rag 121 sains persekitaran 1e(e)

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RAG 121ENVIRONMENTAL SCIENCE 1

LECTURE 5

©Assoc.Prof.Ar.Dr.Hj.Abdul Majid Ismail

Website

http://www.hbp@usm.my/ventilation

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LECTURE 5 VENTILATIONFirman Allah

Diantara tanda-tandaNya, bahawa Dia mengirim angin sebagai khabar gembira dan supaya Dia merasakan rahmatnya kepadamu dan supaya belayar kapal dengan perintahNya dan supaya kamu mencari rezekiNya, mudah-mudahan kamu berterima kasih (kepadaNya).

(Surah Ar-Rum ayat 46)

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VENTILATIONOBJECTIVE

TO CREATE A SUITABLE/ACCEPTABLE MICRO-CLIMATE INSIDE A SPACE.

MICRO-CLIMATE MEANS: THERMAL ENVIRONMENT & AIR QUALITY

SUITABLE/ACCEPTABLE MEANS: COMFORTABLE & ATTAINED THE

REQUIRED QUALITY FOR HUMAN WELLBEING

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VENTILATION (DEFINITION)

OUTDOOR AIR ADMITTANCE EITHER INTENSIONALLY/UNINTENSIONALLY – TO DILUTE AIR POLLUTANTS (AIR CONTAMINANTS) IN A BUILDING.

MINIMUM AIR CHANGE IS REQUIRED TO CONTROL POLLUTION LEVEL.

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THE VENTILATION CONDITION IN A BUILDING – DETERMINING FACTOR OF THE HEALTH CONDITION, COMFORT & WELLBEING OF THE OCCUPANTS.

FROM THE CLEANLINESS ASPECT & AIR MOVEMENT, LEVEL OF VENTILATION HAVE A DIRECT EFFECT ON THE HUMAN BODY (PHYSIOLOGY).

VENTILATION ALSO AFFECT HUMAN BODY INDIRECTLY FROM THE EFFECT OF AIRFLOW ON AIR TEMPERATURE, HUMIDITY & BUILDING SURFACES.

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MAIN PURPOSE OF VENTILATION

1. TO RETAIN AIR PURITY (QUALITY) IN A SPACE – HEALTH VENTILATION.

2. PROVIDE THERMAL COMFORT – INCREASED HEAT LOSS FROM OUR BODY & PREVENT FORMATION OF ANY UNCOMFORTABLE CONDITION DUE TO EXCESSIVE HUMIDITY & STICKY SKIN – VENTILATION FOR THERMAL COMFORT.

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3. TO COOL DOWN BUILNDING’S STRUCTURE IF THE INDOOR TEMPERATURE IS HIGHER THAN OUTDOOR – VENTILATION FOR STRUCTURAL COOLING.

PRIORITY IN COMPLYING TO THE ABOVE THREE FUNCTIONS DEPEND ON THE LOCAL CLIMATIC CONDITION.

TO ACCOMMODATE THESE THREE FUNCTIONS, DETAILS OF BUILDING DESIGN ARE REQUIRED.

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HEALTH VENTILATION PROVIDE SUFFICIENT OXIGEN FOR

BREATHING, COOKING, & CARRYING OUT ACTIVITIES.

PREVENT ANY EXCESSIVE INCREASED IN CARBON DIOXIDE AND UNWANTED (BAD) SMELL.

TO EXPELL OUT WATER VAPOUR (TOILETS, KITCHEN ETC.)

REMOVAL OF COMBUSTION PRODUCTS & BREATHING / RESPIRATION.

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THE DEGREE OF EFFECTIVENESS OF ANY VENTILATION PROCESS DETERMINED BY THE TYPE OF OCCUPANCY, AMOUNT & TYPE OF ACTIVITIES.

THE EFFECT OF ANY UNWANTED SMELL SUCH AS BODY ODOUR, FOOD, CIGRATTE & ETC. MUST BE REDUCED THROUGH THE PROCESS OF DILUTION.

