HVAC Comfort
environment for people (Human beings) Engineering Services
Building Construction Industry
Industrial Plants
Residential
Process
(Homes, Villas, Apartments etc)
Chilled Water Hot Water
Staff Building Administrative Building, Staff Accommodation, Canteen, Hospital etc
Designer realize
Comfort & Safety of Occupants
HVAC design & drafting
Client
Consultant
Contractor
Owner
Designer
Installer
Getting Project from Client Main Consultants
Sub Consultant
Civil Engineering
MEP
Execution of jobs
Main Contractor
Sub Contractor
Civil Engineering
MEP (Electro Mechanical)
1
HVAC Design
1. Consultants
Designing (Design Consultant) Site Supervisors (Project Consultant) Testing / Inspection Approvals Commissioning
2. Contractor
Supervision of Installation (Project Engineer / Site Engineer) Project Estimation (”) Project Approvals (”) Procurement Procurement (Purchase)
3. Maintenance
Drafting
Drawings to convey the design HVAC Software’s
Load Calculations Block Load, HAP, CHVAC, RHVAC Carrier
Elite
2
H
Heating
V
Ventilation
A/c Air Conditioning
WINTER (Cool)
Hot Air
SUMMER (Hot)
Temperature
Fresh Air
I ndo ndoor
Cool Air Humidity Level Maintaining
Heating
It is the process of adding heat to the space by using hot air to maintain the comfort conditions in the space. Ventilation
It is the process of maintaining indoor air qualities qualities either by removing used air or by adding fresh air. Air Conditioning
It is the process of adjusting the temperature, humidity humidity levels & purifying the air to satisfy human comfort comfort conditions.
T he com comfor t cond condii tio tions are ar e:
25˚C or 76˚F Temperature 30 – 30 – 70% 70% RH (Ideally 50% RH) RH
Relative Humidity
RH = Amount of moisture in Sample Air Saturated Air Saturated Air
Air with 100% Moisture Content
3
HVAC Standards
ASHRAE
American Society of Heating Refrigeration & Air Conditioning Engineering
ISHRAE
Indian Society of Heating Refrigeration & Air Conditioning Engineering
Ducting Standards
SMACNA
Sheet Metal Air Conditioning Contractors National Association
DW 142
Duct Work 142
Piping Standards
ASME B 31.3 ASME B 31.9 ASME B 31.5 ASTM ARI UBC UMC
Process Piping Building Services Piping Refrigerant Piping American Society for Testing & Materials American Refrigeration Institute Uniform Building Code Uniform Mechanical Code (Equipment Installation)
Concepts of HVAC
Introduction of HVAC & A/c Equipments Air Distribution System Kitchen Ventilation System Chilled Water System Chilled Water Pipe Designing Equipment Selection
4
Refrigerant
It is a gas / liquid which boils / evaporates at very low temperatures. E.g. Lithium Bromide Ammonia
– BP - 5˚C – BP - 10˚C
Refrigerants can be kept under pressure to maintain the liquid state. E.g. LPG – Liquefied Petroleum Gas List of Refrigerants
Refer Page D-2 = HVAC Handbook Principle of Air Conditioning
Vapour Compression System / Vapour Compression Cycle Absorption Chilling System
Vapour Compression Cycle (VCC)
Condenser
Refrigeration pipe (Cu)
Expansion Valve
Evaporator
Compressor
(Refer Page D-3 = HVAC Handbook)
5
Evaporator
It is an array of tube / Heat Exchanger where refrigerant absorbs heat & evaporates.
Fins (Increases the surface area of contact) Supply Header (Coil/Tube) Return Rows of Coils
Condenser
It is an array of tube / Heat Exchanger where refrigerant rejects heat & condenses in to liquid. Expansion Valve
It is an Orifice / a Capillary tube used to release the pressure of refrigerant. It also regulates the flow of refrigerant (so valve). Orifice
Compressors
It is used to increase the pressure of refrigerant gas. It handles only gas. It is the driver of the complete cycle.
