mathematical model was presented for EAHE by using the finite differences method applying the energy balance equations with forced convection. In addition of the horizontal portion on soil surface, the two vertical portions of 3m each one connected to the horizontal portion were considered in the modeling in order to present a fairly complete study of the EAHE. It was found that the continuous operation mode have no remarkable effect on the outlet air temperature and thus on the EAHE performances during all 71 hours. Results of the theoretical predictions were validated with the measured air temperatures along the EAHE and showed satisfactory qualitative and quantitative agreement. [ABSTRACT FROM AUTHOR]