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HEALTH VENTILATION CAN EASILY BE ACCCOMPLISHED BY COMPLYING WITH THE REQUIREMENT OF (UBBL, 1984) AND CITY COUNCIL’S GUIDELINES

THE STUDY ON MINIMUM SIZE OF PERMANENT AND CONTROLABLE OPENINGS SUCH AS WINDOW, DOOR AND AIR WELLS (WILL BE COVERED IN ENVIRONMENTAL SCIENCE 2)

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THERMAL COMFORT VENTILATION

TO PREPARE A COMFORTABLE CONDITION INDOOR, INCLUDING PREVENTION OF UNCOMFORTABLE CONDITION SUCH AS SKIN STICKINESS.

REQUIRE HIGH “RATE OF FLOW”.ANY UNEVEN DISTRIBUTION OF

INDOOR AIR FLOW WILL REQUIRE ADDITIONAL AIR SPEED.

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INCREASE HEAT LOSS BY CONVECTION.

INCREASE EVAPORATION PROCESS.

THE RATE OF INDOOR AIR FLOW IS DETERMINED BY THE GEOMETRY OF SPACE AND LOCATION OF OPENINGS (DETAILS DESIGN).

THE HOTTER THE AIR TEMPERATURE, THE FASTER THE AIR / WIND REQUIRED TO ATTAIN THERMAL COMFORT.

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VENTILATION FOR STRUCTURAL COOLING THE DIFFERENCE IN INDOOR & OUTDOOR

TEMPERATURE DETERMINED BY: WALLS COLOUR (DARK – HIGHER INDOOR

TEMPERATURE THERMAL CAPACITY, RESISTIVITY &

TEMPERATURE DIFFERENCE. WHEN OUTDOOR AIR ENTERS IT FORCES OUT

THE INDOOR HOT AIR. THE METHOD IS ONLY EFFECTIVE IF THE

DIFFERENCE IN OUTDOOR & INDOOR TEMPERATURE IS HIGH.

THE PROCESS TAKEN PLACE THROUGH CONVECTION

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METHOD OF VENTILATION

PASSIVE OR NATURAL VENTILATION EFFECT OF WIND PRESSURE STACK / CHIMNEY EFFECT

MECHANICAL VENTILATION FANS AIR-CONDITION

PASSIVE METHOD IS ALSO CAPABLE OF PROVIDING FRESH AIR AND COOLING TO THE BUILDING OCCUPANTS AT CERTAIN TIME AND AT SPECIFIC LOCATION.

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EFFECT OF WIND PRESSURE VENTILATION DESIGN INVOLVED:

DETERMINING THE SIZE, LOCATION OF OPENINGS SUCH AS WINDOW, CHIMNEY, LOUVRES, WIND HOLES ETC.

THE EXTERIOR PART OF THE BUILDING EXPERIENCING EITHER PRESSURE AND SUCTION.

THE PRESSURE DIFFERENCE BETWEEN EXTERIOR AND INTERIOR SECTION OF A BUILDING CREATES WIND / AIR FLOW ACROSS BUILDINGS.

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EFFECT OF WIND PRESSURE

+

-

-PRESURE SUCTION

SUCTION

INLET OPENING OUTLET OPENING

CROSS WIND FLOW

WIND

WIND

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WIND FLOW CAN BE CULCULATED USING THE FOLLOWING FORMULA: PW = 0.5 CP V2

= 0.162 V2

THEREFORE: PW = WIND PRESSURE (Pa / N/m2) CP = PRESSURE COEFFICIENT = AIR DENSITY ( 1.2 kg/s@200C) V = WIND VELOCITY (m/s)

WIND FLOW (PATTERN & SPEED), INFLUENCED BY THE OUTDOOR CONDITION.

