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Training Session on Refrigeration & Air Conditioning
Refrigeration & Air Conditioning Presentation by
“Mohammad Salim” M/s Unitech Ltd., Gurgaon. 1
Training Agenda: Refrigeration & Air Conditioning Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
2
Introduction How does it work?
High Temperature Reservoir Heat Rejected R
Work Input
Heat Absorbed Low Temperature Reservoir 3
Introduction How does it work? Thermal energy moves from left to right through five loops of heat transfer: 1)
2)
3)
4)
5)
Indoor air loop
Chilled water loop
Refrigerant loop
Condenser water loop
Cooling water loop
(Bureau of Energy Efficiency, 2004)
4
Introduction AC Systems AC options / combinations: • Air Conditioning (for comfort / machine) • Split air conditioners • VRV System in Group Housing etc. • Fan coil units in a larger system • Air handling units in a larger system • Evaporating Cooling in a larger system
5
Introduction Refrigeration systems for industrial processes • Small capacity modular units of direct expansion type (50 Tons of Refrigeration) • Centralized chilled water plants with chilled water as a secondary coolant
(50 –
250 TR)
• Brine plants with brines as lower temperature, secondary coolant (>250 TR) 6
Introduction Refrigeration at large companies • Bank of units off-site with common • Chilled water pumps • Condenser water pumps • Cooling towers
• More levels of refrigeration/AC, e.g. • Comfort air conditioning (20-25 oC) • Chilled water system (8 – 10 oC) • Brine system (< 0 oC)
7
Reference Handbooks/Standards Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
8
Reference Handbooks/Standards ASHRAE Handbook of Fundamentals ASHRAE Handbook of Refrigeration ASHRAE Handbook of Application ASHRAE Handbook of System & Equipments ASHRAE Standards 62.1 ASHRAE Standards 90.1 ISHRAE Weather Data Carrier Handbook NBC-2005 LEED-2009 NFPA-92A ECBC-2007 Heat and Mass Transfer SMACNA Standard Indian Standards
9
Types of Refrigeration Introduction Reference Handbooks/Standards Types of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
10
Types of Refrigeration Refrigeration systems • Vapour Compression Refrigeration (VCR): uses mechanical energy • Vapour Absorption Refrigeration (VAR): uses thermal energy
11
Types of Refrigeration Vapour Compression Refrigeration • Highly compressed fluids tend to get colder when allowed to expand • If pressure high enough • Compressed air hotter than source of cooling • Expanded gas cooler than desired cold temperature 12
Types of Refrigeration Vapour Compression Refrigeration Two advantages • Lot of heat can be removed (lot of thermal energy to change liquid to vapour) • Heat transfer rate remains high (temperature of working fluid much lower than what is being cooled) 13
Types of Refrigeration Vapour Compression Refrigeration Refrigeration cycle 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
14
Types of Refrigeration Low pressure liquid refrigerant in evaporator Vapour Compression absorbs heat and changes toRefrigeration a gas cycle
Refrigeration 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
15
Types of Refrigeration The superheated vapour enters the compressor Vapour Compression where its pressure is raised Refrigeration cycle
Refrigeration 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
16
Types of Refrigeration The high pressure superheated gas is cooled in several stages Vapour Compression in the condenser
Refrigeration
Refrigeration cycle
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
17
Types of Refrigeration Vapour
Liquid passes through expansion device, which reduces its Compression Refrigeration pressure and controls the flow into the evaporator
Refrigeration cycle
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
18
Types of Refrigeration Vapour Compression Refrigeration Type of refrigerant • Refrigerant determined by the required cooling temperature • Chlorinated fluorocarbons (CFCs) or freons: R-11, R-12, R-21, R-22 and R502 19
Types of Refrigeration Vapour Compression Refrigeration Choice of compressor, design of condenser, evaporator determined by • Refrigerant • Required cooling • Load • Ease of maintenance • Physical space requirements • Availability of utilities (water, power)
20
Types of Refrigeration Vapour Absorption Refrigeration Condenser
Generator Hot Side
Evaporator Cold Side
Absorber
21
Types of Refrigeration Vapour Absorption Refrigeration
22
Types of Refrigeration Vapour Absorption Refrigeration
23
Types of Refrigeration
24
Types of Refrigeration Vapour Absorption Refrigeration
25
Types of Refrigeration Refrigerant-absorbent combinations for VARS The desirable properties of refrigerant-absorbent mixtures for VARS are: i The refrigerant should exhibit high solubility with solution in the absorber. This is to say that it should exhibit negative deviation from Raoult’s law at absorber. ii.
There should be large difference in the boiling points of refrigerant and absorbent (greater than 200 oC), so that only refrigerant is boiled-off in the generator. This ensures that only pure refrigerant circulates through refrigerant circuit (condenser-expansion valve-evaporator) leading to isothermal heat transfer in evaporator and condenser. 26
Types of Refrigeration iii.
It should exhibit small heat of mixing so that a high COP can be achieved. However, this requirement contradicts the first requirement. Hence, in practice a trade-off is required between solubility and heat of mixing.
iv.
The refrigerant-absorbent mixture should have high thermal conductivity and low viscosity for high performance.
v.
