Low exergy modelling and performance analysis of greenhouses coupled to closed earth-to-air heat exchangers (EAHEs)

The present study deals with modelling, analyzing and assessing the performance of greenhouse heating systems with earth–pipe–air heat exchangers (EAHEs) in closed loop mode. In this regard, an EAHE system is considered as an illustrative example. This system starts with the power plant, through the production of heat (EAHE), via a distribution system, to the heating system and from there, via the greenhouse air, across the greenhouse envelope to the outside environment. Exergy analysis method (the so-called low exergy or LowEx approach) has been and still being successfully used to design and evaluate sustainable buildings. It is applied to all components of this EAHE system for the first time to the best of the author's knowledge in this study. The overall energy efficiency value for the EAHE system studied is determined to be 72.10% while the overall exergy efficiency value is calculated to be 19.18% at a reference state temperature of 0 °C. The exergy efficiency of the whole EAHE system decreases from 19.18% to 0.77% with the increase in the reference environment temperature from 0 to 18 °C. The sustainability index values for the whole EAHE system decrease from 1.24 to 1.01 as the reference state temperature increases.