6
Working of VCC
Gas Ref:
Liquid Ref:
Expansion
Evaporates
Pressure Temperature
Outside air
hot air to atmosphere
Ref: liquid Moderate Temp-HP
Ref: gas HP-HT Fan
Ref: liquid LP-LT
Ref: gas HT-LP
Cool air space
Note:
Copper tubes / coils are used because of high heat transfer rate. From Condenser to Evaporator
Liquid line
From Evaporator to Compressor
Suction line
From compressor to Condenser
Hot gas line / Discharge line
7
Super Heat mode of Refrigerant
It is the heat added to the refrigerant on the suction side / line of the compressor (due to high outside temperature). Sub Cooling
It is the heat rejected from the discharge line to the atmosphere (due to low atmospheric temperature) Absorption Chilling System NH3 vapour
NH3 liquid
Condenser
Expansion Valve Chilled water in
Out
NH3 gas
Span
Absorber
H2o+NH3
No
electricity Fossil fuels are using. Less efficient, because no control on pressure.
Absorption Chilling System is less efficient than VCC. All the Air Conditioners now have VCC.
8
Classification of Air Conditioning Systems Local cooling comfort system (M/c inside the space)
Window A/c Split A/c Multi Split A/c Chilled Water Fan Coil Unit
Centralized A/c System (M/c outside the space)
Central A/c System / All Air System Chilled Water System / Air Water System
Window A/c
It pulls room air & blows it over the Evaporator for conditioning of air. Outside
Window
Inside Space
Partition Compartment
It is installed in the window; the condenser side should be outside the window. It is available up to 3TR capacity. (TR Tonne of Refrigeration) It is used for single room small applications.
9
Split A/c
Insulation
Outdoor / Condensing Unit
Indoor Unit
It pulls room air & blow over the Evaporator for Air Conditioning of room air. Available capacity up to 7-8TR Length of refrigerant pipe can be taken from catalog. Generally, length should not exceed 40-50m. Outdoor unit can be mounted on the roof & also on the wall.
Advantages Not
much space required / No breaking of window. Noise is removed from the space. No chance of mixing of air. Indoor unit types
Ducted type Non-Ducted type Outdoor unit types
Vertical discharge unit Horizontal discharge unit
10
Multi Split A/c
Ref: Pipe IU - 1
IU - 2
IU - 3
IU - 4 Branch Distributor Outdoor Unit
Multiple Indoor units are connected to a single Outdoor unit. The Indoor unit capacities are based on space requirement. The Outdoor unit capacities are based on Indoor units. Branch Distributor helps to distribute the amount of refrigerant required. Check the limitations of pipe lengths during installation. Different Branch Distributors are available which are selected based on the unit selections.
VRF System: Various Refrigerant Flows (DAIKIN)-Ref net VRV System: Various Refrigerant Volumes (LG)-Branch Distributor
11
Chilled Water Fan Coil Unit
Chilled Water Inlet
Coil (Heat Exchanger)
Chilled Water Outlet
Capacity up to 7.5TR
FCU type (Fan Coil Unit)
Ducted Non-Ducted
12
CENTRALISED A/c SYSTEM Chilled Water System
Chiller/ Cooler
FCU
AHU
Supply Chilled Water Pipe P1
P2
Return
FCU
Fan Coil Unit
AHU
Air Handling Unit
13
Central A/c System
AHU
AHU is the heart of Central A/c System, which works on VCC. It can be installed on the Roof / Basement / Mechanical Rooms.
DX Units
Chilled Water Units
Window A/c
FCU
Split A/c Multi Split A/c
Local
AHU
AHU
Package Unit Chiller DX
Central Direct Expansion
14
Functions of Air Handling Unit
Cooling Heating Humidification Dehumidification Filtration
Cooling
Refers to removal of heat from air. For removing heat we use Cooling Coils / Heat Exchanger.
Heat Exchanger
Component involved in exchange of heat.
Types of Cooling Coil
DX coil Chilled Water coil
DX coil
Used in VCC (Refrigerant flowing through it)
Chilled Water coil
Used in Chilled Water Cycle (Chilled Water flowing through it)
Selection of Coil
Based on:
More no’s of R ows Less Coil face air velocity (400 – 700 fpm) fpm
feet per minute
15
Heating
Refers to the addition of heat to the air.
