Analytical modelling of Breathing Walls: experimental verification by means of the Dual Air Vented Thermal Box lab facility

Abstract

Breathing Walls are air permeable envelope components based on porous materials. In contra-flux operation air flows opposite to \ud conductive flux, while in pro-flux they have the same direction. The Breathing Wall behaves either as a ventilation heat exchanger \ud or as an active insulation. \ud In literature an analytical model describing steady state heat transfer across a Breathing Wall can be found. Since it lacks an \ud exhaustive experimental validation, a facility developed at the Energy Department of Politecnico of Milano was used to investigate \ud the thermo-physical behavior of a no-fines concrete based Breathing Wall in steady state Dirichlet conditions and contra-flux \ud operation

Experimental validation of a steady periodic analytical model for Breathing Walls

“…Overall, it was demonstrated how this technical solution is able to recover part of the conductive heat losses by pre-heating the fresh air coming from outside, so that the Breathing Wall can be seen as a recovery heat exchanger whose efficiency depends on the air flow velocity [11]. Moreover, in winter contra-flux steady state condition it was demonstrated both analytically [8] and experimentally [12,13] that the heat exchange at pore scale leads to an exponential trend of the temperature distribution and to the cooling of the inner surface [14,15]. Since the air crosses inward the solid matrix at very low speed, the permeable layer acts also as high efficiency filter for PM2-10 [16].…”

“…The steady-state solution was already presented in past works [8,26] and experimentally validated in [12,13]. Starting from Eq.…”

“…Since the steady-state behaviour of Breathing Walls has already been thoroughly discussed in the past [8,12,13], no further investigation will be presented in this paper.…”

“…where it is possible to observe that the time variable has been eliminated, since it only appears in the e iωt factor in Eq. 12, (13) and (14). The solution of this problem is:…”

“…The experimental validation of the steady periodic analytical model reported in this paper is performed on a BW sample tested in the Dual Air Vented Thermal Box. The laboratory rig, firstly presented in [12,13], has been specially improved in order to reproduce dynamic boundary conditions. The performance of the apparatus and the results of the comparison between the measurements and the model calculations are presented and discussed in the paper.…”