U p w a r d – A i r f l o w V e n t i l a t i o n S y s t e m
765
1.3. Layout organization
The opening localization is linked to the program organization layout. For that, the
program organization is fundamental to guarantee cross ventilation efficiency. The
program organization plan should be spread (extended) instead of compressed in a
large square plan because natural cross ventilation has a practical limit in the inlet-outlet
opening distance that must be considered. This inlet-outlet distance should be no more
than 6 to 10 meters (Liddament 1996). Furthermore, the internal space organization
should follow the “open plan” criterion, which means avoiding internal walls, in order to
minimize the charge losses.
In contrast, the typical tropical house presented in this paper has a 14.5 x 14.5 square
meters plan and also has internal walls (see fig. 2 e 4). As a consequence of the large
square organization plan, some problems could be expected, such as badly-ventilated
zones and stagnation areas. To exemplify this situation, in our simplified model
simulation the air velocity at point S2 is less than 0.10m/s which is low if we consider that
it is a naturally ventilated house and the temperature in the tropical weather can reach
31°C or more (Fig. 17). However, the upward ventilation system presented in this paper
can be a complement to cross ventilation in order to solve this kind of problem (see fig.
19). More studies should be carried out in order to better evaluate the thermal comfort
levels.
The upward ventilation system should consider the program organization criteria as a
function of the weather, in which the sun and wind play a key role to chose the best
space distribution and house orientation. However, in terms of orientation for natural
ventilation purposes, the main variable must be the wind as our focus is to take
advantage of wind forces in the architecture component design. As a consequence of
this wind capturing dependence for refreshing internal spaces, the program organization
should be along the longitudinal axis of the predominant wind direction (Fig. 7).
Moreover, the program organization should avoid wind charge losses due to internal
walls, long distance between inlet-outlet openings and the external geometry envelope.
The organization axis proposed for this coupled cross and upward natural ventilation
approach is illustrated at figure
7 and 10.
2. Methodology
We here analyse the potential of the upward air-flow ventilation system and evaluate the
effect of three leeward sawtooth roof geometries in ventilation. This study was carried
out by using the Software Ansys CFX 13, based in Computational Fluid Dynamic - CFD.
For the ventilation simulation, the flow domain was established as an isothermal flow and
steady state analysis. The ventilation efficiency was tested for one wind incidence angle
(0°), normal to the main facade and four wind velocities (1m/s, 3m/s, 5m/s e 10m/s).
The study involves: three leeward sawtooth roof building models (Models A1, Model C1
and Model D1, showed at figure 8); two opening cases (Case A - cross ventilation and
Case B - with inlet diffuser at the floor level using a naturally pressurized plenum). A
combination of case A and B is also analysed. Section 4 presents more details of the
grid, computational domain and other simulation parameters.
2.1. Architecture components analysed
The potential for increasing natural ventilation of two architectural components was
analysed, the leeward sawtooth roof geometry and the on-floor air diffuser by naturally
pressurized plenum. The former works as an extractor fan (suction) and the latter works
as an inlet air diffuser (insufflation). Both the leeward sawtooth roof and the naturally
pressurized plenum - where the on-floor diffuser is located - have prefabrication potential