It should not undergo crystallization or solidification inside the system.
vi. The mixture should be safe, chemically stable, noncorrosive, inexpensive and should be available easily. 27
Types of Refrigeration The most commonly used refrigerant-absorbent pairs in commercial systems are: 1. Water-Lithium Bromide (H2O-LiBr) system for above 0oC applications such as air conditioning. Here water is the refrigerant and lithium bromide is the absorbent. 2. Ammonia-Water (NH3-H2O) system for refrigeration applications with ammonia as refrigerant and water as absorbent. Of late efforts are being made to develop other refrigerantabsorbent systems using both natural and synthetic refrigerants to overcome some of the limitations of (H 2O-LiBr) and (NH3-H2 O) systems. Currently, large water-lithium bromide (H2O-LiBr) systems are extensively used in air conditioning applications, where as large ammonia-water (NH3-H2O) systems are used in refrigeration applications, while small ammonia-water systems with a third inert gas are used in a pumpless form in small domestic refrigerators (triple fluid vapour absorption systems).
28
Types of Refrigeration Evaporative Cooling •
Air in contact with water to cool it close to ‘wet bulb temperature’
•
Advantage: efficient cooling at low cost
•
Disadvantage: air is rich in moisture Sprinkling Water
Hot Air
Cold Air
(Adapted from Munters, 2001) 29
Applied Psychrometric Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
30
Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
63
Heat Load Calculation Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
64
Heat Load Calculation
65
Heat Load Calculation
66
Heat Load Calculation
67
Heat Load Calculation
68
Heat Load Calculation
69
Heat Load Calculation
70
Heat Load Calculation
71
Heat Load Calculation
72
Heat Load Calculation
73
Heat Load Calculation
74
Heat Load Calculation
75
Heat Load Calculation
76
Heat Load Calculation
77
Heat Load Calculation
78
Heat Load Calculation
79
Heat Load Calculation
80
Heat Load Calculation
81
Heat Load Calculation
82
Heat Load Calculation
83
Heat Load Calculation
84
Heat Load Calculation
85
Air Duct Design Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
86
Air Duct Design
87
Air Duct Design
88
Air Duct Design
89
Air Duct Design
90
Air Duct Design
91
Air Duct Design TABLE 7 – RECOMMENDED MAXIMUM DUCT VELOCITIES FOR LOW VELOCITY SYSTEMS (FPM)
92
Air Duct Design
93
Air Duct Design
94
Air Duct Design
95
Air Duct Design
96
Air Duct Design
97
Air Duct Design
98
Air Duct Design Methods of Duct Design 1- Equal friction Method 2- Static Regain Method 1-Equal Friction Method This method of sizing is used for supply, exhaust and return air duct systems and employs the same friction loll per foot of length for the entire system. The equal friction method is superior to velocity reduction since it requires less balancing for symmetrical layouts. If a design has a 99
Air Duct Design
mixture of short and long runs, the shortest run requires considerable dampering. Such a system is difficult to balance since the equal friction method makes no provision for equalizing pressure drops in branches of for providing the same static pressure behind each air terminal.
100
Air Duct Design Example 4 – Equal Friction Method of Designing Ducts Given: Duct systems for general office (Fig.47). Total air quantity – 5400 cfm 18 air terminals – 300 cfm each Operating pressure forall terminals – 0.15 in. wg Radius elbows, R/D = 1.25 Find: 1.Initial duct velocity, area, size and friction rate in the duct section from the fan to the first branch. 2.Size of remaining duct runs. 3. Total equivalent length of duct run with highest resistance. 4. Total static pressure required at fan discharge 101
Air Duct Design 2-Static Regain Method The basic principle of the static regain method is to size a duct run so that the increase in static pressure (regain due to reduction in velocity) at each branch or air terminal just offsets the friction loss in the succeeding section of duct. The static pressure is then the same before each terminal and at each branch. The following procedure is used to design a duct system by this method: select a starting velocity at the fan discharge from Table 7 and size the initial duct section from Table 6.
102
Air Duct Design The remaining sections of duct are sized from Chart 10 (L!Q Ratio) and Chart 11 (Low Velocity Static Regain). Chart 10 is used to determine the L/Q ratio knowing the air quantity (Q) and length (L) between outlets or branches in the duct section to be sized by static regain. This length (L) is the equivalent length between the outlets or branches, including elbows, except transformations. The effect of the transformation section is accounted for in “Chart 11 3 Static Regain.” This assumes that the transformation section is laid out according to the recommendation presented in this chapter.
103
Air Duct Design
104
Pressurization System Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
105
Pressurization System STAIRCASE PRESSURIZATION CALCULATION FOR BASEMENT PART - A BASEMENT TO GROUND FLOOR) Q1
=
Kf A √ Δ P
Q1
=
Air Leakage in Cu. M./ Sec.
A
=
Area of Leakage in Sq.M.
ΔP
=
Pressure Difference in Pascal ( 50 Pa)
Kf
=
Coefficient 0.839
No. of Floors
=
Basement to Ground Floor = 2
No. of Doors
=
2
Door Size
=
1.2 M x 2.1 M
Gap Between door and Frame/Floor
=
6 mm at Top and on side
=
15 mm at Bottom
=
2 x H x gap (side) + 1 x W x gap (Top) + 1 x W x gap (Bottom )
=
2 x 2.1 x 6/1000 + 1 x 1.2 x 6/1000 + 1 x 1.2 x 15/1000
=
0.0252 + 0.0072 + 0.018
=
0.0504 Sq. M.
Area of Leakage Between Door & Frame
106
Pressurization System
Area of Leakage in Closed Condition/Door
=
0.0504 Sq. M.
Total Leakage Area for 2 No. Doors
=
0.0504 x 2
=
0.10 Sq.M.
=
0.839 x 0.10 x √ 50
=
0.60 Cu. M/Sec.
=
1270 CFM
Q1
Leakage of Air Thru 2 No. Open Door ( 1 No. at affected floor + 1 No. at Exit to Building ) Q2
Total Required Air Quantity
=
Area of Doors x Velocity
=
2.1 x 1.2 x2 No. x 1.0 M/sec.
