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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3.3. Architectural features and pressure coefficient
The main architectural features of the leeward sawtooth roof models are listed in table 1.
Table 1: Main Architectural features of the Leeward sawtooth roof models
General
Parameters
(Case A and B)
Floor plan area
36m²
Internal floor plan area
33.75m²
Width
6m
Depth
6m
Internal volume average
109.60m²
Model A1
111.3m³
Model C1
112.4m³
Model D1
105 m³
Minimum ceiling height
3m
Maximum ceiling height
6m
Upwind facade area
18m²
Case A
(wall openings)
Wall porosity (Opening area/upwind facade area)
10%
Opening area
1.80m²
opening volume
0.18m³
Inlet-outlet opening ratio
1:1
Opening volume/Internal volume average ratio
1:617
Case B (plenum)
Plenum volume (h=0.40)
13,50m³
Plenum volume/Model internal volume ratio
1:8
Plenum inlet opening area
2.20m²
on-floor air diffuser opening area (Plenum outlet)
0.25m²
Plenum Inlet/Plenum outlet opening ratio
9:1
On-floor air diffuser /sawtooth roof outlet opening ratio
1:7.2
3.3.1. Inlet-outlet opening ratio and wall porosity
Inlet-to-outlet ratio and relative location of openings on a building façade are important
parameters to be considered, in addition to the wall porosity (Karava et al. 2011)
.
Internal pressure coefficients vary considerably with large opening area (wall porosity)
and the inlet to outlet ratio. The opening ratio is important for keeping a positive pressure
gradient inside the house. The principle criterion is keeping the positive pressure higher
at lower level spaces and near zero at the top of the house, at the leeward outlet
opening (see fig. 10). The inlet-outlet opening ratio for case A is 1:1. However, in case B,
the inlet-outlet opening ratio of the naturally pressurized plenum is 9:1. If we consider
three levels (plenum, room and outlet opening level), as we go up through levels 0, 1
and 2 the static pressure goes up to the upper leeward opening, at the top of the leeward
sawtooth roof, where the negative pressure module should be high as possible.
3.3.2. Envelope house and surfaces pressure coefficient
Increasing the pressure coefficient difference (
∆
)
of the building surfaces should be an
architectural strategy for leading the air stream throughout the building opening. Taking
advantage of the wind forces by adapting the building shapes, and integrating that with
the HVAC system when necessary, should be the main building envelope design criteria
in tropical weather for achieving thermal comfort. Under this precept, the main goal of