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OUTDOOR WIND FLOW PATTERN (PLAN)

PRESSURE INCREASES PRESSURE

(SUCTION) REDUCES

VELOCITY INCREASES

LAMINAR FLOW

+ -

-

-

AREA OF WIND SHADOW

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FACTORS WHICH INFLUNCE INDOOR AIR FLOW

ORIENTATION EXTERNAL BARRIER CROSS VENTILATION LOCATION OF OPENINGS SIZE OF OPENINGS CONTROL OF OPENINGS

ORIENTATION APPROXIMATE WIND DIRECTION & SPEED

CAN BE OBTAINED FROM WIND CHART / LOCAL CLIMATE.

ORIENTATE MAIN / LARGEST OPENINGS TOWARDS PREVAILING WINDS.

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WIND COMING FROM AN OBLIQUE DIRECTION (450), CAPABLE OF INCREASING THE SPEED AND FAIR DISTRIBUTION INDOOR COMPARE TO PERPENDICULAR DIRECTION (900).

900 450

PERPENDICULAR OBLIQUE

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EXTERNAL BARRIER WIND SPEED INCREASES IF THERE

ARE BARRIER (TUNNELLING EFFECT)

SPEED INCREASES

BARRIER

BARRIER

BARRIER

SPEED INCREASES

PLAN SIDE ELEVATION

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SPACING BETWEEN BUILDINGS IS IMPORTANT (5 X HEIGHT)

H

5 X H

WIND FLOW OBSTRUCTED

ACCEPTABLE SPACING

1 2

21

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CROSS VENTILATION IF ROOMS ARE NOT PROVIDED WITH

OUTLETS OR FULL PARTITIONED, THERE WILL BE NO CROSS AIR FLOW. THEREFORE, OPENINGS MUST BE PROVIDED AS OUTLET TO AIR FLOW.

NO OUTLET OPENING PARTITION & NO OUTLET OPENINGS

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LOCATION OF OPENINGS OPENING MUST BE ABLE TO DIRECT THE

WIND FLOW TO THE “LIVING ZONE” / BODY, AT A HEIGHT OF 2m.

IF INLET OPENINGS ARE LOCATED AT THE TOP PART OF THE WALL, WIND FLOW WILL BE DIRECTED UPWARD.

IF INLET OPENINGS ARE LOCATED AT THE LOWER SECTION OF THE WALL, WIND FLOW WILL BE DIRECTED TOWARDS THE FLOOR.

OPENINGS ARE ADVISIBLE TO BE LOCATED AT THE MIDDLE SECTION OF THE WALL SO THAT THE AIR FLOW IS PARALLEL TO THE EXTERNAL WIND FLOW.

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LOCATION OF OPENINGS

ALIRAN KE ATAS

FLOW DIRECTED TOWARD “LIVING ZONE”/ BODY

WINDOW AT THE TOP

WINDOW IN THE MIDDLE

LIVING ZONE

LIVING ZONE

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SIZE OF OPENINGS HIGHER AIR SPEED CAN BE ACHIEVED

BY DESIGNING A SMALLER INLET OPENING & LARGER OUTLET OPENING (VENTURI EFFECT).

IF INLET OPENING IS LARGER, THE SPEED BECOME SLOWER, BUT FLOW PATTERN BECOME MORE UNIFORM (AIR FLOW DISTRIBUTED THROUGHOUT THE WHOLE ROOM).

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EXAMPLE: WIND SPEED OUTDOOR = 100% DIRECTION OF WIND FLOW = 450

450

450

SMALL INLET OPENING

LARGE OUTLET OPENING

LARGE INLET OPENING SMALL OUTLET OPENING

MAXIMUM SPEED = 152%

MAXIMUM SPEED = 76%

MEAN SPEED = 44%

MEAN SPEED = 42%

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CONTROL OF OPENINGS INDOOR AIR FLOW INFLUENCED BY THE

PRESENT OF OVERHANG, INTERNAL & EXTERNAL SHADING DEVICES & ETC.

FLOW UPWARD

FLOW DOWNWARD

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STACK / CHIMNEY EFFECT DETERMINED BY THERMAL POWER,

OCCUR WHEN THERE ARE LARGE DIFFERENCES IN AIR TEMPERATURE INDOOR AND OUTDOOR.

