HVAC Course

HVAC Course

Dr. Eng. Ahmed Rezk Assistant professor Alexandria University

1

Introduction • Definition: it is the process of altering the air properties (temperature, humidity, quality and distribution) to more favorable conditions. Air conditioning can refer to cooling, heating, ventilation or disinfection, that modifies the condition of air. • Atmospheric air always contains water vapor. The content of water vapor in air also plays an important role in comfort air-conditioning. 2

Air conditioning systems (HVAC (HVAC) AC) Open discussion Air conditioners

Room AC

Evaporative coolers

Central AC

DX systems

Hydronic system

Package units

Split units

Using high wall FCU

Using - AHU

Using - VAV

Using - AHU

Using C - C FCU

3

Air properties • Psychrometry: The science which deals with the study of the behavior of air and water vapor mixture is known as psychrometry. The properties of water vapor and air mixture are known as psychometric properties. • Dry air: The mixture of nitrogen and oxygen neglecting the water vapor and other gases is known as dry air. 4

Air properties • Moist air: It is a mixture of dry air and water vapor. The quantity of water vapor present in air depends upon the temperature of the air. • Moisture: The water vapor present in the air is known as moisture and its quantity in air is an important factor in all airconditioning system.

5

Air properties • Dry bulb temperature: The temperature of air measured by ordinary temperature thermometer is known as dry-bulb temperature. • Wet bulb temperature: The temperature recorded by a thermometer when its bulb is covered with wet cloth and is exposed to a current of moving air is known as wet bulb temperature. • Dew point temperature: it is the temperature at which the air can no longer "hold" all of the water vapor which is mixed with it, and some of the water vapor must condense into liquid water. 6

Air properties • Specific humidity (humidity ratio): It is the weight of water vapor present per kg of dry air. • Relative humidity: It is defined as the ratio of actual weight of water vapor in a given volume to the weight or water vapor contained in the same volume at the same temperature when the air is saturated. • Sensible heat of air: The quantity of heat that can be measured by measuring the dry bulb temperature of the air. • Total heat: The total heat of the humid air is the sum of the sensible heat of the dry air and latent heat of water vapor associated with dry air. 7

Air properties

Comfort Zone

8

Psychrometric processes

Humidification Heating and humidification Adiabatic humidification Sensible heating

Sensible cooling

Adiabatic dehumidification Cooling and dehumidification Dehumidification 9

Psychrometric processes • Cooling and dehumidification: It can be achieved by using cooling coil of surface temperature below dew point temperature. That to allow water vapor in the air to be condensed.

Room Air Supply Air

10

Psychrometric processes Conditioned air production • The supply air can be reconditioned after removing the space load (all return), it can be mixed with fresh air to reduce the space air contamination (mixed), or we can use totally fresh air in special requirements (all fresh).

11

Outside Air

Room Air Supply Air

Outside Air

Mixed Air Room Air Supply Air 12

Psychrometric processes (humid summer) 1

• Cooling coil capacity [ CCC ] S

• Amount of condensate [ mw ]

2

• Sensible heat factor [ SHF ] • Bypass factor [ BPF ]

13

Psychrometric processes • Sensible heating: the heating can be achieved by electrical heaters, steam, hot water coil or heat pumps. • Sensible cooling: It can be achieved by cooling coil of surface temperature higher than the dew point temperature (where no water vapor condensation). The cooling coil could be DX coil or chilled water coil. 14

Psychrometric processes • Humidification: it can be produced by supplying saturated steam at a temperature equal to dry bulb temperature of the air. • Adiabatic dehumidification: It is a special process that can be done DESCICANTS (ex, Silica gel). • Adiabatic cooling: It can be done by direct contact between water (droplet in air washer or mist in ultrasonic mist maker) and air. 15

Psychrometric processes

16

Comfort requirements not only temperature and humidity control. control. • Minimum fresh air requirements. • Lighting density. • Air distribution and velocity. • Noise level (30-55 db). • Furniture and work space layout.

17

Cooling load calculation • The cooling load calculations have to be done very accurate, not to overestimate or underestimate the required systems capacities. The following parameters are required for cooling load calculations: • • • • • • • •

Building drawings including the geographical directions. Rooms dimensions and applications. Structure materials. Windows and doors areas. Rooms occupancy. Lighting type and distribution. Appliances available in the space Infiltration sources. 18

Cooling load calculation • Methods of cooling load calculations • Using estimated load per surface area based on applications. • Accurate manual calculations. • Using Hourly Analysis Program (HAP).