=
5.04 Cu. M./Sec
=
10671 CFM
=
Q1 + Q2
=
1270 + 10671
=
11941 CFM
107
Pressurization System LIFT WELL PRESSURIZATION CALCULATION TOWER T1 (G+13)- 5 Nos. Q
=
Kf A √ Δ P
Q
=
Air Leakage in Cu. M./ Sec.
A
=
Area of Leakage in Sq.M.
ΔP
=
Pressure Difference in Pascal ( 50 Pa)
Kf
=
Coefficient 0.839
No. of Floors
=
Lower Basement (Part-A) to 13th Floor = 16
No. of Doors
=
16
Door Size
=
2.1 M x 1.2 M
Area of Leakage Between Lift Door & Wall/ Door
=
0.065 Sq. M.
Total Leakage Area for 16 No. Doors
=
0.065 x 16
=
1.04 Sq.M.
=
0.839 x 1.04 x √ 50
=
6.17 Cu. M/Sec.
=
13063 CFM
=
13063x2
=
26126 CFM
=
26500 CFM
Q
Fan Capacity for Two Lift Well
Say 1 No. 26500 CFM DIDW Centrifugal Fan Section For Fresh Air Supply
108
Chilled/Condenser Water Piping Design Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
109
Chilled/Condenser Water Piping Design
110
Chilled/Condenser Water Piping Design
111
Chilled/Condenser Water Piping Design
112
Chilled/Condenser Water Piping Design
113
Chilled/Condenser Water Piping Design
114
Chilled/Condenser Water Piping Design
115
Chilled/Condenser Water Piping Design
116
Chilled/Condenser Water Piping Design
117
Chilled/Condenser Water Piping Design
118
Chilled/Condenser Water Piping Design
119
Chilled/Condenser Water Piping Design
120
Chilled/Condenser Water Piping Design
121
Chilled/Condenser Water Piping Design
122
Compressors Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
123
Compressors
124
Compressors
125
Compressors
126
Compressors
127
Compressors
128
Compressors
129
Compressors
130
Compressors
131
Compressors
132
Compressors
133
Compressors
134
Compressors
135
Condensers & Evaporators Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
136
Condensers & Evaporators
137
Condensers & Evaporators
138
Condensers & Evaporators
139
Condensers & Evaporators
140
Condensers & Evaporators
141
Condensers & Evaporators
142
Condensers & Evaporators
143
Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
149
Condensers & Evaporators
150
Condensers & Evaporators
151
Condensers & Evaporators
152
Condensers & Evaporators
153
Condensers & Evaporators
154
Condensers & Evaporators
155
Condensers & Evaporators
156
Condensers & Evaporators
157
Condensers & Evaporators
158
Condensers & Evaporators
159
Condensers & Evaporators
160
Condensers & Evaporators
161
Expansion Devices Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
162
Expansion Devices
163
Expansion Devices
164
Expansion Devices
165
Expansion Devices
166
Expansion Devices
167
Cooling Tower Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of Refrigeration and AC Energy efficiency opportunities
168
Cooling Tower
169
Cooling Tower
170
Cooling Tower
171
Cooling Tower
172
Cooling Tower
173
Cooling Tower
174
Cooling Tower
175
Cooling Tower
176
Cooling Tower
177
Cooling Tower
178
Cooling Tower
179
Cooling Tower
180
Cooling Tower
181
Cooling Tower
182
Cooling Tower
183
Cooling Tower
184
Cooling Tower
185
Cooling Tower
186
Cooling Tower
187
Cooling Tower
188
Cooling Tower
189
Cooling Tower
190
Cooling Tower
191
Cooling Tower
192
Cooling Tower
193
Cooling Tower
194
Cooling Tower
195
Cooling Tower
196
Cooling Tower
197
Cooling Tower
198
Cooling Tower
199
Cooling Tower
200
Cooling Tower
201
Cooling Tower
202
Assessment of Refrigeration and AC Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of Refrigeration and AC Energy efficiency opportunities
203
Assessment of Refrigeration and AC Assessment of Refrigeration • Cooling effect: Tons of Refrigeration 1 TR = 3024 kCal/hr heat rejected
• TR is assessed as: TR = Q x⋅Cp x⋅ (Ti – To) / 3024 Q= Cp = Ti = To =
mass flow rate of coolant in kg/hr is coolant specific heat in kCal /kg deg C inlet, temperature of coolant to evaporator (chiller) in 0C outlet temperature of coolant from evaporator (chiller) in 0C
204
Assessment of Refrigeration and AC Assessment of Refrigeration Specific Power Consumption (kW/TR) • Indicator of refrigeration system’s performance • kW/TR of centralized chilled water system is sum of • Compressor kW/TR • Chilled water pump kW/TR • Condenser water pump kW/TR • Cooling tower fan kW/TR
205
Assessment of Refrigeration and AC Assessment of Refrigeration Coefficient of Performance (COPCarnot) •
Standard measure of refrigeration efficiency
•
Depends on evaporator temperature Te and condensing temperature Tc: COPCarnot
•
=
Te / (Tc - Te)
COP in industry calculated for type of compressor: COP =
Cooling effect (kW) Power input to compressor (kW)
206
Assessment of Refrigeration and AC Assessment of Refrigeration
COP increases with rising evaporator temperature (Te)
COP increases with decreasing condensing temperature (Tc)
207
Assessment of Refrigeration and AC Assessment of Air Conditioning Measure •
Airflow Q (m3/s) at Fan Coil Units (FCU) or Air Handling Units (AHU): anemometer
•
Air density ρ (kg/m3)
•
Dry bulb and wet bulb temperature: psychrometer
•
Enthalpy (kCal/kg) of inlet air (hin) and outlet air (Hout): psychrometric charts
Calculate TR
TR =
Q × ρ × ( h in − h out ) 3024 208
Assessment of Refrigeration and AC Assessment of Air Conditioning Indicative TR load profile • Small office cabins: 0.1 TR/m2 • Medium size office (10 – 30 people occupancy) with central A/C: 0.06 TR/m2 • Large multistoried office complexes with central A/C: 0.04 TR/m2 209
Assessment of Refrigeration and AC Considerations for Assessment • Accuracy of measurements • Inlet/outlet temp of chilled and condenser water • Flow of chilled and condenser water
• Integrated Part Load Value (IPLV) • kW/TR for 100% load but most equipment operate between 50-75% of full load • IPLV calculates kW/TR with partial loads • Four points in cycle: 100%, 75%, 50%, 25%
210
Energy Efficiency Opportunities Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of Refrigeration and AC Energy Efficiency Opportunities
211
