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Definition
- Process by which stale (not fresh) air in an
enclosure is replaced by fresh air from
outside.- replacement of used inside air by outside
air.
- measured by the number of air changes per
hours or volume changes per unit time (m3/h).
Purpose Health & survival
- Comfort
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For breathing (i.e. inhaling O2&
exhale CO2)
Prevent growth of fungus or mold
Remove bacteria, fumes & bad
odour
Enable our bodies to lose heat
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a) Supply fresh air to remove and replace gases such
as carbon dioxide, humidity, water vapors, dust,fumes, smoke etc. Requirement of fresh air supply
are governed by type, number of occupants and
activity carried out in the space.
b) Convective cooling to remove excessive heat andstructural cooling. The exchange indoor air with
fresh out door air can provide cooling. The moving
air acts as a heat carrying medium : stack effects.
c) Physiological cooling to gain human comfort (known as air movement). Air movement accelerates
heat dissipation through skin in 2 ways : increasing
convective heat loss and accelerating evaporation.
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1)
Natural Caused by air motion due to temperature &
pressure differences
Wind becomes of great importance where
natural ventilation is concerned.
E.g. stack effects (warm air rises & the space
left behind is filled or replaced by cool air),
wind pressure
Characteristics of wind:
- wind speed is reduced near ground
- movement vary depending on topography
- acceptable = 5 m/s
- unpleasant = 10 m/s
- dangerous => 20 m/s
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Any building ventilation system involves 4 basiccomponents :-
a) A source of air : acceptable temperature, moisturecontent and cleanliness.
b) A force to move air through the inhabited space of
the building either or both of 2 motive forces (highpressure area to lower - pressure area) may beemployed for natural ventilation : wind poweredventilation and convection ventilation.
c) A means of controlling the volume, velocity and
direction of air flow: windows and opening, roofventilator, roof moisture, opening skylights, airbrick, fencing, plant / landscaping.
d) A means of recycling or disposing of contaminatedair e.g : chimney, air well.
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AIR CHANGE:-
1) When the volume of air in an enclosure diluted
or replaced by an equal volume of fresh air, oneair change has taken place.
2) The number of air changes per hour requireddepends on occupancy rate and type activitiescarried out in the building or part therefore.
3) The recommended number of air changes varyfrom 3-12 air changes per hour for residentialbuildings. The number is generally for livingand bedroom.
4) Infiltration- the passage or exchange of airthrough cracks causes up to 15 air changes perhour.
- The helps in air change of a room.
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i) Air movement some degree of air movement isessential for feeling of freshness and comfort. The
required speed of wind various with temperature. A
velocity 5-10 m/s is acceptable but not more.
ii) Body odour to keep body odour at the controlled level.
iii) Preventing bacteria growth which is greatly increasedin damp and stale air.
iv) Excess heat caused loses of body fluid and may result in
exhaustion. Sufficient amount of air movement stabilizes
this situation.
v) Relative humidity (RH) RH of 30% to 70% for acomfortable atmosphere. RH exceeds than 70% result in
condensation. High rate of ventilation is advised when
RH exceed 70% limit.
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1) To ensure cross-ventilation by having opening on
opposite walls to a maximum of 30% of floor area.
2) Trees lined would reduced the prevailing wind
speed, deflect and acts as filter medium of air.
3) Location of building to give advantage of relief andprevailing wind condition on the slope facing wind.
4) Choice of building material which are porous to
help in improving natural ventilation.
5) Design of roof structures with opening will result inbetter ventilation.
6) Presence of water bodies will bring about stack
effect this improving ventilation.
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2) Artificial
Caused by mechanical or artificial
forces
E.g. propeller fans, roof ventilator
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Why Artificial Ventilation?
i) Internal rooms ( where theres no window at all)
ii) Large, closely populated rooms where distributionof natural ventilation would be inadequate.
iii) In cases where specially controlled environment isrequired particularly in relation to RH and dustparticles in the air.
iv) Rooms where volume per occupants is to low forefficient natural ventilation.
v) Where natural ventilation is impossible as windowcant opened because of external atmosphere, i.e.pollution and noise.
vi) In tall buildings, where wind and stack effectrender natural ventilation impracticable.
vii) Extract ventilation may be required to deal withfumes or smells from cooking and other specialprocesses.