• Ton of refrigeration: A ton of refrigeration (commonly abbreviated as TR) is a unit of power used to describe the heat-extraction capacity of refrigeration and air conditioning equipment. 1 TR = 3.517 kW = 12,000 BTU/h

19

Cooling load calculation (Manually) • Load components • Transmission load through walls, celling and roof. • Solar heat gain. • Heat gain through windows, and doors. • Occupants heat gain (sensible, latent). • Appliances heat gain (sensible and latent). • Light heat gain. • Ventilation load (sensible and latent). • Infiltration load (sensible and latent). 20

Cooling load calculation (Manually) • Outside design conditions • You can get the information from the ASHRAE or using Weather Underground website. (http://www.wunderground.com/q/zmw:00000.1.62318?)

• Inside design conditions. • Inside dry bulb temperature and relative humidity are depend on the application. • • • • •

residential (24°C / 50%) Textile (24°C / 65%) Printing (27°C / 45%) Sweets (25°C / 33%) Leather (32°C / 75%) 21

‫)‪Cooling load calculation (Manually‬‬ ‫‪• Transmission load through walls, celling, roof and doors.‬‬ ‫  ‪
 =   −‬‬ ‫‪1‬‬ ‫‪1‬‬ ‫‬ ‫‪1‬‬ ‫=‬ ‫‪+ +‬‬ ‫‬ ‫‪ℎ‬‬ ‫‬ ‫ ‪ℎ‬‬

‫اتجاه الحرارة‬

‫‪h‬‬

‫نوعية السطح‬ ‫أ ـ ھواء ساكن‬

‫أفقي‬

‫إلى أعلى‬

‫‪10‬‬

‫أفقي‬

‫إلى أسفل‬

‫‪6‬‬

‫رأسي‬

‫أفقي‬

‫‪8‬‬

‫ب ـ ھواء متحرك‬

‫‪22‬‬

‫بسرعة ‪ 6.7‬متر‪/‬ثانية‬

‫أي اتجاه‬

‫‪34‬‬

‫بسرعة ‪ 3.4‬متر‪/‬ثانية‬

‫أي اتجاه‬

‫‪23‬‬

Cooling load calculation (Manually) K

0.72

• Transmission load through walls, celling and roof. • U= overall heat transfer coefficient (W/m2k) • K= thermal conductivity (W/mk) • h= convective heat transfer coefficient (W/m2K)

Material (Common brick)

‫طوب عادي‬ ‫طوب واجه‬

1.30

(Face brick)

1.72

(concrete)

1.10

(Tiles)

1.80

(Stone)

0.72

(Cement plaster)

‫مونة اسمنتية‬

0.80

(Gypsum plaster)

‫مونة جبسية‬

0.16

(Hard wood)

‫خشب ناشف‬

0.12

(Soft wood)

‫خشب طري‬

1.72

(Sand)

‫رمل‬

0.036

(Cork)

‫فلين‬

0.036

(Glass wool)

0.040

(Polystyrene)

0.023

(Polyurethane)

0.79

(Glass)

‫خرسانة‬ ‫بالط‬ ‫حجارة‬

‫صوف زجاجي‬ ‫بولسترين‬ ‫بولي اريسان‬ ‫زجاج‬ 23

Cooling load calculation (Manually) • Solar heat gain • Solar heat gain is due to solar radiation. • Part of the solar radiation will be absorbed and the other will be reflected.


 =  ∆ ∆

 = ℎ

α 0.7 – 0.55

‫مادة السطح‬ ‫طوب أحمر رملي جيري‬

0.5 – 0.4

‫طوب أبيض رملي جيري‬

0.5 – 0.3

‫حجارة جيرية‬

0.65

‫بالط خرساني‬

0.9

‫سقف أسفلتي‬

0.9 – 0.8

‫اردواز رمادي‬

• I= max solar radiation intensity based on wall direction (tabulated) • α= surface solar radiation absorptivity. 24

Cooling load calculation (Manually) • Heat transmission through glasses • Glass Load Factor (GLF) method.
 =  ∗  !" #$%# • GLF based on window type and direction (ASHRAE)

25

Cooling load calculation (Manually) • Heat transmission through glasses • Normal method.