Heating Coil
Heat Exchanger
Types of Heating Coil
Hot Water Coil Steam Coil Electric Heating Element
Hot Water Coil
Hot water flowing through it. Boiler produces hot water & it circulated through radiators & AHU’s to give the heat in the space. Hot water is flowing in Hot Water Coils, used in radiators & AHU’s.
Steam Coil
Steam Boiler produces steam, which is supplied to Steam Coils installed in AHU’s & radiators.
Electric Heating Element It
can be mounted in AHU / in the ducts which gets heated up by using electricity. Used for small capacities.
16
Humidification
Adding moisture to the air during Winter season. Humidification is done with heating.
Winter season
Temperature RH 90%
5 - 10˚C
When heating is done:
Temperature RH (RH
50 – 40%)
Methods of Humidification Wet Humidification Steam Humidification
17
Wet Humidification
Mixing Box
Heating Coil Reheat Coil Fan
F.A
S.A
Schematic of AH U
R.A Spray Nozzle
R.A
Return Air
F.A
Fresh Air
S.A
Supply Air
Using water for Humidification. Air is heated up by using a Heating Coil. Spray Nozzles sprinkle water molecules on the hot air stream. Water vaporizes, thus humidifying the air. In this process temperature of air drops; so a Reheat Coil is used to increase the temperature.
18
Steam Humidification
Mixing Box
Heating Coil
F.A
S.A
R.A Steam Humidifier
Using Steam for Humidification. Air is heated up by using Heating Coil. Steam is added to the air, thus humidifying the air. Humidified air is supplied to the space.
19
Dehumidification
Removal of moisture from air during summer season.
Summer season
Temperature 45 - 50˚C RH 20 – 25%
When cooling the air:
Temperature RH
(RH
up to 50%)
Methods of Dehumidification
DPT method (Dew Point Temperature) Chemical Dehumidification
DPT method (Dew Point Temperature)
It is the maximum temperature of air below which moisture starts condensing in to liquid. The temperature of Cooling Coil is set below the Dew Point Temperature of air. Thus the moisture is removed by dehumidifying the air.
Chemical Dehumidification
Silica Gel is used for dehumidification. It has a property of absorbing moisture from the air. Disk is applied with Silica Gel & air is made to pass over it. Maintenance of disk is to be done periodically.
20
Filtration It is to purify the air from foreign particles / contaminants like bacteria, dust, odour etc. present in the air Types of Filtration
Mechanical Filtration Electrostatic Filtration
Mechanical Filtration Types of Filters
Pad Filters Panel Filters Anti-microbial Filters Bag Filters HEPA Filters (High Efficiency Particulate Air Filters) ULPA Filters (Ultra Low Particulate Air Filters)
21
Pad Filters
Frame (Al) Filter Media
It is the first bank of filters The Filter Media is a porous material (cloth / fibre), which is held in a Frame work. It stops large dust particles.
22
Panel Filters
Frame Work Filter Media
The Filter Media is folded in pleats. The dust collection capacity is higher than Pad Filters.
Anti-microbial Filters
These are Pad / Panel Filtered sprayed with Biocides to kill the bacteria Used mostly in Hospitals, Malls, Labs, Offices etc.
23
Bag Filters
Filter Media Frame Work
The Filter Media is folded in to Bags to increase the dust collection capacity.
24
HEPA Filters (High Efficiency Particulate Air Filters)
These are basically Panel / Bag Filters with specialized Filter Media which gives 99% clean air. Application
Hospitals (Operation Theatres, ICU’s Labs etc.) Food Processing Units etc.
ULPA Filters (Ultra Low Particulate Air Filters)
These are basically Panel / Bag Filters with specialized Filter Media which gives 99.99% clean air. Application
Defense Nuclear Industries Space (Space Stations) etc.
25
Electrostatic Filtration
Primary Filter
Air
-ve
Secondary Filter
+ve
Negatively charged Ionizer Positively charged dust collecting plates
Primary Filters removes large dust particles & the remaining particles are negatively charged through Ionizer which is attracted to positively charged dust collecting plates. Any remaining dust particles are captured in Secondary Filters. Maintenance is required for dust collecting plates.