Energy Efficiency Opportunities 1. Optimize process heat exchange 2. Maintain heat exchanger surfaces 3. Multi-staging systems 4. Matching capacity to system load 5. Capacity control of compressors 6. Multi-level refrigeration for plant needs 7. Chilled water storage 8. System design features
212
Energy Efficiency Opportunities 1. Optimize Process Heat Exchange High compressor safety margins: energy loss 1. Proper sizing heat transfer areas of heat exchangers and evaporators • Heat transfer coefficient on refrigerant side: 1400 – 2800 Watt/m2K • Heat transfer area refrigerant side: >0.5 m2/TR
2. Optimum driving force (difference Te and Tc): 1oC raise in Te = 3% power savings 213
Energy Efficiency Opportunities 1. Optimize Process Heat Exchange Evaporator Temperature (0C)
Refrigeration Capacity*(tons)
Specific Power Consumption (kW/TR)
Increase kW/TR (%)
5.0
67.58
0.81
-
0.0
56.07
0.94
16.0
-5.0
45.98
1.08
33.0
-10.0
37.20
1.25
54.0
-20.0
23.12
1.67
106.0
(National Productivity Council)
Condenser temperature 40◦C
Condensing Temperature (0C)
Refrigeration Capacity (tons)
Specific Power Consumption (kW /TR)
Increase kW/TR (%)
26.7
31.5
1.17
-
35.0
21.4
1.27
8.5
40.0
20.0
1.41
20.5
*Reciprocating compressor using R-22 refrigerant. Evaporator temperature.-10◦ C
214
Energy Efficiency Opportunities 1. Optimize Process Heat Exchange 3. Selection of condensers • Options: • • •
Air cooled condensers Air-cooled with water spray condensers Shell & tube condensers with water-cooling
• Water-cooled shell & tube condenser • • •
Lower discharge pressure Higher TR Lower power consumption
215
Energy Efficiency Opportunities 2. Maintain Heat Exchanger Surfaces • Poor maintenance = increased power consumption • Maintain condensers and evaporators • Separation of lubricating oil and refrigerant • Timely defrosting of coils • Increased velocity of secondary coolant
• Maintain cooling towers • 0.55◦C reduction in returning water from cooling tower = 3.0 % reduced power
216
Energy Efficiency Opportunities 2. Maintain Heat Exchanger Surfaces Effect of poor maintenance on compressor power consumption Te (0C)
Tc (0C)
Refrigeration Capacity* (TR)
Specific Power Consumption (kW/TR)
Normal
7.2
40.5
17.0
0.69
-
Dirty condenser
7.2
46.1
15.6
0.84
20.4
Dirty evaporator
1.7
40.5
13.8
0.82
18.3
Dirty condenser and evaporator
1.7
46.1
12.7
0.96
38.7
Condition
(National Productivity Council)
Increase kW/TR (%)
Energy Efficiency Opportunities 3. Multi-Staging Systems • Suited for • Low temp applications with high compression • Wide temperature range • Two types for all compressor types • Compound • Cascade 218
Energy Efficiency Opportunities 3. Multi-Stage Systems a. Compound •
Two low compression ratios = 1 high
•
First stage compressor meets cooling load
•
Second stage compressor meets load evaporator and flash gas
•
Single refrigerant
b. Cascade •
Preferred for -46 oC to -101oC
•
Two systems with different refrigerants
219
Energy Efficiency Opportunities 4. Matching Capacity to Load System • Most applications have varying loads • Consequence of part-load operation • COP increases • but lower efficiency
• Match refrigeration capacity to load requires knowledge of • Compressor performance • Variations in ambient conditions • Cooling load
220
Energy Efficiency Opportunities 5. Capacity Control of Compressors • Cylinder unloading, vanes, valves • Reciprocating compressors: step-by-step through cylinder unloading:
• Centrifugal compressors: continuous modulation through vane control • Screw compressors: sliding valves
• Speed control • Reciprocating compressors: ensure lubrication system is not affected • Centrifugal compressors: >50% of capacity
221
Energy Efficiency Opportunities 5. Capacity Control of Compressors • Temperature monitoring • Reciprocating compressors: return water (if varying loads), water leaving chiller (constant loads) • Centrifugal compressors: outgoing water temperature • Screw compressors: outgoing water temperature
• Part load applications: screw compressors more efficient
222
Energy Efficiency Opportunities 6. Multi-Level Refrigeration Bank of compressors at central plant •
Monitor cooling and chiller load: 1 chiller full load more efficient than 2 chillers at part-load
•
Distribution system: individual chillers feed all branch lines; Isolation valves; Valves to isolate sections
•
Load individual compressors to full capacity before operating second compressor
•
Provide smaller capacity chiller to meet peak demands
223
Energy Efficiency Opportunities 6. Multi-Level Refrigeration Packaged units (instead of central plant) • Diverse applications with wide temp range and long distance • Benefits: economical, flexible and reliable • Disadvantage: central plants use less power
Flow control • Reduced flow • Operation at normal flow with shut-off periods 224
Energy Efficiency Opportunities 7. Chilled Water Storage • Chilled water storage facility with insulation • Suited only if temp variations are acceptable • Economical because • Chillers operate during low peak demand hours: reduced peak demand charges • Chillers operate at nighttime: reduced tariffs 225 and improved COP
Energy Efficiency Opportunities 8. System Design Features • FRP impellers, film fills, PVC drift eliminators • Softened water for condensers • Economic insulation thickness • Roof coatings and false ceilings • Energy efficient heat recovery devices • Variable air volume systems • Sun film application for heat reflection • Optimizing lighting loads
226
Training Session on Energy Equipment
Refrigeration & Air Conditioning Systems THANK YOU FOR YOUR ATTENTION
227
Refrigeration & Air Conditioning Presentation by
“Mohammad Salim” M/s Unitech Ltd., Gurgaon. 1
Training Agenda: Refrigeration & Air Conditioning Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
2
Introduction How does it work?