 = &' ∗  ∗  −  • For shade coefficient (SC) and Ug (ASHRAE)

26

‫)‪Cooling load calculation (Manually‬‬

‫حالة اإلنسان‬

‫‪• Occupants heat gain: Heat gain due to people activities.‬‬ ‫المجموع‬ ‫حرارة‬ ‫حرارة‬ ‫‪•
(, = *+ ∗
/+‬‬ ‫االستخدام‬ ‫‪W‬‬ ‫محسوسة ‪W‬‬ ‫محسوسة ‪W‬‬

‫جالس ومستريح‬

‫مسرح‬

‫‪66‬‬

‫‪31‬‬

‫‪97‬‬

‫جالس ويعمل عمل خفيف‬

‫مكتب ـ شقة ـ فنقد‬

‫‪72‬‬

‫‪45‬‬

‫‪117‬‬

‫يزاول عمل متوسط‬

‫مكتب ـ شقة ـ فندق‬

‫‪73‬‬

‫‪59‬‬

‫‪132‬‬

‫واقف ويزاول عمل خفيف‬

‫محالت تجارية‬

‫‪73‬‬

‫‪59‬‬

‫‪132‬‬

‫يمشي ببطء‬

‫بنك‬

‫‪73‬‬

‫‪73‬‬

‫‪146‬‬

‫جالس‬

‫مطعم‬

‫‪81‬‬

‫‪81‬‬

‫‪162‬‬

‫يزاول شغل بسيط‬

‫مصنع‬

‫‪81‬‬

‫‪139‬‬

‫‪229‬‬

‫عامل متحرك‬

‫مصنع‬

‫‪110‬‬

‫‪183‬‬

‫‪293‬‬

‫عامل يزاول شغل متوسط‬

‫مصنع‬

‫‪88‬‬

‫‪204‬‬

‫‪292‬‬

‫عامل يزاول شغل ثقيل‬

‫مصنع‬

‫‪170‬‬

‫‪255‬‬

‫‪425‬‬

‫شخص يزاول رياضة‬

‫ملعب‬

‫‪170‬‬

‫‪255‬‬

‫‪425‬‬

‫‪27‬‬

‫‪•
(,- = *+ ∗
-/+‬‬

‫)‪Cooling load calculation (Manually‬‬ ‫)‪• Lighting load (sensible only‬‬ ‫‪
 . = /ℎ0  0% 102 ∗ 3""$ $%#‬‬ ‫نوعية المبنى‬ ‫مكاتب‬

‫‪28‬‬

‫شدة اإلضاءة‬ ‫‪60‬‬

‫مصانع‬

‫‪45‬‬

‫مدارس ـ جامعات‬

‫‪40‬‬

‫شقة ـ مدرج ـ مسرح ـ فنادق‬

‫‪20‬‬

‫مطاعم‬

‫‪17‬‬

‫مستشفيات ـ مكتبات ـ متاحف‬

‫‪15‬‬

‫)‪Cooling load calculation (Manually‬‬ ‫)‪• Appliances heat gain (sensible and latent‬‬ ‫نوع الموقد‬