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3 types of fans used in mechanical ventilation :-
a) Propeller fan
suitable for situation where theres no great resistanceto air flow to be overcome.
b) Axial flow fan
popular
has high frequency, high efficiency, simple installation andneat appearance
can be aligned in line or ducting number of blades are many and small
less noise is generated
c) Centrifugal fan
develop sufficient pressure to drive air through thetreatment plant duct system
Output of the fan can be varied by different motor andspeed operation, bulky and turns directions of air through90
Used for tunnel
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Definisi : Proses perawatan udara untuk ruang-ruang atau tempat-tempat tertutup. Perawatan
dilakukan terhadap suhu udara, kelembapan
udara, gantian udara, kebersihan udara dan
pengagihan udara bagi mencapai keperluan-keperluan tertentu di mana ruang-ruang ia
berfungsi.
Suhu Pemanasan / PenyejukanKelembapan Humidification/DehumidificationKebersihan Penapis,penyucian,peresapan kotoranPengagihan Pengudaran dan cara pengagihan
Keadaan udara yang diperlukan
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Keselesaan
Prestasi kerja
Kesihatan
Peralatan komputer Simbol status
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a) Menghalang bunyi bising daripersekitaran
b) Menghalang habuk dan kotoranc) Mengeluarkan haba berlebihan untuk
keselesaand) Mendapat pengudaraan yang cukupe) Mengawal kelembapanf) Menghalang bau-bau yang tidak diinginig) Mengagihkan udara
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a) Orientasi bangunan
Luas penutupan dan pembukaan bangunan
terhadap pergerakan matahari.
b) Penutupan bangunan
Kecepatan pergerakan haba dan faktor
simpanan
c) Penyusupan
Permukaan yang terbuka/berlubang akanmenentukan udara yang masuk
d) Keadaan persekitaran
e) Aktiviti dan alatan dalam ruang.
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1) Cooling load (beban penyejukan)
2) Air-handling load (muatan kendalian udara)
3) Machine power (kuasa kejenteraan)
4) Energy & power (tenaga & kuasa)
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1) Beban penyejukan
Definasi: Suatu konsep yang digunakanuntuk menghitung beban atau kekuatan
dan keupayaan alat penyaman udara
bagi menyejukkan udara pada proses
refrigeration. Unit : btu/hour (british thermal
unit/hour)
1 watt = 3.412 btu/hour
1 kaki2ruang : 60-100 btu/hour untuk
keadaan normal (0.093 m2)
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2) Muatan kendalian udara
Definasi: Dikaitkan dengan banyaknya udara
bekal yang akan dikendalikan oleh kipasdalam pusingan udara.(Keupayaan kipasuntuk mengatasi rintangan)
Unit : CFM Cubic feet per minute (m3/s )
1 m3
/s = 35.3 CFM3) Keupayaan kejenteraan
Mengukur keupayaan mekanikal:-i) Kuasa motor ( 1 hp = 7457 waat)
ii) Pam
4) Kuasa dan Tenaga
Menentukan sambungan elektrik daripadasistem
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a) Bukan semua keadaan yang dibekalkansesuai.
b) Suhu yang digunakan sesuai untuk badan
manusia
Suhu optima = +37 C
c) Kelembapan relatif = 40 60%
d) Pergerakan udara tidak melebihi 39
kaki/min atau 12 m / minit.
e) Bekalan udara yang bersih
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Prinsip Penyaman udara
Berdasarkan kepada sifat jisim, haba danrefrigeration
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Adalah untuk mengeluarkan, mengalirkan haba
dari 1 tempat ke tempat yang lain. Berdasarkan
kepada 2 sifat jirim:-
a) Bendalir menyerap haba apabila bertukar
daripada cecair kepada gas
b) Bendalir mengeluarkan haba apabila gas
bertukar kepada cecair.
Terdapat 2 jenis kitaran hawa dingin:-
a) Kitaran Refrigerant
b) Kitaran udara
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Satu proses penyejukan iaitu mengalirkan
haba dari satu tempat ke satu tempat
yang lain dengan satu media pembawahaba.
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Untuk mengalirkan haba dari ruang yang
didinginkan serta memberi pengudaraan,
haba dialirkan melalui alat pengewapan
dalam loji penyaman udara.
Dari ruang
Ruang/bilik
Pemindahan haba
Evaporator
Ke udara luar
Condenser
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Refrigerator system with A refrigerator,
B compressor, C expansion valve with
liquid ammonia
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Dlm kitaran udara, terdapat 10 komponen yg perlu
diketahui sebelum sesuatu loji tersebut beroperasi:-
a) Kipasutk mengerakkan udara dlm 1 kitaran udara.
b) Saluran udara bekal mengagihkan udara dr tempatrawatan ke ruang yg hendak dinyamankan
c) Salur masuk mengalirkan udara di dalam ruang
untuk keselesaan
d) Ruang (bilik) Ruang yang tertutup.e) Saluran balik membawa udara balik ke loji.
