Energy Conservation Refrigeration Systems
By J.ILANGUMARAN
REFRIGERATION SYSTEM
• Vapour compression refrigeration systems (VCR) and Vapour
absorption refrigeration systems (VAR) find wide usage in the Indian industry. • Although VCR's are dominating, over 1000 VAR's are in use in India. THE INDIAN SCENARIO SCENARIO--MAJOR -MAJOR ADVANCES
• Widely used in industrial cooling, food retail and air • • • • • •
conditioning applications. Cost savings of 25 % are easily available. Efficient operation of refrigeration systems depends depend s on the following factors : Design Selection Installation Use of the system
REFRIGERATION SYSTEM
• Vapour compression refrigeration systems (VCR) and Vapour
absorption refrigeration systems (VAR) find wide usage in the Indian industry. • Although VCR's are dominating, over 1000 VAR's are in use in India. THE INDIAN SCENARIO SCENARIO--MAJOR -MAJOR ADVANCES
• Widely used in industrial cooling, food retail and air • • • • • •
conditioning applications. Cost savings of 25 % are easily available. Efficient operation of refrigeration systems depends depend s on the following factors : Design Selection Installation Use of the system
REFRIGERATION SYSTEM
• The basic purpose of the refrigeration system is to control & •
maintain specified temperature. The temperature maintained can be from 10 C to 40 C or even less. °
°
Types of Refrigeration Systems
• • Vapour Absorption System Refrigerants R - 11, 11, R R - 12, 12, • Ammonia and various halo carbon compounds R
•
R R - 22 22 and an d R R - 502 502 for for (VCR) (VCR (V CR)) Lithium Bromide, Ammonia (for VAR)
REFRIGERATION SYSTEM Load or Source Evaporator Work
Expansion Device
Compressor Condenser Cooler Work
TECHNICAL TECHNIC AL COMPARISON COMPARISON OF VAPOUR VAPOUR ABSORPTION ABSORPTIO N CHILLER CHILLE R (VAC) (VAC) & VAPOUR COMPRESSIO COMPRESSION N CHILLER (VCR) VAC
VCR
Equipment :
Equipment :
Absorber, Generator, Condenser & Evaporator
Compressor, Condenser, Thermal Expansion Valve, Evaporat Evaporator or
Refrigerant : Water
Refrigerant : CFC, Ammonia gases etc.
Absorbent : LiBr
Absorbent : Not Applicable
Input Required : Steam
Input Required : Power
TECHNICAL COMPARISON OF VAC & VCR VAC Cycle :
VCR Cycle :
1. Take the latent heat from outside water 1. Take the latent heat from outside water (Chilled Water) in evaporator by (Chilled water) in evaporator by absorbent. refrigerant. . . . absorbent. compressed by compressor to high 3. These diluted absorbent is heated up temp. and higher pressure. and separate the refrigerant in the 3. These high temp. refrigerant gas will be generator. cooled down in the condenser, 4. The refrigerant vapour is condensed in refrigerant become a liquid. the condenser & the absorbent which 4. This refrigerant will be expanded by is coming from generator is cooled thermal expansion valve which is down in the absorber. The total cycle connected to evaporator. is operated under vacuum condition i.e.6 mm Hg
VAPOUR COMPRESSION MACHINES Types based on Compressors
• • • •
Reciprocating Compressor Centrifugal Compressors Screw Compressors and Scroll Compressors
Types • Steam Based • Double Effect Steam Fired Machines • Single Effect Steam Fired • Oil / Gas Based • Hot Water Based
STEAM BASED VAM Double Effect Steam Fired Machines : 3.5 kg / cm2 to 10 kg / cm2 • Steam pressure : 40 TR to 1400 TR TR • Capacity : 4.5 kg / hr @ 8 kg / cm2 / TR TR • Sp. Consumption
Single Effect Steam Fired : 4.5 kg / hr @ 8 kg / cm2 / TR TR • Sp. Consumption : 70 TR to 1400 TR TR • Capacity : 8.5 kg / hr @ 3 kg / cm2 / TR TR • Sp. Consumption