‫بدون ھود‬ ‫حرارة كامنة‬ ‫حرارة محسوسة‬

‫مع ھود‬ ‫حرارة محسوسة‬ ‫‪150‬‬

‫موقد قھوة‬

‫‪515‬‬

‫‪220‬‬

‫موقد عادي‬

‫‪930‬‬

‫‪525‬‬

‫‪290‬‬

‫توستر‬

‫‪1050‬‬

‫‪700‬‬

‫‪350‬‬

‫شواية فراخ‬

‫‪2190‬‬

‫‪2190‬‬

‫‪875‬‬

‫قدرة الموتور‬ ‫أقل من ‪ 200‬وات‬

‫الكفاءة‬ ‫‪0.60‬‬

‫من ‪ 375‬إلى ‪ 750‬وات‬

‫‪0.70‬‬

‫من ‪ 1‬إلى ‪ 4‬كيلو وات‬

‫‪0.80‬‬

‫من إلى ‪ 15‬كيلو وات‬

‫‪0.85‬‬

‫أكب رمن ‪ 15‬كيلو وات‬

‫‪0.88‬‬

‫‪29‬‬

‫‪• For equipment with electric motor.‬‬ ‫‪•
4 54 = 67 ∗ 8"0"$ 9"%$‬‬

‫)‪Cooling load calculation (Manually‬‬

‫حالة التواجد‬

‫خواص المكان‬ ‫مساحة األرضية لكل‬ ‫شخص )‪(m2‬‬

‫خاوي‬ ‫بنك ـ معمل‬

‫‪8‬‬

‫)‪• Ventilation load (sensible and latent‬‬ ‫‪.‬‬ ‫; ‪
:4, = 8‬‬ ‫ ‪∗ ℎ − ℎ‬‬ ‫‪.‬‬ ‫; ‪
:4,4 54 = 8‬‬ ‫‪∗ ℎ − ℎ‬‬ ‫‪.‬‬ ‫; ‪
:4,4 = 8‬‬ ‫ ‪∗ ℎ − ℎ‬‬ ‫التدخين‬

‫معدل التھوية‬ ‫)‪(L/S/m2‬‬

‫عدد مرات تغيير‬ ‫الھواء كل ساعة )‪(ξ‬‬

‫ممنوع‬

‫‪1‬‬

‫‪1‬‬

‫أحيانا ً‬

‫‪1.4‬‬

‫‪1.5‬‬

‫مطعم‬ ‫مكتب‬

‫دائما ً‬

‫‪1.8‬‬

‫‪2‬‬

‫مكتظ‬

‫ممنوع‬

‫‪2.8‬‬

‫‪3‬‬

‫أحيانا ً‬

‫‪3.7‬‬

‫‪4‬‬

‫دائما ً‬ ‫ممنوع‬

‫‪4.6‬‬ ‫‪6.7‬‬

‫‪5‬‬ ‫‪7‬‬

‫أحيانا ً‬

‫‪8.3‬‬

‫‪9‬‬

‫دائما ً‬

‫‪10‬‬

‫‪11‬‬

‫غرف عامة‬

‫‪4‬‬

‫فنادق‬ ‫مزدحم‬ ‫بار ـ صالة‬ ‫محالت تجارية‬ ‫اجتماعات ـ ‪30‬‬

‫‪2‬‬

‫‪• Air flow rate‬‬ ‫‪• Air change method‬‬ ‫‪• Floor area method‬‬ ‫‪• Person requirements method‬‬

‫)‪Cooling load calculation (Manually‬‬ ‫‪• Ventilation rate L/s/person‬‬ ‫االستخدام‬

