(PTSB) 03 - Sintak

PERENCANAAN TEKNOLOGI

& SISTEM BANGUNAN

(PTSB) 03

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2

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What is Ventilation?

the effects of air movement

within a building and between the building and the outdoors

[Hyde 2000, Roaf et al 2003]

Purposes and processes

(1) supplying of fresh air, removing CO

₂

, smells and other

contaminants

(2) remove some internal heat when T

_o

< T

_i

(3) promoting heat dissipation from the skin called physiological

cooling.

Fresh air supply per person  

CO  ₂   Vr  

Required fresh air supply per person

● Minimum ventilation rate (vr) for residential buildings 10 L/s per person

[Givoni 1976, Szokolay 2004]

● Indoor air change (ACH)

n>1 for reason of hygiene and health

n > 50 (day) and n > 10 as the second normal solution for warm humid climates;

n > 1 at the daytime or n > 10 at the nighttime for reason of cooling.

n = 30 for reason cooling ventilation in hot humid regions

n = 4.4 - 16.0 for acceptable indoor air quality with respect to odors

^{vr x 3600}

N = ---

V

Paradigm Pollution Sources

2050

2025 Personal aesthetics

People Buildings

Outside Environment

2000

Health, productivity, comfort

1975 Comfort (+Health) People + Buildings

1935

Comfort

People

1900

Contagion

Poison

Philosophy of Ventilation since 1800

Fanger (1996) after Spengler, D.J., et al. (2002)

Up to 0.25 m/s Unperceivable (feeling of stale air) 0.25 to 0.5 m/s Comfort

0.5 to 1.0 m/s Comfort and slightly perceivable 1.0 to 1.5 m/s Slightly annoying

Above 1.5 m/s Needs correction if comfort and productivity should be

Indoor air speed and its effects on comfort sensation

Driving forces

for designing natural ventilation

Wind Pressure

Entering air into openings and pass through the building from the high-pressure windward areas to the low-pressure downwind areas

Stack Pressure

imbalance in the pressure gradients of the

internal and external air masses which results in

a vertical pressure difference.

Sc  =  1,4  H   Sc  >  2,4  H  

1,4  H  <  Sc  <  2,4  H  

Wind Pressure

Single sided- ventilation

v (U_bh )  

Q_ss   wind ratio

0.35, 0.25 and 0.08 for β=0°, 60°, 90°

exposure value

0.47 and 0.67 for urban and suburban in tropical

hot humid regions

Q _ss    =  0.025.  A.  U _bh     Single sided ventilation

where

A = effective area of openings (m²) U_bh = air velocity (m/s)

Natural Ventilation Techniques

Cross Ventilation

c_p W  

c_p L  

v (U^bh)  

Q_CR   wind ratio

0.35, 0.25 and 0.08 for β=0°, 60°, 90°

exposure value

0.47 and 0.67 for urban and suburban in tropical

hot humid regions

Cross Ventilation

Natural Ventilation Techniques

Q _CR = 0.827. V. A _eff .c _e .√ Δ p _W

where

c_e = effectiveness coefficient of openings,

0.1 (windows in one wall), 1 (full cross ventilation) v = wind velocity (m/s),

∆P_w = wind pressure difference

A_eff = effective area:

A

_eff

= A

_in

+ A

_out

√A

²_in

+ A

²_out

 ∆

pw = pw (cpW + cpL)

Cooling effects of cross-ventilation affected by microclimate around a building

Akashi Mochida , Hiroshi Yoshino, Satoshi Miyauchi, Teruaki Mitamura (2006)

Case  0   Case  1   Case  2  

Cross  ven3la3on  rate  (m³/s)   0.38   0.32   0.48  

Avarage  of  indoor  air  temperature  (°C)   26.7   26.9   26.6  

Stack Pressure

A stack effect is developed as a result of

differences in air temperature, and hence air density,

between the inside and

outside of the building.

h

To

Ti

The study of active stack effect to enhance natural ventilation

 

Stack size 40 cm × 40 cm, location 2—doors closed

Stack size 40 cm × 40 cm, location 2—doors closed.

Solar Chimney

`enhanced stack effect`

1. Incoming solar radiation 2. Glass traps heat into 3. Cavity

4. Black metal (or high- density black

material for thermal storage overnight) 5. Radiant heat

6. Stimulated air up-draught ventilates room

7. In cold, draughty

conditions, insulated hatch is lowered.