Breathing walls, does it make sense?

logo_smallBreathing walls are requested due to the “sick building syndrome“. This illness is attributed (without real proof) to air conditioning, out-gassing of some materials (VOC), too small intake of fresh air, mold and ozone. We may assume that depending on the person some of these products are indeed not positive for the health. Generally, there are two solutions:

  • The passive housing system with air tight walls and forced ventilation
  • The breathing wall system

passive-house-illustrated-simplicityThe passive housing system is the well known. Air tight walls with a very large thermal resistance (U=0.1 W/m2K) where all the fresh air comes from forced ventilation. The intake air is heated by the air leaving the building with a heat exchanger between both flows. Due to the low heat flow, the wall may be a source of interstitial condensation, generating mold while also the heat exchanger needs regular cleaning to avoid mold. On top of that, the limited diameter of the ventilation channels is the reason of high air speed regions in the house, which is not comfortable. It is clear that passive housing is not the favorite for people suffering from the sick building syndrome.

1-s2.0-S2212609013000046-gr1On the other hand, the breathing wall system is solving all the above problems. In a previous post, we used another definition: Dynamic insulation. In this case, cold outside air is sucked through the wall and heated with (low value) heat, which tries to leave the building. This sucking happens with a fan and the heat is stripped of the (warm) air by a heat exchanger and returned into the building. In this way, we have a low energy building with a very low air velocity ventilation and no possibilities for interstitial condensation in the wall, while the cleaning of the heat exchanger remains. A serious disadvantage is that wind on the building creates pressure differences in the building and also outside odor comes into the building.

An Hungarian paper lists the advantages of breathing walls (or dynamic insulation) while a more technical paper treats the dynamic insulation as a heat exchanger. Theory and experiments are given to know the real efficiency of dynamic insulation.

7f6d2b30dc77e32e369d51a258707ec3-Alma_22It is clear that open cell cellular glass can play a role in this dynamic insulation but I do not believe in breathing (dynamic insulation) walls due to wind problems. However, a breathing ceiling would be a nice application. Fresh air is pumped through a ceiling, constructed with open cell cellular glass, generating a ventilation over a large surface with extremely low air velocity. Besides ventilation, the open cell cellular glass serves also as acoustic absorber. I can imagine that this a perfect system for a student restaurant at the university. Ventilation and acoustic absorption, besides food are there the main issues.

 

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