26
Package Unit / DX Package Unit / Package A/c Unit (PACU)
Condenser Fan
Compressor
Condenser
S.A
Evaporator
Return Air
Expansion Valve
It is a bigger version of Window A/c. The Evaporator, Condenser, Compressor, Expansion Valve & the Blowers are in one cabinet, which cannot be modified. It can be installed on Roof Top / Basement / Mechanical Rooms with duct connecting to it. Available capacity up to 30TR
27
Split type AHU
Condenser
Compressor
ACCU
Evaporating Unit /
(Air Cooled Condensing Unit)
Evaporator
Indoor AHU
The AHU is splitted in Evaporating Unit & ACCU. ACCU is installed outside. Evaporating Unit is installed inside. Capacity up to 20TR
28
Properties of Air
The Thermodynamic properties of air are:
Dry Bulb Temperature (DBT) Wet Bulb Temperature (WBT) Relative Humidity (RH) Humidity Ratio (HR) Dew Point Temperature (DPT) Enthalpy
Dry Bulb Temperature (DBT)
It is the temperature measured with ordinary thermometer. Wet Bulb Temperature (WBT)
It is the temperature measured with ordinary thermometer covering a wet cloth over the bulb. Relative Humidity (RH)
It is the amount of moisture in sample air to the ratio of saturated air. RH = Amount of moisture in Sample Air Saturated Air Humidity Ratio (HR)
It is the ratio of grains of moisture present per pound of air. HR = Grains of moisture Pounds of Air
29
( Gr/lb)
Dew Point Temperature (DPT)
It is the maximum temperature of air below which moisture starts condensing in to liquid.
Enthalpy
It is the total heat content in the air.
Note:
Psychometric Chart is used to find the Thermodynamic properties of air. Any two values to be known to find the rest.
30
Air Distribution System This system is design to distribute the air in the building from AHU, by using duct.
Duct
It is a conduit, used to convey air either from machine to the space or space to the machine.
Duct Material
Galvanized Iron / Steel Sheet Fibre Glass Flexible Aluminium Semi Rigid Fabric Flexible
Rigid & Heavier
Duct Shapes
Rectangular Duct Circular / Round Duct Oval Duct
Note:
Main duct should always be Rectangular. Branch duct can be Rectangular / Circular.
31
Duct in Sectional & Plan View Supply Air Duct
S.A
Sectional View
Plan View
Return Air Duct
R.A
Sectional View
Plan View
Fresh Air Duct
F.A
Sectional View
Plan View
Exhaust Air Duct
E.A
Sectional View
Plan View
32
Duct Riser & Drop Plan / Top View Supply Air Duct
Riser
Drop
Return Air Duct
Fresh Air Duct
Exhaust Air Duct
33
Duct Offset
Duct Offset
Used to change the Elevation / position.
Change in Elevation
Beam
Slab
Sectional View
DN
UP
Top View
34
Change in Position
Wall
Top View
Types of Ducts Supply Air Duct
Handling conditioned air from machine to space.
Return Air Duct
Handling return air from space to machine.
Fresh Air Duct
Handling fresh air from atmosphere to machine.
Exhaust Air Duct
Handling exhaust air from space to atmosphere.
35
Components of Air Distribution System
End Cap
Elbow Wall Tie Damper
Flexible Duct
Reducer Branch Take off
Diffuser
Diffuser Plenum Sound Attenuator
Damper Flexible Connector
Duct Liner
Starting Collar Plenum AHU
36
Plenum
It is the first attachment to the machine to which ducts are connected. Starting Collar
It is used if the Main Duct size & Plenum size are different. Flexible Connector
It is made up of fabric & used to remove the vibrations from the duct system. Fabric Metal Strips
Bolted
Duct Liner
Fibre glass material is lined inside the duct for acoustical insulation. It should be lined up to 20ft from the machine.
Sound Attenuator
It is used for acoustical insulation. It is basically installed in the main duct only. It is made up of GI material.