VAPOUR ABSORPTION MACHINES Oil / Gas Based VAM • Fuels : Kerosene, Diesel, LPG, LNG, Natural gas & Furnace Oil • Capacity : 30 TR to 770 TR TR Hot Water Fired VAM • Source : Hot Water (minimum of of 85 C) • Capacity : 30 TR to 650 TR TR °
DEVELOPMENTS IN THE FIELD OF VAM
• Split Evaporator for Improved Output and Coefficient of Performance (COP) • Drain Heat Exchangers for improved oil consumption Cupro--nic e in Con enser an A sor er • Cupro • Maintenance Friendly Design for Heat Exchangers • Leak Proof Service Valves • Vacuum Pump Improvement
SPLIT EVAPORATOR FOR IMPROVED OUTPUT AND COP
Conventional System • Lower Shell of VAM • Split into two sections • One each for Evaporator & Absorber Improved Design • - Split into three sections • - Evaporation section split into two • - One each on side of the Absorber
SPLIT EVAPORATOR FOR IMPROVEMENT OUTPUT
How ? • Improved Design • Allows uniform flow of the evaporated vapours • Optimal Absorption of refrigerant vapours by LiBr in the Absorber • Results in • Improvement in Evaporation rate • Enhanced Output
BENEFITS OF VAM Non--dependence on Electrical Power • Non • Environmentally Clean & friendly • Lesser Down Time • Lower Noise Level • Availability Step-less Modulation and • Continuous and Step-
• • • •
LIMITATIONS OF VAM Minimum chilled water Temperature possible : + 4.5 C Only water cooled condensers are available commercially. High initial investment °
APPLICATIONS OF VAM IN INDUSTRIES
• Automobile • Engineering • Petrochemicals • Pharmaceutical • Cement • Soft Drinks • Chemicals • Fertilizers • Refinery • Commercial Establishments and more
REFRIGERATION SYSTEM ENERGYCONSERVATION OPPORTUNITIES
• Replace Chiller (Usually Smaller) • Reduce Refrigeration Loads • Minimize Chiller Operation • Isolate S ecial Loads • Lower Condenser Water Temperature • Reasons to replace a chiller • Future Refrigerant Cost / Availability • Future Maintenance Repair Cost • Efficiency Improvements
REDUCTION IN REFRIGERATION LOAD
• The refrigeration load itself can be reduced by the following methods : • Reduction in the use of Refrigeration • Improved Insulation • e uc on n ux ary oa s REDUCTION IN USE OF REFRIGERATION
• Whether it is necessary? • If required, how much and what temperature?
IMPROVED INSULATION
• • • • • •
Insulation of Pipe Lines, Valves, Flanges etc. Better Design of Building and enclosures Provision of Films, Curtains, Venetian Blinds Orientation of Windows Provision of Natural Cooling and Lighting P anting o Trees
ENERGY CONSERVATION OPPORTUNIES ISOLATE SPECIAL LOADS
• Computer Room • Control Rooms • Office Administrative Building
ENERGY CONSERVATION OPPORTUNIES
• Optimize Cooling Tower Fan Energy • Raise Chilled Water Temperature • Optimize staging of Multiple Chillers • Eliminate bypass through dede-energized Chillers • Enhance Heat Transfer Surfaces for Efficiency Gains • Minimize Pump peration • Optimize Use of Cheap Rate Non Peak Hour Power • Using Cooling Tower Water if possible • Use Variable Speed for part load operation • Avoid Hot Gas bypass • Availability of Waster heat, low cost steam vapour absorption refrigeration.
ENERGY CONSERVATION OPPORTUNIES
• Temperature Drop between condensing and evaporator temperatures leads to power saving doubly • A unit operating at - 30 C uses more than twice . • Reduction in condenser water temperature by 1 C or raising Chilled Water Temperature by 1 C leads to 1 to 1.5 % saving in power consumption °
° °
EFFECT OF EVAPORATION TEMPERATURE Evaporation
Refrigeration
Compressor Shaft Power kW
kW / ton
5
67.58
55.3
0.81
0
56.07
52.3
0.94
.
.
.
