Effect of boundary conditions on the performance of earth-to-air heat exchange systems in Valladolid (Spain)

Abstract

The increasing concern on energy demand in the building sector and the international commitments to combat climate change have lead to the spread of near Zero Energy Buildings (nZEB). Earth-to-Air Heat Exchangers have been recognized as one cost-effective potential to contribute to Zero Energy Buildings requirements, and the related research has demonstrated their remarkable technological attractiveness at different scales [2], leading to an extensive amount of recent literature on the topic. Earth-to-Air Heat Exchangers (EAHE) consist of a set of ducts buried in the shallow ground (2.5-3 m depth), with their inlets connected to the outdoor air and their outlets terminating directly in the building space or feeding pre-treated air to the building’s air handling unit (AHU). Hence, they supply pre-heated or pre-cooled air to the building, depending on the season, thanks to the ground’s properties that makes its temperature lag behind atmospheric air temperature, making it possible for the ground to act both as a heat sink and a heat source, depending on the season. There are numerous designs of EAHE, but these can be grouped into open loop, if they provide outdoor ventilation air, closed loop, if they operate in recirculation mode, and hybrid, if coupled with other systems. An EAHE can be composed of only one tube or a number of parallel tubes, which can be arranged to classify as horizontalstraight, vertical looped, slinky or spiral, and pond or helical looped arrangements. However, the factors that determine the performance of the EAHE are numerous, including not only the particular climate and operating conditions, but also the soil properties and the characteristics of the pipes [4], which complicates the appropriate analysis of the system’s performance. Published empirical research does not focus on tertiary buildings intended for higher education activities and are limited to a range of climates. In this work, the performance of two EAHEs placed in the same city is compared, to evaluate the effect on the performance of the different boundaries of the ground where the system is installed.