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.