- 10
37.20
46.6
1.25
- 20
23.12
38.7
1.67
-
MAINTENANCE ASPECTS IN REFRIGERATION • Remove Excess Charge •Clean the condenser periodically •Add refrigeration to correct load •Maintain oil temperature between 50 - 60 C °
ENERGY SAVINGS OPPORTUNITIES DISCUSSED IN DETAIL
• Efficient Scroll Compressors • Secondary Chilled Water Pump Opportunities • VSD used in Centrifugal Compressor • Ammonia VAR System • Cooling Tower Energy Optimization
SCROLL COMPRESSORS • The scroll compressor is the heart of the new
generation premium, high efficiency heat pumps and air conditioners. • Range Available : 5 TR TR - 15 TR • Scroll Compressors are finding acceptance in
• Principle of Working Two identical spirals or scrolls • One scroll remains stationery while the other orbits around the first • As this motion occurs, gas is drawn into the scrolls and • Moved in increasingly smaller pockets towards the center
WORKING OF SCROLL COMPRESSORS
• At this point, the gas now compressed to a high pressure is discharged from a part in the fixed scroll.
• compressed simultaneously, creating smooth, nearly continuous operation.
ENERGY EFFICIENCY OF SCROLL COMPRESSOR • 10 % more energy efficient than reciprocating • • • • • •
Compressors Near 100 % volumetric efficiency The scroll compression process occurs during a full 540 of rotation where 180 of rotation in rec proca ng compressors Results in : Smoother Compression & discharge The scroll design does not require a dynamic valve where piston Compressor needs. Suction & discharge process in a scroll compressor is physically separated. Results in : Lesser heat transfer, which improves overall efficiency. °
°
OPERATING PERFORMANCE
• Reliability - Fewer Moving Parts • Durability - Axial Axial and radial compliance make the scroll compressor more tolerant to liquid refrigerant and debris. • Lower Soun • Flooded starts normally will not harm scroll compressor
SECONDARY CHILLLED WATER SYSTEM ENERGY CONSERVATION OPPORTUNITIES
• Application - used for distribution of chilled water to the loads from the primary production loop. • Proposed System - VSD VSD for Sec. Chilled Water Pump
Case Study SECONDARY CHILLED WATER SYSTEM ECO
1
Power Consumption kW
Flow %
Hours %
Hours Run
30
5
438
23.33
40
5
438
50
10
60
1
2
4.73
10 219
2 072
23.56
6.08
10 319
2 663
876
24.03
8.01
21 050
7 017
10
876
24.71
10.61
21 646
9 294
70
10
876
25.62
14.04
22 443
12 299
80
20
1752
26.76
18.54
46 884
32 482
90
30
2628
28.17
24.28
74 031
63 808
100
10
876
30.22
31.48
26 473
27 576
100
8760
2 33 064
1 57 211
Two Way Valve Control
1
Energy Input kWh
2
2
VSD Control
• • •
SECONDARY CHILLED WATER SYSTEM ENERGY CONSERVATION OPPORTUNITIES Basis : 30 kW Pump Comparison with Two Way Valve Savings : 75 840 kWh VARIABLE SPEED DRIVE FOR CENTRIFUGAL COMPRESSOR
• Model Case Study • Chiller Plant Capacity • Power Consumption • • •
: :
Ref. SCREX 99 500 TR TR
at Full Load : 250 kW ( 0.5 kW / TR ) 82 % of total power consumption is by Chiller Motor in Chilled Water System. Constant speed chillers handle lower loads by gradually closing at set of guide vanes on the Compressor inlet while keeping the motor turning at full speed Closing the vanes create friction losses in Refrigerant flow, producting
RECOMMENDATION • Single stage compressors are especially well suited for Variable Speed Drive. • Power consumption can be reduced upto 30 % by installing VFD. 95065 kWh • Annual saving : LIMITATIONS • Multistage compressors have the added complexity of maintaining the appropriate inter stage pressure, hence varying the speed will upset this balance and this will penalise the performance of the compressor.
OTHER BENEFITS OF VSD
• Ideal soft starter (Inrush amp for VSD never exceeds the 100 % FLA of the motor where solid state starter of Star Delta starter have 300 - 400 % FLA). • Addition of VSD enhances the unloading capability of a Centrifugal chiller by varying the speed prior to closing the guide vanes. • Quite Operation • VSD also come with automatic power factor correction
VSD Vs CONSTANT SPEED OPERATING COST COMPARISON Load Poin ts
Tons
ECWT F
1
200
78
100
12 758
10 172
2 586
2
250
80
300
45 806
37 065
8 741
4
350
84
2 150
4 50 487
4 05 091
45 396
5
400
86
1 800
4 38420
4 12 744
25 676
6
450
88
200
56 709
55 754
955
7
500
90
100
32 438
33 851
-1 413
5 150 11 26 479
10 31 414
95 065
Total
°
Annual hours
•Alt 1 is for the chiller with constant speed unit •Alt 2 is for VSD chiller.