High Temperature Reservoir Heat Rejected R
Work Input
Heat Absorbed Low Temperature Reservoir 3
Introduction How does it work? Thermal energy moves from left to right through five loops of heat transfer: 1)
2)
3)
4)
5)
Indoor air loop
Chilled water loop
Refrigerant loop
Condenser water loop
Cooling water loop
(Bureau of Energy Efficiency, 2004)
4
Introduction AC Systems AC options / combinations: • Air Conditioning (for comfort / machine) • Split air conditioners • VRV System in Group Housing etc. • Fan coil units in a larger system • Air handling units in a larger system • Evaporating Cooling in a larger system
5
Introduction Refrigeration systems for industrial processes • Small capacity modular units of direct expansion type (50 Tons of Refrigeration) • Centralized chilled water plants with chilled water as a secondary coolant
(50 –
250 TR)
• Brine plants with brines as lower temperature, secondary coolant (>250 TR) 6
Introduction Refrigeration at large companies • Bank of units off-site with common • Chilled water pumps • Condenser water pumps • Cooling towers
• More levels of refrigeration/AC, e.g. • Comfort air conditioning (20-25 oC) • Chilled water system (8 – 10 oC) • Brine system (< 0 oC)
7
Reference Handbooks/Standards Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
8
Reference Handbooks/Standards ASHRAE Handbook of Fundamentals ASHRAE Handbook of Refrigeration ASHRAE Handbook of Application ASHRAE Handbook of System & Equipments ASHRAE Standards 62.1 ASHRAE Standards 90.1 ISHRAE Weather Data Carrier Handbook NBC-2005 LEED-2009 NFPA-92A ECBC-2007 Heat and Mass Transfer SMACNA Standard Indian Standards
9
Types of Refrigeration Introduction Reference Handbooks/Standards Types of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
10
Types of Refrigeration Refrigeration systems • Vapour Compression Refrigeration (VCR): uses mechanical energy • Vapour Absorption Refrigeration (VAR): uses thermal energy
11
Types of Refrigeration Vapour Compression Refrigeration • Highly compressed fluids tend to get colder when allowed to expand • If pressure high enough • Compressed air hotter than source of cooling • Expanded gas cooler than desired cold temperature 12
Types of Refrigeration Vapour Compression Refrigeration Two advantages • Lot of heat can be removed (lot of thermal energy to change liquid to vapour) • Heat transfer rate remains high (temperature of working fluid much lower than what is being cooled) 13
Types of Refrigeration Vapour Compression Refrigeration Refrigeration cycle 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
14
Types of Refrigeration Low pressure liquid refrigerant in evaporator Vapour Compression absorbs heat and changes toRefrigeration a gas cycle
Refrigeration 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
15
Types of Refrigeration The superheated vapour enters the compressor Vapour Compression where its pressure is raised Refrigeration cycle
Refrigeration 3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
16
Types of Refrigeration The high pressure superheated gas is cooled in several stages Vapour Compression in the condenser
Refrigeration
Refrigeration cycle
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
17
Types of Refrigeration Vapour
Liquid passes through expansion device, which reduces its Compression Refrigeration pressure and controls the flow into the evaporator
Refrigeration cycle
3
Condenser
High Pressure Side
4 Expansion Device
Compressor
2
1 Evaporator
Low Pressure Side
18
Types of Refrigeration Vapour Compression Refrigeration Type of refrigerant • Refrigerant determined by the required cooling temperature • Chlorinated fluorocarbons (CFCs) or freons: R-11, R-12, R-21, R-22 and R502 19
Types of Refrigeration Vapour Compression Refrigeration Choice of compressor, design of condenser, evaporator determined by • Refrigerant • Required cooling • Load • Ease of maintenance • Physical space requirements • Availability of utilities (water, power)
20
Types of Refrigeration Vapour Absorption Refrigeration Condenser
Generator Hot Side
Evaporator Cold Side
Absorber
21
Types of Refrigeration Vapour Absorption Refrigeration
22
Types of Refrigeration Vapour Absorption Refrigeration
23
Types of Refrigeration
24
Types of Refrigeration Vapour Absorption Refrigeration
25
Types of Refrigeration Refrigerant-absorbent combinations for VARS The desirable properties of refrigerant-absorbent mixtures for VARS are: i The refrigerant should exhibit high solubility with solution in the absorber. This is to say that it should exhibit negative deviation from Raoult’s law at absorber. ii.
