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Optimization in Refrigeration Systems
P.L.DharI.I.T. Delhi
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Synopsis
The design ProcessNeed for OptimizationHow Energy Conservation – innovative concepts
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The Design Process
Traditional approachDesign of a window air-conditioner
What is the basis of choosing ?Condenser TemperatureEvaporator temperatureNo. of RowsTube diameter
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The Design ProcessCondenser temp
Condenser size Compressor Power Consumption
Evaporator Tube Dia
Surface Area / frontal area
Heat transfer coefficient
Pressure gradient
? ?Effective temp difference?
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Why Optimization ?
Increasing CompetitionIncreasing energy costsStringent energy standardsEcological considerations
Availability of computational tools
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Formulation of an Optimization Problem
Three basic steps :Objective functionVariablesConstraints
Special features of thermal system Optimization
Nature of variables—discrete + continuousWe may want to optimize only some equipment NOT the whole system
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Optimum Design of a Refrigeration System -- problem formulation
Min TCs = FCe + FCc + RCe + RCc +Rcco
TCs= ΣNte(i) Lte Cct +Σ Ntc(i) Ltc Cct + [K Mwe PDe + K Mwc PDc + 0.746 (BHP) ] Ckw Lh
Variables : Lte , Nte( 1,2) ; Ltc , Ntc (1,7)No of passes, Fin design, tube layout, etc
Constraints: :Qe = Qer ; Mwe = Mwer, Twic = Twicr ; Qc = Qcr
Max Vel of water < Vr; Tube lengths within bounds
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Optimizing a ComponentCase Study 40 TR DX Chiller
Min. initial cost design
SN No of tubes shell dia baffle Obj fn pr. atcut entry psi
1 12 16 20 24 30 32 32 32 34
1.28 .24 1452 77.5
2 16 16 17 21 1.07 .324 998 78.7
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Optimizing a ComponentCase Study: Condenser coil of an AC
Min initial cost design
Design variable
Initial Design
Optimized Design
No of Rows 2 2No of Ckts 2 3Tube Length .585 m .594 mTube O/ D 7 mm 7 mmTubes/row 23 21Heat Transfer 5080 W 5090 WPressure Drop 1.0166 bar .8438 barBase Cost Rs 6377 Rs 5940
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ECO – Design of Refrigeration Equipment
Life cycle analysis based on emissions
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Reducing Energy Consumption
What should be the thermostat settings of a Window AC ?Do we need to maintain 24oC indoors ?Experience of Air conditioned trains .Comfort research shows PPD for 24oC is the same as for 27.2oC. Impact of high outdoor temperatures and short duration of occupancy on “optimal” indoor temperatures
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Reduce Energy Consumption through Innovative Concepts
Using stratification to reduce cooling loadWindow AC + Table fan
Regenerative evaporative cooling for “hot-dry” climates : “Green AC”Regenerative Evaporative cooling based cool chests for vegetable & fruit retail outlets
Desiccant based cooling
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Reduce Energy Consumption through innovative concepts
Combining multiple uses -- Customized A/C Solutions e.g. for kitchens, hostels, restaurants
Air conditioning, cold water, hot waterMultiple indoor and outdoor unit split ACFuzzy Control + variable speed control for energy savingVariable dead-band thermostatsPersonal AC
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Reduce Energy Consumption through innovative concepts
LPG based AC / refrigeratorBio-mass/Bio-gas energized cold chests for rural areasLow cost Domestic refrigerator without freezer
Consumer education
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Thank you !