8.8 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cross ventilation | 2/2 | https://en.wikipedia.org/wiki/Cross_ventilation | reference | science, encyclopedia | 2026-05-05T10:54:56.230155+00:00 | kb-cron |
Single-sided ventilation: This method depends on the pressure contrasts between different openings within the occupied space. For rooms that only feature a single opening, the ventilation is impelled by turbulence, thereby creating a pumping activity on that lone opening, causing small inflows and outflows. Single-sided ventilation has a weak effect. It is preferable when cross ventilation is not achievable, where it uses windows or vents at the other side of the space to control air pressure. Cross ventilation (single spaces): Being unsophisticated and efficacious, this type of ventilation is a horizontal process that is driven by pressure differences between the windward and leeward sides of the occupied indoor environment. Ventilation here is generally provided using windows and vents at either side of a building where the variation in pressure draw air in and out. Cross ventilation (double-banked spaces): Involving banked rooms, this method features openings in the hallway structure. The openings allow a way for noise to move between spaces. It can provide a much higher air-exchange rate in comparison with single-sided ventilation. Stack ventilation: This ventilation is a vertical process and it's beneficiary for taller buildings with central atriums. It draws cooler air in at a lower level, whereby the air rises thereafter due to heat exposure before it is ventilated out at a higher level. Benefits from temperature compartmentalization and related pressure quality of the air, whereby warm air loses density when it rises and the cooler air supplants it.
== Equation == For a simple volume with two openings, the cross wind flow rate can be calculated using the following equation:
Q
=
U
wind
C
p1
−
C
p2
1
/
(
A
1
2
C
1
2
)
+
1
/
(
A
2
2
C
2
2
)
(
1
)
{\displaystyle Q=U_{\textrm {wind}}{\sqrt {\frac {C_{\textrm {p1}}-C_{\textrm {p2}}}{1/\left(A_{\textrm {1}}^{2}C_{\textrm {1}}^{2}\right)+1/\left(A_{\textrm {2}}^{2}C_{\textrm {2}}^{2}\right)}}}\qquad {}\left(1\right)}
where
U
wind
{\displaystyle U_{\textrm {wind}}}
is the far-field wind speed;
C
p1
{\displaystyle C_{\textrm {p1}}}
is a local pressure drag coefficient for the building, defined at the location of the upstream opening;
C
p2
{\displaystyle C_{\textrm {p2}}}
is a local pressure drag coefficient for the building, defined at the location of the downstream opening;
A
1
{\displaystyle A_{\textrm {1}}}
is the cross-sectional area of the upstream opening;
A
2
{\displaystyle A_{\textrm {2}}}
is the cross-sectional area of the downstream opening;
C
1
{\displaystyle C_{\textrm {1}}}
is the discharge coefficient of the upstream opening; and
C
2
{\displaystyle C_{\textrm {2}}}
is the discharge coefficient of the downstream opening. For rooms with single opening, the calculation of ventilation rate is more complicated than cross ventilation due to the bi-directional flow and strong turbulent effect. The ventilation rate for single-sided ventilation can be accurately predicted by combining different models for mean flow, pulsating flow and eddy penetration. The mean flow rate for single-sided ventilation is determined by:
Q
¯
=
C
d
l
C
p
∫
z
0
h
−
2
Δ
P
(
z
)
ρ
d
z
z
r
e
f
1
/
7
U
¯
{\displaystyle {\bar {Q}}={\frac {C_{d}\;l\;{\sqrt {Cp}}\;\int \limits _{z_{0}}^{h}{\sqrt {-{\frac {2\;\Delta \;P(z)}{\rho }}}}\,\mathrm {d} z}{z_{ref}^{1/7}}}\;{\bar {U}}}
where l = width of the window; h = elevation of the top edge of the window; z0 = elevation of neural level (where inside and outside pressure balance); zref = reference elevation where the wind velocity is measured (at 10 m) and
U
¯
{\displaystyle {\bar {U}}}
= mean wind velocity at the reference elevation. As observed in the equation (1), the air exchange depends linearly on the wind speed in the urban place where the architectural project will be built. CFD (Computational Fluid Dynamics) tools and zonal modelings are usually used to design naturally ventilated buildings. Windcatchers can assist wind-driven ventilation by guiding air in and out of structures.
== See also == Windcatcher Passive cooling Passive ventilation Room air distribution Thermal comfort
== References ==