There should be large difference in the boiling points of refrigerant and absorbent (greater than 200 oC), so that only refrigerant is boiled-off in the generator. This ensures that only pure refrigerant circulates through refrigerant circuit (condenser-expansion valve-evaporator) leading to isothermal heat transfer in evaporator and condenser. 26
Types of Refrigeration iii.
It should exhibit small heat of mixing so that a high COP can be achieved. However, this requirement contradicts the first requirement. Hence, in practice a trade-off is required between solubility and heat of mixing.
iv.
The refrigerant-absorbent mixture should have high thermal conductivity and low viscosity for high performance.
v.
It should not undergo crystallization or solidification inside the system.
vi. The mixture should be safe, chemically stable, noncorrosive, inexpensive and should be available easily. 27
Types of Refrigeration The most commonly used refrigerant-absorbent pairs in commercial systems are: 1. Water-Lithium Bromide (H2O-LiBr) system for above 0oC applications such as air conditioning. Here water is the refrigerant and lithium bromide is the absorbent. 2. Ammonia-Water (NH3-H2O) system for refrigeration applications with ammonia as refrigerant and water as absorbent. Of late efforts are being made to develop other refrigerantabsorbent systems using both natural and synthetic refrigerants to overcome some of the limitations of (H 2O-LiBr) and (NH3-H2 O) systems. Currently, large water-lithium bromide (H2O-LiBr) systems are extensively used in air conditioning applications, where as large ammonia-water (NH3-H2O) systems are used in refrigeration applications, while small ammonia-water systems with a third inert gas are used in a pumpless form in small domestic refrigerators (triple fluid vapour absorption systems).
28
Types of Refrigeration Evaporative Cooling •
Air in contact with water to cool it close to ‘wet bulb temperature’
•
Advantage: efficient cooling at low cost
•
Disadvantage: air is rich in moisture Sprinkling Water
Hot Air
Cold Air
(Adapted from Munters, 2001) 29
Applied Psychrometric Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
30
Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Applied Psychrometric
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Heat Load Calculation Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
64
Heat Load Calculation
65
Heat Load Calculation
66
Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
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Heat Load Calculation
84
Heat Load Calculation
85
Air Duct Design Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
86
Air Duct Design
87
Air Duct Design
88
Air Duct Design
89
Air Duct Design
90
Air Duct Design
91
Air Duct Design TABLE 7 – RECOMMENDED MAXIMUM DUCT VELOCITIES FOR LOW VELOCITY SYSTEMS (FPM)
92
Air Duct Design
93
Air Duct Design
94
Air Duct Design
95
Air Duct Design
96
Air Duct Design
97
Air Duct Design
98
Air Duct Design Methods of Duct Design 1- Equal friction Method 2- Static Regain Method 1-Equal Friction Method This method of sizing is used for supply, exhaust and return air duct systems and employs the same friction loll per foot of length for the entire system. The equal friction method is superior to velocity reduction since it requires less balancing for symmetrical layouts. If a design has a 99
Air Duct Design
mixture of short and long runs, the shortest run requires considerable dampering. Such a system is difficult to balance since the equal friction method makes no provision for equalizing pressure drops in branches of for providing the same static pressure behind each air terminal.
100
Air Duct Design Example 4 – Equal Friction Method of Designing Ducts Given: Duct systems for general office (Fig.47). Total air quantity – 5400 cfm 18 air terminals – 300 cfm each Operating pressure forall terminals – 0.15 in. wg Radius elbows, R/D = 1.25 Find: 1.Initial duct velocity, area, size and friction rate in the duct section from the fan to the first branch. 2.Size of remaining duct runs. 3. Total equivalent length of duct run with highest resistance. 4. Total static pressure required at fan discharge 101
Air Duct Design 2-Static Regain Method The basic principle of the static regain method is to size a duct run so that the increase in static pressure (regain due to reduction in velocity) at each branch or air terminal just offsets the friction loss in the succeeding section of duct. The static pressure is then the same before each terminal and at each branch. The following procedure is used to design a duct system by this method: select a starting velocity at the fan discharge from Table 7 and size the initial duct section from Table 6.
102
Air Duct Design The remaining sections of duct are sized from Chart 10 (L!Q Ratio) and Chart 11 (Low Velocity Static Regain). Chart 10 is used to determine the L/Q ratio knowing the air quantity (Q) and length (L) between outlets or branches in the duct section to be sized by static regain. This length (L) is the equivalent length between the outlets or branches, including elbows, except transformations. The effect of the transformation section is accounted for in “Chart 11 3 Static Regain.” This assumes that the transformation section is laid out according to the recommendation presented in this chapter.
103
Air Duct Design
104
Pressurization System Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
105
Pressurization System STAIRCASE PRESSURIZATION CALCULATION FOR BASEMENT PART - A BASEMENT TO GROUND FLOOR) Q1
=
Kf A √ Δ P
Q1
=
Air Leakage in Cu. M./ Sec.
A
=
Area of Leakage in Sq.M.