‫‪31‬‬

‫التدخين‬

‫معدالت التھوية‬ ‫األدنى‬ ‫‪7‬‬

‫المفضل‬ ‫‪9.5‬‬ ‫‪7.5‬‬

‫شقة‬

‫أحيانا ً‬

‫بنك‬

‫أحيانا ً‬

‫‪5‬‬

‫صالون‬

‫أحيانا ً‬

‫‪5‬‬

‫‪7‬‬

‫بار‬

‫شديد‬

‫‪12‬‬

‫‪15‬‬

‫محالت تجارية‬

‫ممنوع‬

‫‪2.5‬‬

‫‪3.5‬‬

‫مصانع‬

‫ممنوع‬

‫‪3.5‬‬

‫‪5‬‬

‫مستشفيات‬

‫ممنوع‬

‫‪12‬‬

‫‪14‬‬

‫فنادق‬

‫شديد‬

‫‪12‬‬

‫‪14‬‬

‫غرف اجتماعات‬

‫شديد‬

‫‪14‬‬

‫‪24‬‬

‫مكاتب خصوصية‬

‫أحيانا ً‬

‫‪7‬‬

‫‪12‬‬

‫مكاتب عامة‬

‫أحيانا ً‬

‫‪7.5‬‬

‫‪12.5‬‬

‫مطاعم‬

‫أحيانا ً‬

‫‪7.5‬‬

‫‪10‬‬

‫كفتيريا‬

‫أحيانا ً‬

‫‪3.5‬‬

‫‪6‬‬

‫مسارح‬

‫ممنوع‬

‫‪2.5‬‬

‫‪5‬‬

‫)‪Cooling load calculation (Manually‬‬ ‫‪• Infiltration load‬‬

‫‪.‬‬ ‫; ‪
=, = 8‬‬ ‫ ‪∗ ℎ − ℎ‬‬ ‫‪.‬‬ ‫; ‪
=,4 54 = 8‬‬ ‫‪∗ ℎ − ℎ‬‬ ‫‪.‬‬ ‫; ‪
=,4 = 8‬‬ ‫ ‪∗ ℎ − ℎ‬‬ ‫)‪• Infiltration rate through cracks (L/s/m‬‬ ‫العنصر‬

‫سرعة الھواء )‪(m/s‬‬ ‫‪5‬‬ ‫‪2‬‬

‫شباك ذو إطار خشبي بمفصالت‪:‬‬ ‫جيد اإلحكام‬

‫‪0.19‬‬

‫‪10‬‬

‫ضعيف اإلحكام‬

‫‪0.70‬‬

‫‪2.87‬‬

‫‪0.16‬‬

‫‪0.82‬‬

‫‪5‬‬

‫‪15‬‬

‫شباك ذو إطار معدني بمفصالت أو منزلق‬ ‫باب زجاجي جيد التركيب‬ ‫باب خشبي أو معدني‪:‬‬ ‫‪32‬‬

‫جيد التركيب‬

‫‪1.4‬‬

‫‪2.8‬‬

‫ضعيف اإلحكام‬

‫‪1.4‬‬

‫‪5.7‬‬

‫)‪Cooling load calculation (Manually‬‬ ‫)‪• Infiltration rate based on application (ACH‬‬ ‫)‪(ξ‬‬ ‫نوعية المبنى والغرف‬

‫نوافذ عادية‬

‫نوافذ محكمة‬

‫صاالت الدخول‬

‫‪1.8 – 1.2‬‬

‫‪0.9 – 0.6‬‬

‫صاالت االستقبال‬

‫‪1.2‬‬

‫‪0.6‬‬

‫الحمامات‬

‫‪1.2‬‬

‫‪0.6‬‬

‫نافذة أو باب مع‪:‬‬ ‫حائط واحد‬

‫‪0.75‬‬

‫‪0.5‬‬

‫حائطين‬

‫‪1.5‬‬

‫‪0.75‬‬

‫ثالثة حوائط‬

‫‪2‬‬

‫‪1‬‬

‫أربعة حوائط‬

‫‪2‬‬

‫‪1‬‬

‫‪2‬‬

‫‪-‬‬

‫محالت تجارية‬

‫‪33‬‬

Air conditioning systems (HVAC (HVAC) AC) Air conditioning systems Package units

Roof top ducted

Vertical ducted

Split units

Decorative Ducted ductless Terminals

AHU

VRV

Decorative Ducted FCU ductless

Hydronic

AHU

Decorative Ductless

Air control = VAV or CAV 34

Air conditioning systems (HVAC (HVAC) AC) • Package unit, Roof top ducted • Cooling capacity (4–20 TR) • Applications • Banks • Small administrative buildings

35

Air conditioning systems (HVAC (HVAC) AC) • Package unit, Vertical ducted • Cooling capacity (4–20 TR) • Applications • Banks • Small administrative buildings

36

Air conditioning systems (HVAC (HVAC) AC) • Package unit, decorative ductless • Cooling capacity (Up to 2 TR) • Residential applications • Easy to install • Easy maintenance • Noisy

37

Air conditioning systems (HVAC (HVAC) AC) • Split unit, Decorative ductless • Cooling capacity (Up to 2 TR) • Residential applications • Easy to install • Easy maintenance

38

Air conditioning systems (HVAC (HVAC) AC) • Decorative ductless split and package units • Less expensive to operate than central units. • Their efficiency is generally lower than that of central air conditioners. • Does not need special electrical current specifications. • Its maintenance cost is very low compared by central or mini central. • Split units is more preferable than window units in term of noise and shape. • Capacities up to 2TR. 39

Air conditioning systems (HVAC (HVAC) AC) • Split unit, Ducted terminal (small capacity, mini central) • The outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator • Capacity of (1.5-5 TR) • Its common name is (ceiling concealed ducted CCD) • Applications • • • •

Banks Residential (villas) Small administrative building Retails 40

Air conditioning systems (HVAC (HVAC) AC) Return air could be free return or ducted return

41

Air conditioning systems (HVAC (HVAC) AC)

42

Air conditioning systems (HVAC (HVAC) AC) • Split unit, AHU • Used in special air requirement. • • • •

Clean rooms. Special industrial applications. Comfort applications of special requirement. Cooling capacity depends on the manufacturer.