37
Sound Attenuator Selection
The selection is done based on:
Air volume it is handling (cfm) Noise levels to be maintained (db level / noise criteria) Duct routings
Documents to be given:
Drawings Roof drawing Floor drawing Machine catalogues Noise level specifications Note:
Check the physical dimension of Sound Attenuator & order the connection pieces, if required. Duct Wrap / Duct Insulation
Fibre glass insulation is wrapped over the duct for thermal insulations. Note:
For internal ducts, Insulation thickness = 0.5” – 2” For external ducts, Insulation thickness = 2” – 4” Internal insulation comes in rolls (flexible). External insulation comes in rigid boards (semi-rigid)
38
Flexible Duct
It is used to connect Branch Duct with Diffuser. It is flexible in nature, as it is made up of fibre glass material. These are basically circular in shape. Available up to 12” The length of Flexible Duct should be limited to 10ft. Flexible Duct size is based on the cfm it is handling.
Dampers
It is used to control the flow of air. These are used for air balancing.
Types of Dampers
Volume Dampers Fire Dampers Splitter Dampers Relief Dampers
Volume Dampers
These are installed in every branch & in the main duct to regulate the volume of air to be flown. Types
Butterfly Damper Multi-blade Damper
39
Butterfly Damper
Motorized Actuator
Duct Disc
T
Thermostat
It uses disc to regulate the flow of air. Disc parallel to air flow gives 100% flow. Disc perpendicular to air flow gives no flow. In a manual damper, the plates have to be set as per the flow required.
40
Multi-blade Damper
It is installed in the main ducts.
Blades
Types
Parallel Blade Opposed Blade
41
Parallel Blade
Rotating parallel & in direction of air flow.
Opposed Blade
Rotating against each other.
Note:
Movement of blade is controlled by Actuators.
42
Fire Dampers
Fire Damper AHU
These are installed with the ducts which are passing through slab / walls. It is used to stop the flow of air during the event of fire. It has fusible link which melts & break during the event of fire.
Fusible Link Shutter
Motorized Fire Dampers are also available, which is interfaced with fire detectors.
Note:
All the dampers are made up of GI material. It must be used in every duct.
43
Splitter Dampers
Splitter Damper
It is used for splitting of air in the branches.
Relief Dampers
It is used to release the excess air pressure build up in the ducts.
Branch Take-off
It is a fitting used to create branch connection either from rectangular duct to rectangular duct or from rectangular duct to round duct.
Takeo-ff position
Top Take-off Side Take-off
44
Branch Types
Y-Branch
Double - Y
45
Access Doors
Access Doors are used to have access to the components which requires repair & maintenance Access Doors should be made in the fall ceiling & also in the ducts.
Diffusers
These are air outlets connected with the ducts to give air in the space & also to take air from the space. Types of Installation
Diffuser installed in fall ceiling
Grill installed in step of fall ceiling
Grill installed in fall wall
46
Diffuser installed in fall floor
Grill installed in the wall
(No fall ceiling)
Types of Air Outlets Square Diffuser
4-Way
3-Way
2-Way
1-Way
47
Round Diffuser
Perforated Diffuser
Linear Slotted Diffuser
Stair Case Diffuser
4-Slot / 3-Slot / 2-Slot
Swirl Diffuser
Grill
Linear Bar Grill
Register
48
Dimensioning Square Diffuser
W×L
Round Diffuser
Diameter (D)
Perforated Diffuser
W×L
Swirl Diffuser
Diameter (D)
Stair Case Diffuser
W×L
Linear Square Diffuser
L×H
Grill
W×H
Linear Bar Grill
L×H
Register
W×H
Note:
The collar connecting diffuser & duct should be ordered as per the neck size.
Duct
Neck
Collar
Face
49
Standard Duct Fittings Standard Elbow
Long way Elbow Short Radius Elbow Short Radius Elbow No Throat Long Radius Elbow
Long way Elbow
R t = ¾ D R t
R h = D + ¾ D
R R h
R
Centre Line Radius
R h
Heel Radius
R t
Throat Radius
Note:
For rectangular ducts, replace ‘D’ with ‘W’ (Width of outlet). It gives pressure drop.
Short Radius Elbow
R t = 150mm (or) 6” R t
R h = 150mm + D
R
R=D
R h
50
Short Radius Elbow No Throat
D
Used when no space. It gives high pressure drop.
Long Radius Elbow
R t = D R t
R h = 2D
R
R = 1.5 D
R h
Long Radius Elbows are most preferred elbows. When there is no space, a Short Radius Elbow can be used. Short Radius Elbow offers high pressure drop. They (SREL) should be installed with the Turning Vanes. Turning Vanes are made up of GI material. It is a thin plate / sheet standing in the elbow.
