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
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3. Upward-airflow ventilation system and architecture concept
It is known that during low wind speed, the ventilation rates are dominated by the stack
effect (Liddament 1996). Although the thermal buoyancy (stack effect) was not
considered in our simulation, the performance of the upward-airflow ventilation system
during low wind speed shows its considerable potential. Even with a low wind speed of
1m/s there is an upward air stream flow of similar velocity at the middle of the on-floor
diffuser located (Fig. 16). This upward air stream flow is a consequence of the natural
pressurization of the plenum, which is large enough and its inlet-outlet opening ratio
(31:1) is appropriate to induce it by the wind; this stream flow is important for
complementing the ventilation rate and avoids the stagnation zones at the bottom of the
room.
Figure 10. Architectural Induced Pressure
gradient - conceptual scheme.
Figure 11. Ventilation System: Stream tube flow (I1 –
S); (I2 – S); (Edn – S) (Perén et al. 2011).
3.1. Combining temperature difference and wind driving forces [
∆P f(T e U
)]:
As we have a higher temperature difference between a house and its environment, the
upward ventilation system efficiency is increased. In hot and humid weather, there is a
limit to take advantage of temperature difference if compared with the higher
temperature difference (more than 6°C) that can be reached in other types of weather
such as hot and dry. Even though sawtooth roof have this potential, another way to
observe the effect of the sawtooth roof geometry and on-floor air diffuser is considering
critical conditions such as low window opening area (10%) and low wind speed (1m/s).
Furthermore, the ceiling height is another important parameter to be considered for
increasing ventilation performance. The three sawtooth roof models studied in this paper
have a maximum 6-meter ceiling height.
3.2. Increasing the ceiling height (∆h) and conducting the air flow
In hot and humid weather, higher ceiling levels are crucial to lift the stratification zone as
high as possible. The up-ward air flow ventilation can also push up the air by injecting
the air at the floor level. This on-floor air injection can be led and supplemented by
mechanical ventilation, as necessary in hybrid ventilation system cases, as João
Filgueiras proposed for the Fortaleza and Salvador Sarah Hospitals. Elevated and two-
storey houses where there is a shaded place at the ground level such as a garage or
another common area can take advantage of this upward ventilation system since the air
in this zone is hypothetically cooler than at adjacent and upper levels. When possible,
convective ventilation can move the air as there is a ∆T and ∆h. Further research can
analyse this passive strategy to draw fresh air inside the building from the lower levels of
the house.
