Earth-Air Heat Exchangers (EAHE): Exergetic Analysis

To facilitate the energy transition, it is necessary to develop sustainable energy technologies. The Earth Air Heat Exchanger (EAHE) is such technology, which can reduce energy consumption by a building significantly. The Earth-Air Heat Exchanger (EAHE) is an air-soil exchanger buried under the ground that permits the use of shallow ground temperatures to decrease building’s heating and cooling demands. As any energy system, EAHE is subject to the first and second law of thermodynamics. The first law well describes the performance of the system from an energetic point of view however the real behavior of the system is also related to entropy that determines energy availability (or exergy) in the system. The exergy analysis which results from combing both the first and second law of thermodynamics helps to analyze the performance of the system at its reversible limit and to estimate the departure from this limit. This leads to determining the exergetic efficiency of the system which assesses the system in reference to its best situation (reversible case). In this paper, an exergetic analysis will be carried out on the EAHE installed at ICUBE, Illkirch-Graffenstaden campus of University of Strasbourg. The EAHE is composed of a polyethylene pipe buried under the ground up to a depth of 1.2 m with a total length of 29 m. The horizontal part of the EAHE is composed of three different sections where each section is coated by a different type of coating soils; (1) sand, (2) sand-bent: a mix between sand and bentonite (3%), and (3) initial natural earth soil. The system is equipped with thermal sensors to measures the soil and air temperature with an uncertainty of 0.1∘^{\circ}C. The objective is to assess the system and identify the parts that dissipates energy the most to optimize the system. The experimental EAHE and the measurements taken are presented in this paper as well as the equations used in the analysis and finally the derived results are analyzed.