Design of nearly zero energy buildings coupled with an earth to air heat exchanger in Mediterranean climate: Development of an analytic model and validation against a monitored case study

At the Passivhaus of Cherasco, located in Pianura Padana (Italy), an earth to air heat exchanger (EAHE) and natural night ventilation (in summer) are used to deliver comfort conditions with very low energy consumption. One  year and a half of continuous measurements have been carried out in order to evaluate the energy and comfort performances of this building, which combines the Passivhaus concept with local architectural solutions. We present an analysis of the system constituted by building envelope and EAHE. Monitored data  (with a particular focus on cooling potential) were evaluated with the use of established indicators and compared with simulations performed by coupling dynamic simulation software (EnergyPlus) and an analytic model for the EAHE. Based on this analysis a simplified steady-periodic model is developed  to provide an estimate of the behaviour of the coupled system  building envelope (including night ventilation) and EAHE from the point of view of energy and comfort, over a period of few weeks. The model is validated towards monitored data and shows a good agreement in terms of temperature profile, with a slight phase discrepancy, as expected based on the simplifying assumptions about thermal capacity effects. The analytic model is proposed as a tool for (i) evaluating the integration of EAHEs during the early design phase and (ii) optimise their operation under variable weather and occupation conditions, via incorporation in the control software of the building.