43

Air conditioning systems (HVAC (HVAC) AC) • VRF system • Multi-split system turn on / off based on master controller. • VRF continually adjust the refrigerant flow to each indoor evaporator.

44

Air conditioning systems (HVAC (HVAC) AC) • VRF system • The modern VRF technology uses an inverter-driven scroll compressor and permits as many as 48 or more indoor units to operate from one outdoor unit. • The inverter scroll compressors are capable of changing the speed to follow the variations in the total cooling load as determined by the suction gas pressure measured on the condensing unit. 45

Air conditioning systems (HVAC (HVAC) AC)

46

Air conditioning systems (HVAC (HVAC) AC)

47

Air conditioning systems (HVAC (HVAC) AC) • Chilled water system

48

Air conditioning systems (HVAC (HVAC) AC) • Chilled water system, Ducted FCU • Chilled water system, AHU • Chilled water system, Decorative ductless.

Air cooled chiller

Water cooled chiller

49

Air conditioning systems (HVAC (HVAC) AC)

50

Variable air volume (VAV) system

51

Variable air volume (VAV) system

52

Variable air volume (VAV) system • A traditional VAV system consists of a VAV box with a damper to control the volume of air delivered to a space. When the space approaches design conditions, the damper may close to provide only 15% of the design cfm. 53

Variable air volume (VAV) system • Fan Powered VAV: The addition of a fan to a VAV box improves air movement at times when a space is near its design temperature and supply air volumes are low • Advantages: • High efficient and not very high initial cost. • Independent thermostat base space control. • High grade of flexibility.

• Disadvantages • VAV box needs space. • Inefficient in different space applications. 54

Notes • Air has to be conditioned in most cases for us to be comfortable. • Equipment includes cooling coil, heating device, device to add humidity, and device to clean air. • Air systems use the same room air over and over again. • Fresh air enters the structure by infiltration or by mechanical means. • Different spaces require different air quantities. • Same structure may have several different cooling requirements. 55

Air distribution

56

Air outlets

Perforated diffuser Jet diffuser

Round diffuser

2 way square diffuser

Round twist diffuser 3 way square diffuser

57

Air outlet selection

58

Air outlet distribution and distances

100 cfm

200 cfm

50 cfm

100 cfm

100 cfm

50 cfm

Living Room

100 cfm

200 cfm

300 cfm 59

Supply duct system • Distributes air to the terminal units, diffusers in the conditioned space • Duct systems • Plenum system • Extended plenum system • Reducing plenum system • Perimeter loop

60

Plenum system • Suited for a job where the room outlets are all close to the unit. Supply plenum Branch ducts

Return duct

61

Extended plenum (trunk duct) system • Can be applied to a

50 cfm 100 cfm

200

cfm

100 cfm 100 cfm

long structure. 50 cfm

• This system takes the plenum closer to the farthest point. • Low

noise

100 cfm

level

Living Room 9,000 btu (cooling) 18,000 btu (heating) 300 cfm

200 cfm

applications. 62

Reducing plenum system • Reduces the trunk duct size as branch ducts are added • Has the advantage of saving material and keeping the same pressure from one end of the duct system to the other

200 cfm

50 cfm

100 cfm

100 cfm

100 cfm

50 cfm

Living Room 9,000 btu (cooling) 18,000 btu (heating) 300 cfm 100 cfm

200 cfm

63

Perimeter loop system

100 cfm

200 cfm

50 cfm

Living Room 9,000 btu (cooling) 18,000 btu (heating) 300 cfm

100 cfm

100 cfm 50 cfm

100 cfm

200 cfm

64

Perimeter loop system • Well suited for installation in a concrete floor in a colder climate (heating applications). • Warm air is in the whole loop when the fan is running. • Keeps the slab at a more even temperature. • Provides the same pressure to all outlets. 65

Duct materials • Ductwork must meet local HVAC code. • Galvanized sheet metal was used exclusively. • Other ductwork materials.

