supply of fresh air removal of internal heat heat ......supply of fresh air removal of internal heat...
TRANSCRIPT
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Air flow
Ventilationsupply of fresh air
removal of internal heat
heat dissipation from skin
Image by MIT OCW.
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Air flow
Ventilationsupply of fresh air
removal of internal heat
heat dissipation from skin
![Page 3: supply of fresh air removal of internal heat heat ......supply of fresh air removal of internal heat heat dissipation from skin. Air flow Ventilation Zion National Park Visitor Center](https://reader033.vdocuments.site/reader033/viewer/2022041902/5e618e3c1a33546faf63f487/html5/thumbnails/3.jpg)
Air flow
VentilationZion National Park Visitor Center (National Park Service & NREL)
Images courtesy of the U.S. Department of Energy.
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Air flow
Active air flowSupply of fresh air based on renewal and change rates
Ventilation flow rate vr (m3/s) = V x N (nb of air changes per hour) / 3600Ventilation conductance qv (W/K) = 1200 (J/m3K) x vr = 0.33 x N x VVentilation heat flow: Qv = qv x ΔT
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Air flowActive air flow
Supply of fresh air based on renewal and change rates
Same 60 m3 room as studied for heat flow. Heat losses through façade due to conduction = 190 W
Losses due to air renewal (N = 0.7 h-1) ? What should N be for ventilation and conduction losses to be equal ?
J1
J2
Exterior façade
Image by MIT OCW.
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Air flowPassive air flow
Fluid mechanics: p + ρgh + ½ ρv2 = constant (Bernouilli)hydrostatics :
Δp = -Δhρgstack effect :
Δpi-e(h) = (h-hn)g(ρe - ρi)ρ(T) = ρ0 · p/p0 · T0/T
pi > pe -> air escapes
pe > pi -> air enters
P i(h=0)
n
Ti Te
pi > pe -> air escapes
pe > pi -> air enters
P i(h=0)
n
Ti Te
h
h
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Air flowPassive air flow
Fluid mechanics: p + ρgh + ½ ρv2 = constant (Bernouilli)hydrostatics : Δp = -Δhρg
stack effect : Δpi-e(h) = (h-hn)g(ρe - ρi)ρ(T) = ρ0 · p/p0 · T0/T ≈ 1.29 (kg/m3) · 273/T
hydrodynamics (wind) : Δp = -½ ρ Δv2, Venturi effect : S1v1 = S2v2
1
2
3 4
P3 ;V3
P1 ;V1P2 ;V2
P4 ;V4Pi
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Air flow
Passive air flowFluid mechanics
Pressure ↓ if speed ↑
Turbulent vs. steady flow+
_
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Air flow
Wind
Protected zoneProtected zone
Ascending and descending movements along facades Influence of relative heights
Image by MIT OCW.
Image by MIT OCW.
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Air Flow
Reading assignment from Textbook:“Introduction to Architectural Science” by Szokolay: § 1.1.4 + § 1.4.2
Additional readings relevant to lecture topics:"How Buildings Work" by Allen: Chap 11
“Sun Wind Light“ by Brown & DeKay: § 6 in Chap 1A