51
Reducer
Used to connect bigger size of duct to a smaller size. Used to have reduction in duct size.
Types
Concentric Reducer Eccentric Reducer
Concentric Reducer
ᶿ
ᶿmax = 45˚ (Diverging) = 60˚ (Converging)
L
Slope of Reducer Maximum Length Minimum Length
L = 1: 7 = 1500mm = 150mm
Eccentric Reducer
L
Slope of Reducer Maximum Length Minimum Length
= 1: 7 = 1500mm = 150mm
52
Length of Reducer
Example
200mm 800mm
ᶿ
1000mm 200mm L=?
tanᶿ = 1/7 = (opposite side ÷ adjacent side) = (100/ L) L = 7 × 100 = 700mm
53
Duct Routing Guidelines
Always route the duct straight & avoid more turnings.
Original duct size should be maintained, unless a reduction of 2” is required.
Provide Turning Vanes in the Short Radius Elbow.
Turning Vanes / Guide Vanes
Single Turning Vane should be provided for a Turning Width (R h) of 12” or less in an elbow.
Two Turning Vanes for Turning Width of 24” or less.
Three Turning Vanes for Turning Width of more than 24”.
Provide Volume Dampers for every branch, for balancing of air.
Provide Fire Dampers in the duct, passing through slab/wall/roof.
Provide Splitter Dampers near the Branch Take-offs, more than one in a same place.
Maintain minimum clearance of 6” from the fall ceiling / slab / any obstructions.
54
Duct Routings Spine
AHU
L - Shape
AHU
H - Shape
AHU
55
Perimeter
AHU
Trunk & Branch
AHU
56
Supply Duct Configurations Extended Plenum System / Trunk & Branch System
Plenum
Main Duct / Trunk Duct
AHU
Branch Duct
Used for Single & Multistoried application. Maximum space of main duct = 100 ft
Radial System / Spider System
Branch Plenum of AHU
Used for single storied application only. No main duct used. Branches originate directly from Plenum.
57
Return Duct Configurations Individual Return / Room-by-Room Return (A)
Shaft
Return Duct connected to each Return Diffuser in each space & routed to machine.
(B)
Duct left in each space above fall ceiling, but not connected to Diffuser & routed to machine.
58
Central Return System
Main Return Duct is left open in a central area above fall ceiling. All the air moves out of space from Return air opening & goes in the Return Duct.
Note:
For (B) & Central Return System, there should be no: of opening left unsealed in every space.
59
Duct Classification as per Velocity of Air
Low Velocity System Medium Velocity System High Velocity System fpm
(400 – 2000 fpm) (2000 – 2500 fpm) (2500 – 3000 fpm)
feet per minute (velocity)
Duct & Fan Classification as per Pressure
Class-I Class-II Class-II Wg
Low Pressure Medium Pressure High Pressure
up to 4” of wg 4” – 6” of wg 6” – 12” of wg
Water Gauge
AHU Classification
Roof Top Units (Double Skin) Indoor Type Units (Single Skin) Horizontal & Vertical AHU
Horizontal AHU
R.A
S.A
60
Vertical AHU
S.A
R.A
(or) S.A
R.A
61
Fan Arrangement in AHU
Blow Thru Draw Thru
Blow Thru
Draw Thru
62
Note:
In commercial A/c, Low Velocity & Medium Velocity System is used.
Main duct should be sized using Low / Medium Velocities.
Branch duct should be sized using Low Velocity System.
For industrial A/c High Velocity is used.
Most commonly used Fan Arrangement is Draw Thru.
For small capacity units like Window A/c & Split A/c, Blow Thru Fan Arrangement is used.
Backward Curve Centrifugal Fan should be used up to 30,000 cfm.
Above 30,000 cfm used Backward Inclined Blades Centrifugal Fan.
63
Minimum Fitting Spaces
AHU Minimum 2D distance AHU to first Elbow D
Duct Diameter (inches)
Minimum 6D distance between Elbow to Elbow
Minimum 6D
64
Thermal Zoning Zone
It can be a single space / multiple spaces served by common Air Handler & the control is done by one Thermostat. Two spaces are set to be in one zone if they have similar A/c requirements.