ΔP
=
Pressure Difference in Pascal ( 50 Pa)
Kf
=
Coefficient 0.839
No. of Floors
=
Basement to Ground Floor = 2
No. of Doors
=
2
Door Size
=
1.2 M x 2.1 M
Gap Between door and Frame/Floor
=
6 mm at Top and on side
=
15 mm at Bottom
=
2 x H x gap (side) + 1 x W x gap (Top) + 1 x W x gap (Bottom )
=
2 x 2.1 x 6/1000 + 1 x 1.2 x 6/1000 + 1 x 1.2 x 15/1000
=
0.0252 + 0.0072 + 0.018
=
0.0504 Sq. M.
Area of Leakage Between Door & Frame
106
Pressurization System
Area of Leakage in Closed Condition/Door
=
0.0504 Sq. M.
Total Leakage Area for 2 No. Doors
=
0.0504 x 2
=
0.10 Sq.M.
=
0.839 x 0.10 x √ 50
=
0.60 Cu. M/Sec.
=
1270 CFM
Q1
Leakage of Air Thru 2 No. Open Door ( 1 No. at affected floor + 1 No. at Exit to Building ) Q2
Total Required Air Quantity
=
Area of Doors x Velocity
=
2.1 x 1.2 x2 No. x 1.0 M/sec.
=
5.04 Cu. M./Sec
=
10671 CFM
=
Q1 + Q2
=
1270 + 10671
=
11941 CFM
107
Pressurization System LIFT WELL PRESSURIZATION CALCULATION TOWER T1 (G+13)- 5 Nos. Q
=
Kf A √ Δ P
Q
=
Air Leakage in Cu. M./ Sec.
A
=
Area of Leakage in Sq.M.
ΔP
=
Pressure Difference in Pascal ( 50 Pa)
Kf
=
Coefficient 0.839
No. of Floors
=
Lower Basement (Part-A) to 13th Floor = 16
No. of Doors
=
16
Door Size
=
2.1 M x 1.2 M
Area of Leakage Between Lift Door & Wall/ Door
=
0.065 Sq. M.
Total Leakage Area for 16 No. Doors
=
0.065 x 16
=
1.04 Sq.M.
=
0.839 x 1.04 x √ 50
=
6.17 Cu. M/Sec.
=
13063 CFM
=
13063x2
=
26126 CFM
=
26500 CFM
Q
Fan Capacity for Two Lift Well
Say 1 No. 26500 CFM DIDW Centrifugal Fan Section For Fresh Air Supply
108
Chilled/Condenser Water Piping Design Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
109
Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Chilled/Condenser Water Piping Design
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Compressors Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
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Compressors
124
Compressors
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Compressors
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Compressors
127
Compressors
128
Compressors
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Compressors
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Compressors
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Compressors
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Compressors
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Compressors
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Compressors
135
Condensers & Evaporators Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
136
Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Condensers & Evaporators
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Expansion Devices Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of refrigeration and AC Energy efficiency opportunities
162
Expansion Devices
163
Expansion Devices
164
Expansion Devices
165
Expansion Devices
166
Expansion Devices
167
Cooling Tower Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of Refrigeration and AC Energy efficiency opportunities
168
Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
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Cooling Tower
202
Assessment of Refrigeration and AC Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of Refrigeration and AC Energy efficiency opportunities
203
Assessment of Refrigeration and AC Assessment of Refrigeration • Cooling effect: Tons of Refrigeration 1 TR = 3024 kCal/hr heat rejected
• TR is assessed as: TR = Q x⋅Cp x⋅ (Ti – To) / 3024 Q= Cp = Ti = To =
mass flow rate of coolant in kg/hr is coolant specific heat in kCal /kg deg C inlet, temperature of coolant to evaporator (chiller) in 0C outlet temperature of coolant from evaporator (chiller) in 0C
204
Assessment of Refrigeration and AC Assessment of Refrigeration Specific Power Consumption (kW/TR) • Indicator of refrigeration system’s performance • kW/TR of centralized chilled water system is sum of • Compressor kW/TR • Chilled water pump kW/TR • Condenser water pump kW/TR • Cooling tower fan kW/TR
205
Assessment of Refrigeration and AC Assessment of Refrigeration Coefficient of Performance (COPCarnot) •
Standard measure of refrigeration efficiency
•
Depends on evaporator temperature Te and condensing temperature Tc: COPCarnot
•
=
Te / (Tc - Te)
COP in industry calculated for type of compressor: COP =
Cooling effect (kW) Power input to compressor (kW)
206
Assessment of Refrigeration and AC Assessment of Refrigeration
COP increases with rising evaporator temperature (Te)
COP increases with decreasing condensing temperature (Tc)
207
Assessment of Refrigeration and AC Assessment of Air Conditioning Measure •
Airflow Q (m3/s) at Fan Coil Units (FCU) or Air Handling Units (AHU): anemometer
•
Air density ρ (kg/m3)
•
Dry bulb and wet bulb temperature: psychrometer
•
Enthalpy (kCal/kg) of inlet air (hin) and outlet air (Hout): psychrometric charts
Calculate TR
TR =
Q × ρ × ( h in − h out ) 3024 208
Assessment of Refrigeration and AC Assessment of Air Conditioning Indicative TR load profile • Small office cabins: 0.1 TR/m2 • Medium size office (10 – 30 people occupancy) with central A/C: 0.06 TR/m2 • Large multistoried office complexes with central A/C: 0.04 TR/m2 209
Assessment of Refrigeration and AC Considerations for Assessment • Accuracy of measurements • Inlet/outlet temp of chilled and condenser water • Flow of chilled and condenser water
• Integrated Part Load Value (IPLV) • kW/TR for 100% load but most equipment operate between 50-75% of full load • IPLV calculates kW/TR with partial loads • Four points in cycle: 100%, 75%, 50%, 25%
210
Energy Efficiency Opportunities Introduction Reference Handbooks/Standards Type of refrigeration Applied Psychrometric Heat Load Calculation Air Duct Design Pressurization System Chilled/Condenser Water Piping Design Compressors Condensers & Evaporators Expansion Devices Cooling Tower Assessment of Refrigeration and AC Energy Efficiency Opportunities