IF THERE ARE WINDOOWS OR OPENINGS, HOT AIR WILL RISE UP & EXPELLED THROUGH THE TOP OPENINGS.

COOL & FRESH AIR ENTER FROM THE LOWER OPENING REPLACING THE VACANCY CREATED BY THE HOT AIR (SAMILAR PRINCIPLE AS THE FORMATION OF WIND).

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THE PROCESS DEVELOPED AND FORMED A NATURAL INFLOW & OUTFLOW OF AIR.

THE RATE OF VENTILATION CAN BE CULCULATED USING THE FORMULA BELOW: V = 0 117 x A x h 0.5 x t (m3/sec/m2)

ti

to

HOT AIR FLOW OUT

COLD AIR FLOW IN

h

t = to –ti

AREA OF INFLOW OPENINGS = A

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CORRECTION FACTOR Ai = AREA OF INLET OPENING Ao = AREA OF OUTLET OPENING

IF SIZE Ai & Ao VERY DIFFERENT MULTIPLY ‘V’ WITH cf VALUE FROM TABLE

Ai/Ao cf

5 1.38

4 1.37

3 1.33

2 1.26

1 1.0

0.75 0.84

0.5 0.63

0.25 0.34

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EFFECTIVENESS OF NATURAL VENTILATION

DETERMINED BY CLIMATIC ELEMENTS (TEMPERATURE & WIND)

DESIGN FACTORS WHICH ARE UNDER THE CONTROL OF AN ARCHITECT REQUIRE PRELIMINARY STUDY ORIENTATION, SIZE, LOCATION, TYPE OF

CONTROL NEED TO BE INTEGRATED WITH THE

OVERALL BUILDING SYSTEM IF THE PERFORMANCE IS LESS

EFFECTIVE, ADDITIONAL AIDS CAN BE INCORPORATED BUT NOT OTHERWISE.

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VENTILATION & AIR QUALITY

CONSIDERATION HAS TO BE GIVEN TO THE AMOUNT OF AIR REQUIRED TO EXPELL USED AIR, TO CONTROL HUMIDITY, CARBON DIOXIDE AND SMELL.

MAINTAINING CARBON DIOXIDE (CO2) LEVEL IS A COMMON CRITERIA IN DETERMINING THE VENTILATION RATE.

COMMON VALUE - 5.3 mL/s

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CO2 CONCENTRATION IS GIVEN BY: Ci = Co + F/Q WHERE:

Ci = CO2 concentration indoor

Co = CO2 concentration outdoor

F = rate of CO2 formation, L/s Q = rate of ventilation (outdoor air only), L/s

RATE OF VENTILATION PER PERSON: Q = F/(Ci – Co )

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RATE OF VENTILATION PER PERSON TO RETAIN CO2 LEVEL ABOVE CL LEVEL IS: Q = (0.0053 X 100) / [CL(%) - CO(%)]

NORMAL OUTDOOR CO2 LEVEL = 0.03% ASHRAE Standard ventilation for this

purpose is 7.5L/s of outdoor air per person for CO2 0.1L/s. Normal human being can accept CO2 level up to 0.5%.

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REMINDER CONFLICT IN THE SELECTION OF THE

TYPE OF ENVIRONMENTAL CONTROL: IF PASSIVE METHOD IS SELECTED –

MECHANICAL AID SUCH AS FANS ARE REQUIRED TO BE USED ONLY WHEN THERE ARE INSUFFICIENT WIND SPEED & DISTRIBUTION TO CREATE COMFORTABLE CONDITION INDOOR.

IF A/C IS SELECTED – PASSIVE AID SUCH AS OPENABLE WINDOWS ARE NOT REQUIRED – WINDOWS SHOULD BE TOTALLY CLOSED TO PREVENT ANY LEAKAGES OF COOL AIR FLOWING OUTWARD.

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TEST 1:TUESDAY 25.8.09

VENUE: L17- DEWAN PELAJAR C (OPPOSITE PADANG KAWAD)

TIME: 2:30 – 4:30 PM

TERIMA KASIH & GOOD LUCK