Measuring Breathing Walls effectiveness and dynamic behaviour

A Breathing Wall is a building structure based on porous materials (e.g. pervious concrete, mineral wool or cellulose) crossed by an airflow, acting both as building envelope and ventilation system component. When operating in contra-flux configuration (heat flowing outwards and air flowing inwards) it behaves as a heat recovery system, while in pro-flux (heat and air mass both flowing outwards) it enhances building passive cooling. Therefore, in climates where both heating and cooling needs are relevant, both configurations might be alternated during the year or even the day. Understanding and modelling the Breathing Walls stationary and dynamic behaviour is thus fundamental, in order to optimize their design and fully exploit their energy saving potential. To this purpose, in this experimental study a small scale no fines concrete Breathing Wall is investigated. The steady-state contra-flux tests are used to derive the heat recovery efficiency of the sample as a function of the crossing airflow velocity. Effectiveness of this technology is then evaluated on a virtual case study. Dynamic tests, performed assuming a sinusoidal variation of the operative temperature on one side of the sample, show how airflow velocity affects the Breathing Wall inertia and dynamic behaviour.