211
Energy Efficiency Opportunities 1. Optimize process heat exchange 2. Maintain heat exchanger surfaces 3. Multi-staging systems 4. Matching capacity to system load 5. Capacity control of compressors 6. Multi-level refrigeration for plant needs 7. Chilled water storage 8. System design features
212
Energy Efficiency Opportunities 1. Optimize Process Heat Exchange High compressor safety margins: energy loss 1. Proper sizing heat transfer areas of heat exchangers and evaporators • Heat transfer coefficient on refrigerant side: 1400 – 2800 Watt/m2K • Heat transfer area refrigerant side: >0.5 m2/TR
2. Optimum driving force (difference Te and Tc): 1oC raise in Te = 3% power savings 213
Energy Efficiency Opportunities 1. Optimize Process Heat Exchange Evaporator Temperature (0C)
Refrigeration Capacity*(tons)
Specific Power Consumption (kW/TR)
Increase kW/TR (%)
5.0
67.58
0.81
-
0.0
56.07
0.94
16.0
-5.0
45.98
1.08
33.0
-10.0
37.20
1.25
54.0
-20.0
23.12
1.67
106.0
(National Productivity Council)
Condenser temperature 40◦C
Condensing Temperature (0C)
Refrigeration Capacity (tons)
Specific Power Consumption (kW /TR)
Increase kW/TR (%)
26.7
31.5
1.17
-
35.0
21.4
1.27
8.5
40.0
20.0
1.41
20.5
*Reciprocating compressor using R-22 refrigerant. Evaporator temperature.-10◦ C
214
Energy Efficiency Opportunities 1. Optimize Process Heat Exchange 3. Selection of condensers • Options: • • •
Air cooled condensers Air-cooled with water spray condensers Shell & tube condensers with water-cooling
• Water-cooled shell & tube condenser • • •
Lower discharge pressure Higher TR Lower power consumption
215
Energy Efficiency Opportunities 2. Maintain Heat Exchanger Surfaces • Poor maintenance = increased power consumption • Maintain condensers and evaporators • Separation of lubricating oil and refrigerant • Timely defrosting of coils • Increased velocity of secondary coolant
• Maintain cooling towers • 0.55◦C reduction in returning water from cooling tower = 3.0 % reduced power
216
Energy Efficiency Opportunities 2. Maintain Heat Exchanger Surfaces Effect of poor maintenance on compressor power consumption Te (0C)
Tc (0C)
Refrigeration Capacity* (TR)
Specific Power Consumption (kW/TR)
Normal
7.2
40.5
17.0
0.69
-
Dirty condenser
7.2
46.1
15.6
0.84
20.4
Dirty evaporator
1.7
40.5
13.8
0.82
18.3
Dirty condenser and evaporator
1.7
46.1
12.7
0.96
38.7
Condition
(National Productivity Council)
Increase kW/TR (%)
Energy Efficiency Opportunities 3. Multi-Staging Systems • Suited for • Low temp applications with high compression • Wide temperature range • Two types for all compressor types • Compound • Cascade 218
Energy Efficiency Opportunities 3. Multi-Stage Systems a. Compound •
Two low compression ratios = 1 high
•
First stage compressor meets cooling load
•
Second stage compressor meets load evaporator and flash gas
•
Single refrigerant
b. Cascade •
Preferred for -46 oC to -101oC
•
Two systems with different refrigerants
219
Energy Efficiency Opportunities 4. Matching Capacity to Load System • Most applications have varying loads • Consequence of part-load operation • COP increases • but lower efficiency
• Match refrigeration capacity to load requires knowledge of • Compressor performance • Variations in ambient conditions • Cooling load
220
Energy Efficiency Opportunities 5. Capacity Control of Compressors • Cylinder unloading, vanes, valves • Reciprocating compressors: step-by-step through cylinder unloading:
• Centrifugal compressors: continuous modulation through vane control • Screw compressors: sliding valves
• Speed control • Reciprocating compressors: ensure lubrication system is not affected • Centrifugal compressors: >50% of capacity
221
Energy Efficiency Opportunities 5. Capacity Control of Compressors • Temperature monitoring • Reciprocating compressors: return water (if varying loads), water leaving chiller (constant loads) • Centrifugal compressors: outgoing water temperature • Screw compressors: outgoing water temperature
• Part load applications: screw compressors more efficient
222
Energy Efficiency Opportunities 6. Multi-Level Refrigeration Bank of compressors at central plant •
Monitor cooling and chiller load: 1 chiller full load more efficient than 2 chillers at part-load
•
Distribution system: individual chillers feed all branch lines; Isolation valves; Valves to isolate sections
•
Load individual compressors to full capacity before operating second compressor
•
Provide smaller capacity chiller to meet peak demands
223
Energy Efficiency Opportunities 6. Multi-Level Refrigeration Packaged units (instead of central plant) • Diverse applications with wide temp range and long distance • Benefits: economical, flexible and reliable • Disadvantage: central plants use less power
Flow control • Reduced flow • Operation at normal flow with shut-off periods 224
Energy Efficiency Opportunities 7. Chilled Water Storage • Chilled water storage facility with insulation • Suited only if temp variations are acceptable • Economical because • Chillers operate during low peak demand hours: reduced peak demand charges • Chillers operate at nighttime: reduced tariffs 225 and improved COP
Energy Efficiency Opportunities 8. System Design Features • FRP impellers, film fills, PVC drift eliminators • Softened water for condensers • Economic insulation thickness • Roof coatings and false ceilings • Energy efficient heat recovery devices • Variable air volume systems • Sun film application for heat reflection • Optimizing lighting loads
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Training Session on Energy Equipment
Refrigeration & Air Conditioning Systems THANK YOU FOR YOUR ATTENTION
227
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