Annual kWh Alt 1
Alt 2
Savings
CASE STUDY ON HOT WATER FIRED VAPOUR ABSORPTION MACHINE • A continuous process industry in TN. • DG set details • Capacity : 2 Nos of 4 MW
• • Supply air @ 40 C • Design parameter is at 25 C • Average Units generation • (per DG set) : °
°
3400 kW / hr
RECOMMENDATIONS • One number of Vapour Absorption Machine (VAM) • • • • • • • • •
connected to one DG set hot water circuit with a provision to link the second DG set, in case the first is under maintenance. Capacity of VAM : 173 TR Chilled water flow : 104.6 m3 hr Chilled water inlet / outlet temp. : 12 / 17 C Hot water flow : 144 m3 / hr Hot water inlet / outlet temp : 91 / 85 C Cooling Water Flow : 300 m3 / hr Cooling water inlet / outlet temp : 32 / 36.5 C Power consumption for VAHP : 3.7 kW Charge air cooling requirement : 73 TR °
°
°
SAVINGS IN FUEL CONSUMPTION BY VAM
• Savings in specific fuel consumption / kW • • • • •
6.5 gm / kW Savings in fuel cost / year : Rs. 39 lakhs Savings due to additional loading in DG :Rs. 50 lakhs. otal savin s : Rs. 89 lakhs Other benefit : 100 TR of chilled water for plant use (OR) 173 TR of Chilled Water Investment of Rs. 44 lakhs
AMMONIA VAPOUR ABSORPTION REFRIGERATION (AVAR) - FEATURES
• Ability to operate at rates higher than nameplate capacitors without negative consequences. Inertial storage at low loads to meet transient with sizable spikes. • Putting up with interrupted heat supply while maintaining cold supply on continuous mode. Low pressure steam and available waste heat sources can be utilized.
FACTORS IN FAVOUR OF AVAR
• Increase in cost of electricity and low cost steam generation through various available resources. • Improvement in COP (COP has gone up from 0.4 to 0.56, in latest machines) Example • COP • Evaporation temp • Heating media temp • Basis
: : : :
0.56 - 30 C 172 C Cooling Water at 33 C °
°
°
BARRIERS IN AVAR
• Premium first cost • Lack of familiarity • maintenance problem • Poorer COP (even though heat energy price compared to electricity is low) • Ineffective or nonexistent sales structure for commercial implementation after R & D.
BENEFITS OF AVAR OVER VCR Basis • Cooling Water at 33 C • Evaporation Temperature at 20 C • Unit TR Requirement °
°
. : Rs 500 / MT
• Steam Cost • AVAR System Requirements • Steam Quantity Requirement : 9 kg • Power Consumption : 0.25 kWh : Rs 5.5 / TR • Total Cost
AVAR OPERATING BENEFITS • • • •
Compression Refrigeration Requirements : Power Consumption : Operating Cost : Difference in operating Cost :
1.75 kWh Rs 7.0 / TR TR Rs 1.5 / TR TR
COOLING TOWER TOWER - FANS APPLICATION • Cooling Towers are used to cool condenser water in water cooled Chiller Systems. • Water cooled chiller systems provide 20 % more efficient cooling system than air cooled chiller systems. • Conventional Control Systems • ON / OFF Control • Two Speed Motors • Adjustable Pitch Blade Fans
COOLING TOWER TOWER - CASE STUDY Case Study on Cooling Tower fan with VSD Drive. •Basis : 30 kW fan •Comparison with two speed motor is made •Savings : 83 588 kWh BENEFITS OF VSD CONTROL OVER TWO SPEED MOTOR CONTROL Flow
%
1
Hours
%
Hours Run
Energy Input kWh
Power Consumption kW
1
2
.
.
1
2
50
15
1314
12.80
4.83
16 819
6 347
60
35
3066
12.80
7.85
39 245
24 068
70
20
1752
30.00
11.93
52 560
20 901
80
15
1314
30.00
17.27
39 420
22 693
90
10
876
30.00
24.16
26 280
21 164
100
0
0
0
0.00
0
0
100
8760
1 79 930
96 342
Two Way Valve Control
2
VSD Control