f) Saluran udara balik Ducting khas yang membawa
udara ke loji
g) Lingkaran penyejukan untuk mengeluarkan habadari dalam ruang
h) Pembuangan udara kotor
i) Pengambilanpengambilan udara luar untuk (Bilik
AHU) proses pengudaraan ( tambahan oksigen)
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Sistem unit
Unit tingkap Unit kemas siap Unit pisah
Keseluruhan Penyejukan
udara
Penyejukan
air
Tanpa udara Dengan udara
Sistem Loji
Loji berpusat Air disejukkan(chiller)
Terbahagi kepada 2:-
1) Sistem unit2) Sistem loji pusat
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Sesuai digunakan bagi ruang yang kecil dan
sederhana.
Luas lantai yang sesuai ialah 5-300 m2
Beban : < 360, 000 BTUH
Kendalian : < 6000 CFM
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Luas lantai yang boleh digunakan ialah < 25m2
Terdapat 2 pemampat :-
i) Pistonii) Rotary
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i) Keseluruhan
sesuai untuk keluasan lantai 25- 220 m2. Beban diantara24,000 270,000 BTU/H.
Ianya seperti unit tingkap kecuali tidak dipasang padatingkap (dipasang di luar rumah atau bangunan).
Udara disalur ke dalam ruang dengan menggunakansaluran (ducting).
Besar sedikit dari unit tingkap.
ii) Penyejukan udara
Beban penyejukan dan kemasan keseluruhan 25,000-360,000 BTU/H.
Luas lantai ialah 20-300 m2
. Condenser berada di luar bangunan sementara
evaporator berada dalam 1 unit yang lain.
Compressor dan injap boleh berada di luar atau dalambangunan bergantung kepada pembekal dari kilang
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iii) Penyejukan air
Air digunakan untuk menyejukkan condenser. Kos pembaikannya lebih tinggi sebab
compressornya mahal.
Kebaikkanya ilaha sekiranya 1 unit rosak, unit-
unit pada bahagian lain boleh digunakan. Beban penyejukan : 21,000 490,000 BTU/H
Luas lantai : 17 400m2
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Terdapat 2 sistem yang digunakan :-
i) Tanpa udaraii) Menggunakan Udara luar
i) Tanpa udara
Condenser dan evaporator terasing
Piping jenis tembaga digunakan untuk membawamedia pembawa haba (gas) dari condenser keevaporator.
Seperti unit kemas-siap, beban yang sesuai ialah6000-24,000 BTUH.
ii) Udara luar
Beban penyejukannya ialah : 46,000-290,000 BTUH
Keluasan lantai : 40-240 m^2
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a) Loji Berpusat
Melibatkan beban penyejukan yang lebihbesar (15 ribu ton refrigerant).
b) CHILLER
Air digunakan sebagai bahan
penyejukan. Air yang telah disejukkan
dalam chiller di hantar semula ke dalam
bilik AHU
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1) The compressor which pumps the refrigerant around the
system, is the heart of air-conditioner. Before the compressor,the refrigerant is a gas at low pressure, because of the
compressor, the gas becomes high pressure, get heated and
flows towards the condenser.
2) At the condenser, the high temperature, high pressure gas
releases it heats to the outdoor air and becomes subcooled
high pressure liquid.
3) The high pressure liquid goes to the expansion valve, which
reduces the pressure and thus the temperature goes below the
temperature of the refrigerated space.This results in cold andlow pressure refrigerant liquid.
4) The low pressure refrigerant flows to the evaporator where its
absorbs heat from the indoor air thought the evaporation and
becomes low pressure gas. The gas flows back to the
compressor where the cycle starts all over again.
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Window unit
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Air-cond
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PEMASANGAN INDOOR UNIT
Mestilah pada tempat yang kukuh.
Mempunyai peredaraan udara yang baik.
Jauhkan dari punca-punca haba.
Saluran air keluar (drain) mudah.
Kesan bunyi dan gegaran
Penyambungan dan panjang pemaipan mengikut spesifikasi
* PASTIKAN ANDA MENGGUNAKAN 2 SPANAR UNTUK
MENGETATKAN PENYAMBUNGAN PEMAIPAN
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ELAKKAN DARIPADA MELAKUKAN PERKARA-PERKARA DI BAWAH:
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PEMASANGAN OUTDOOR UNIT
Pasang pada tempat yang kukuh.
Pembebasan haba tidak terhalang.
Elakkan mudah di gapai oleh kanak-kanak.
Mudah melakukan pembaikan/penyelenggaraan.
Penyambungan dan panjang pemaipan mengikut spesifikasi.
Melakukan Purging setelah pemaipan disambungkan.
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