Dining Area Kitchen
3/5 Zones
2 Zones
Server Room
Air Delivery System
Single Zone System VAV System (Variable Air Volume) CAV System (Constant Air Volume)
Single Zone System
In this system one AHU is required to serve one space. The air flow & temperature control is done in the AHU itself.
AHU
T
65
VAV System
In this system Variable Air Volume terminals are used to vary the volume of air supplied to the space.
AHU
T
Control Unit
Inlet
T
T
Bypass Section
Outlet
CU
Damper
Power points should be specified according to the location of VAV for power supply. Control wiring should be done from Thermostat to VAV. VAV’s are available in different models based on the cfm it is handling. The connection pieces (inlet/outlet) have to be ordered during installation. VAV’s are made up of GI material.
66
CAV System
It is required two duct systems. In this system, volume of air is constant, but the temperature of air is varying.
Cooling Mode
Cool Air Duct
Hot Air Duct Temperature = 25˚C cfm = 2000
Damper
Heating Mode
Temperature = 40˚C
CA HA
cfm = 2000
Intermediate Mode
Temperature = 30˚C CA
HA
cfm = 2000
Note:
Single Zone System & VAV System are widely used. CAV System is used in Hospitals, Factories etc.
67
Heat Gain Calculations / Load Calculations / Cooling Load Calculations Cooling
Removal of heat from the space. Heat
It is a form of energy.
Heat can neither be created nor be destroyed. But can transfer from hotter region to cooler region. Units KJ, Kcal, BTU
KJ
Kilo Joule
Kcal
Kilo Calorie
BTU
British Thermal Unit
It is the amount of heat required to raise / lower 1˚F of temperature for 1lb of ice/water.
12,000 BTU/hr = 1 TR
TR
1 MBH = 1000 BTU/hr
MBH
12 MBH = 1 TR
68
Tonne of Refrigeration Mega British Hour
Temperature
It gives the intensity of heat. Units
˚C, ˚F, K
Heat Sensible Heat
Latent Heat
Latent Heat of Fusion
Latent Heat of Vaporization
Sensible Heat
It can be sensed by touch. It raises DBT.
Latent Heat
It cannot be sensed by touch, but associated with moisture. It raises WBT.
Latent Heat of Fusion
Amount of heat required to change the phase from solid to liquid at constant temperature. E.g. Ice (solid) 0˚C Water (liquid) Latent Heat of Vaporization
Amount of heat required to change the phase from liquid to gas / vapour at constant temperature.
69
Sources of heat gain in a Building envelop
Heat Gain through Glass/Window. Heat Gain through Wall & Roof. Heat Gain through Partition. Heat Gain from People. Heat Gain from Electrical Equipments. Heat Gain from Motors. Heat Gain from Kitchen Appliances. Heat Gain from Ducts. Heat Gain from Infiltration Air. Heat Gain through Ventilation Air. Heat Gain through By-pass Air. Heat Gain through Chilled Water Pumps.
Data required to start Heat Gain Calculation
Civil Plan (architect) Window, Wall & Roof details/ u-factors of wall, roof, floor & glass. (architect) Outdoor & Indoor design conditions. (specification) Daily Range, Wind Velocity (specification) Occupancy rate (architect) Lighting load (electrical engineer) Electrical Appliances (electrical engineer) Kitchen Appliances (specification) Any special requirement like Server room, Battery room. (Check with manufacturer)
70
Outdoor Design Conditions & its Corrections E xample: Washington City
DBT WBT
HR (Gr/lb)
Daily Range
Outdoor Conditions Refer Page A-11of HVAC Hand Book Daily Range
Difference of maximum & minimum temperature (DBT) on the hottest day of the year. Note:
Correction to Outdoor Condition is to be done to find the Temperature at specific month. Outdoor Temperature in April
Yearly Range Specific Month
Yearly Range
Difference in Summer Temperature & Winter Temperature. = 95˚F - 0˚F = 95˚F Correction to be done for April = -19˚F Refer Page A-13, Table-3 of HVAC Hand Book DBT in April
= 95˚F - 19˚F = 76˚F
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DBT in April at 10am For this we require: Daily Range Time Refer Page A-13, Table-2 of HVAC Hand Book Correction to be done for April at 10am = -10˚F DBT in April at 10am = 76˚F - 10˚F = 66˚F Indoor Conditions
Refer Page A-14 of HVAC Hand Book Comfort Conditions
76˚F DBT 56% RH
DBT(summer) = 74˚F - 76˚F RH = 50 % - 45% U-factor / Conductivity Factor U-factor can be calculated, based on the compositions.