Fiberglass duct-board

• Pre-insulated Aluminum duct. • Fiberglass duct-board. • Spiral metal duct. • Flexible duct. Spiral duct Pre-insulated Aluminium duct

Flexible duct 66

Galvanized steel duct assembly • Metal duct can be round, square, or rectangular

Slip Drive cleat J O I N I N G S E C T I O N S O F G A LV A N I Z E D D U C T WITH SLIPS AND DRIVES

67

Galvanized steel duct assembly

Ends of drives are bent over to secure J O I N I N G S E C T I O N S O F G A LV A N I Z E D D U C T WITH SLIPS AND DRIVES

Slip

68

Other duct types • Fiberglass duct-board. • Flat sheet or round prefabricated cut • Duct is normally 1’’ thick with aluminum foil backing • All duct seams should be stapled and taped

Fiberglass duct-board

• Spiral metal duct • Used more on large systems. • Comes in rolls of flat narrow metal. • Runs can be made at the job site. Spiral duct 69

Combination duct system • In HVAC duct work you may find the following combinations • Metal trunk lines with round branch ducts. • Metal trunk lines with flexible branch ducts. • Ductboard trunk lines with round metal branch ducts. • Ductboard trunk lines with flexible branch ducts. • Round metal duct with round metal branch ducts. • Round metal trunk lines with flexible branch ducts. 70

Duct air movement • Branch ducts are fastened to the main trunk by a takeoff-fitting. • The takeoff encourages the air to enter the branch duct. Main supply duct

Takeoff fitting

71

Balancing (volume) dampers • Used to balance the air in various parts of the system. • Dampers should be located as close as practical to the trunk line. • Handles allow the dampers to be turned at an angle to the airstream to slow the air down. Branch duct

Damper in the open position

Balancing damper in the closed position

72

Duct insulation • About 10°C temperature difference from the inside of the duct to the outside of the duct is considered the maximum difference allowed. • Metal duct can be insulated on the outside and on the inside. • The insulation is joined by lapping it, stapling it, and taping it.

Internal insulated duct

External insulated duct

73

Central Return duct

Supply plenum

Return plenum

One central return grill in the common area 74

Individual return duct

S R

75

Air duct design (consideration) • The following parameters are considered • • • •

Heat loss or gain through air duct. Maximum allowable aspect ratio. Air friction loss. Used fittings.

• Low velocity air duct system • Vair = 6 - 12 m/s • ΔP = 0.8 – 1.5 Pa/m

• High velocity air duct system • Vair = 12 - 30 m/s • ΔP = 3 – 5 Pa/m 76

Air duct design (steps) • Building drawings. • Select air duct system (plenum, extended plenum, reduced plenum, perimeter). • Select air outlet positions (supply and return). • Select air outlets types based on air volume and distribution. • Duct routing (the simplest and shortest). • Find duct dimensions. • Find the total pressure drop to select the proper fan section. 77

Friction chart for round duct

78

Convert from round duct to rectangular duct

79

Using ductduct-sizer software

Modify your dimensions

Step-1

Step-2

Step-3

Step-4 80

Air fans • Provides the pressure difference to moves the air through the duct system, dampers and outlets with a proper velocity. • Typically 400 CFMair/TR for DX coils and 350 CFMair/TR for chilled water coils. • Duct system pressures. • Static pressure. • Velocity pressure. • Total pressure = static pressure + Velocity pressure. 81

Air fans Air fans Propeller

Centrifugal

fans

fans

82

Air fans Air fans Propeller

Centrifugal

fans

fans

• Used in exhaust air system. • Will handle large volumes of air at low pressure differentials. • Makes noise and is used where noise is not a factor.

• Desirable for ductwork. • Builds more pressure from the inlet to the outlet. • Very quiet when properly applied. • Can be used in very large highpressure systems. 83

Air fans

DIRECT DRIVE MOTOR ASSEMBLY

84

Air fans BLOWER

MOTOR

BOTH THE DRIVE AND DRIVEN PULLEYS MUST BE PERFECTLY ALIGNED

BeltBelt-driven Assembly

85

86