Optimization in Refrigeration Systems

P.L.DharI.I.T. Delhi

Synopsis

The design ProcessNeed for OptimizationHow Energy Conservation – innovative concepts

The Design Process

Traditional approachDesign of a window air-conditioner

What is the basis of choosing ?Condenser TemperatureEvaporator temperatureNo. of RowsTube diameter

The Design ProcessCondenser temp

Condenser size Compressor Power Consumption

Evaporator Tube Dia

Surface Area / frontal area

Heat transfer coefficient

Pressure gradient

? ?Effective temp difference?

Why Optimization ?

Increasing CompetitionIncreasing energy costsStringent energy standardsEcological considerations

Availability of computational tools

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

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

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

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

ECO – Design of Refrigeration Equipment

Life cycle analysis based on emissions

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

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

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

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

Thank you !