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Wall composition
Brick (inches)
R o
R i
Cement Plaster ΣR = R o+ R i + R 1X1 + R 2X2 + ………. + R nXn Where, R o
Outside Air Film Resistance
R i
Inside Air Film Resistance
R 1, R 2, ……, R n
Resistance of materials
X1, X2, ……, Xn
Thickness of Materials (inches)
For R1 , R2 , ……, Rn & X 1 , X 2 , ……, X n U=
BTU/hr/˚F/sft
Refer Page A-25 & A-29 of HVAC Hand Book
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Roof Composition
Cement Plaster Fibre Glass Insulation Concrete (inches)
ΣR = R o+ R i + R 1X1 + R 2X2 + ………. + R nXn Where, R o
Outside Air Film Resistance
R i
Inside Air Film Resistance
R 1, R 2, ……, R n
Resistance of materials
X1, X2, ……, Xn
Thickness of Materials (inches)
For R1 , R2 , ……, Rn & X 1 , X 2 , ……, X n U=
BTU/hr/˚F/sft
Refer Page A-25 & A-30 of HVAC Hand Book
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Heat Gain through Glass / Window
Q = U×A× Sun gain Where, Q
Total Heat Gain in BTU/hr
U
Conduction Factor
A
Area of glass in sft
Sun gain
Heat Experienced by Glass(Temperature rise due to Heat) Maximum from 8.00am – 4.00pm
Refer Page A-18 of HVAC Hand Book
Note:
Location India Middle East USA
Hottest Month May August July
Latitude 20˚N 30˚N 40˚N
Daily Range 18˚F 28˚F 17˚F
Refer Page A-19, 20, 21 & 22 of HVAC Hand Book
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Heat Gain through Wall & Roof
Q = U ×A ×ETDcorrected Where, Q
Total Heat Gain in BTU/hr
U
Conductance Factor
A
Area of Wall/Roof in sft
ETDcorrected= ETDwall/roof + Correction (according to region) ETD
Equivalent Temperature Difference
Refer Page A-29, 23 & 24 Weight of Wall (lb/sft) 20 60 100 140
Thickness of Wall (inches) 4” 6” 8” 12”
Weight of Roof (lb/sft) 10 20 40 60 80
Thickness of Roof (inches) 2” 4” 6” 8” 10”
Correction:
Refer Page A-15 & A-24 with Temp: Diff: & Daily Range
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Heat Gain through Partition Partition
It is a glass, wall, floor/slab in partition with a non-A/c space. Wall partition
A/c
Non A/c
Exposed wall & glass
Q = U×A×ΔT Where, Q
Total Heat Gain in BTU/hr
U
Conductance Factor
A
Area of glass/wall/slab in sft ΔT = (T1 – T2)
T1
Outdoor Temperature
T2
Indoor Temperature
Note:
For Normal Partition (corridor, bathroom etc.), T1 = (T1 – 5) For Heat generating Partition (kitchen, laundry room etc.) T1 = (T1+15)
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Heat Gain from People
Sensible Heat Gain
= No’s of people × Sensible Heat/person
Latent Heat Gain
= No’s of people × Latent Heat/person
Q = Sensible Heat Gain + Latent Heat Gain Sensible Heat Gain/person & Latent Heat Gain/person is given by standards as per Type of application & degree of activity. Refer Page A-60 & A-36 of HVAC Hand Book
Heat Gain from Lights
Incandescent Lights Q = 3.41 × Watts Fluorescent Lights Q = 3.41 × Watts × 1.25 Note:
If wattage not known, wattage can be calculated by using: Watts = Areas × Watts/sft Refer Page A-60 of HVAC Hand Book
Heat Gain from Electrical Equipments
Q = 3.41 × Watts
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