Z E M C H 2 0 1 2 I n t e r n a t i o n a l C o n f e r e n c e
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This paper shows the potential of leeward sawtooth roof for increasing ventilation rates
by the optimization of its geometry. An aerodynamic approach is necessary for its
optimization. The sawtooth roof geometries could be an industrialized architecture
component and make it more affordable.
The on-floor air diffuser position is important for the internal air stream flow distribution.
Since the plenum is pressurized, the on-floor diffuser localisation criterion is a function of
the occupancy zones and heat source areas. There is no restriction for its location at the
floor plan, giving flexibility to the layout organization design process. Ventilation flexibility
is important as the wind speed is not always enough for achieving thermal comfort
ranges. Some examples of ventilation flexibility are obtained by the upward wall (cross
ventilation) and also by the floor level (on-floor diffuser) as shown in figure 11. Flexible
ventilation systems can help to provide alternatives to problems such as noisy
environment.
5.2. Air velocity distribution and ventilation rate
An efficient air draft or tube stream flow crossing the building could be good enough to
provide thermal comfort to occupants. Both air velocity distribution and ventilation rate
are parameters to measure the natural ventilation efficiency. The interaction between
both should be assessed. We believed that low ventilation rates with an efficient draft
provide thermal comfort to the occupant. The ventilation rate levels are important to
guarantee air quality and thermal comfort inside the building. In hot and humid weather,
ventilation rates are defined by the high levels required to achieve thermal comfort.
6.
Conclusions
The paper showed an application of the on-going authors´ research in which the relevance of
the sawtooth roof geometry in natural ventilation is analysed. The roof geometry has great
importance to increasing the pressure coefficient module at the leeward opening. From the
three sawtooth roof geometries cases, model D1 presents a slightly better performance.
However, other sawtooth roof geometries will be evaluated.
The negative pressure coefficient, induced by sawtooth roof geometries, such as model D1
can create higher ventilation rates. Keeping a negative outlet-opening surface pressure is
fundamental for the upward-airflow natural ventilation systems. When the negative pressure
coefficient is larger the ventilation ratio also can be increased. Getting a high negative
pressure coefficient at the outlet opening by using the geometry is a parameter of primary
importance for sucking the air out of the house even during low wind speed.
By using the on-floor air diffuser by naturally pressurized plenum the ventilation rates
can be increased.
The naturally pressurized plenum shows that even at low wind speed
(1m/s) it can discharge air, by the on-floor air diffuser, within considerable air speed range,
1m/s and 2m/s and complement the internal air distribution. In summary, the results pointed
its potential for working together with natural cross ventilation and for generating an air
stream at the deepest areas of the room which is important to avoid stagnation zones.
The simplified geometry of the typical tropical house and the application of the upward-
airflow ventilation system show a possible solution for being incorporated into this house
architecture. Furthermore, the naturally pressurized plenum could be a floor-box
prefabricated component.
The effect of the leeward sawtooth roof geometry in ventilation was shown. More roof
geometry studies and scenarios should be carried out in order to better understand these
phenomena. Architectural applications such as occupancy zones or layout organization are
also interesting to be considered.
