This post will try to convey a sense of how natural ventilation can be enhanced by Cube-based Shelter’s characteristic geometry. As such, breathability is an extension of the style’s passive solar design attributes with the goal being to minimize the need for fans and air conditioners.
So far the only references made to address natural cooling entailed shutting out high sunlight from equator-facing wall glazing with a flat roof extension and specifying a high albedo solar roof base such that the area remaining after PV panel placement is sufficient to produce a net cooling effect.
At the lower end of the solar roof, the horizontal extension should situate high enough to allow air currents (from the general direction of the equator) passage through vents over glass doors and windows. If not, slatted vents might be incorporated between glass elements on that wall. The porch area defined by the flat roof can be employed to effect additional cooling by supporting a shallow water reservoir that cools as it evaporates.
Or, the reservoir might supply water for a wicking material like burlap stretched vertically to the ground, with the resultant cool air produced from evaporation caught in the path of air movement into the house. Alternatively, the outside vertical plane defined by the roof extension can be a air permeable green walls of climbing flora, that create shade, and cools air by evapotranspiration.
Once inside, air may exit through vents on east and west walls. Of upmost importance is that the warmest and uppermost air have a means to escape which is afforded by quarter circle roof ridge vents.
As with portholes indigenous to those planes vents are fully circular, or can share circular areas with glass partitioned according to CBS Geometry.Vent slats might also be rotated vertically to admit change of season air from the general direction of the poles.
In the absence of external air movement to tap into, the CBS cross-section poses a geometry having implications worth considering. As a general principle, asymmetry begets movement. How that principle plays out physically with disparately angled ceiling slopes would most likely be initiated by air rising from the floor or a heat source like people. Like the sun’s radiation falling on the uneven terrain of mountain ranges to induce microclimate breezes, the resulting temperature and pressure differences arising from the varying planes of the interior terrain should induce air movement.
Conversely, the symmetry posed by the cross-sections of a flat or symmetrically sloped ceiling would more likely cause air movement to reach an equilibrium, and stagnate. Not that the CBS cross-section would induce a howling vortex, but the notion that subtle currents would naturally move in a pattern following the asymmetry’s intrinsic circular basis certainly seems reasonable. That movement would likely be biased in a counter clockwise direction in winter from low sun striking the most exposed floor area near the most glazing, and clockwise in summer from striking the polar side of the house. As air encounters the hard (90*) angle at the ceiling’s apex, stopped momentum would tend to encourage air toward east and west wall vents.
This dynamic can be enhanced by tapping into solar chimney effects that create and releases heat from the sun upward during the warmer months to draw up cool air from below into a circulation pattern.
To control and guide these air movements to need, the open beam ceiling joists of the CBS grand room structure can be used to support light movable horizontally-oriented panels.
Or the joists can serve to hang drapes and or sliding vertically extended panels.
Heat flow considerations require that adequate insulation be provided for all the home’s glazing, perhaps sliding Styrofoam-cored panels for doors, and upholstered cylindrical foam pads for portholes. With regard to the roof, recent building code specifications apparently do not distinguish between R-Values required for flat ceiling and a sloped roof even as the latter is in fact part wall to the extent of its steepness. To avoid installing unnecessary insulation (along with the extra material to accommodate it), a way to calculate the R-value for a particular slope in a particular climate zone is given by the above. For example if you are at 40* latitude and your climate requires R38 for the ceiling and R20 for the walls, the R value for your equator-facing roof is R34. The formula – being reverse engineered as it is – may be oversimplified; but if it errs, I believe it does so on the side of caution, yielding more insulation than necessary. Even so, if you intend to size your roof thickness and insulation with this equation, check with your building inspector first.
Such are the low entropy ways in which CBS geometry addresses comfort. Additional approaches will come with cool tubes buried in earth embankments which will be described later with posts regarding Ground Design. For now, the embanking specifications can be viewed in this PDF.