Exergy Analysis eof Solar Air.pdf

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    ACTION COST 23 ACTION COST 23 11

    Exergy Analysis of Solar Air-ConditioningSystems and their Applicability

    Presentation at the C23 Conference, WP1, September 24 2008, Munich

    Christopher J. KoroneosEvanthia A. Nanaki

    George A. Xydis

    Strategies for a Low Carbon Built Environment

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    The exergy concept

    Exergy is defined as the property of the system, whichgives the maximum power when it is brought to athermodynamic equilibrium state. It is the maximumavailable energy.

    Ex = ?H - T ?SExergy Analysis & Solar Cooling Systems: Analysis andDesign of Innovative Systems in the Built Environment. A Alowlow -- exergy heating or cooling system was defined by IEAexergy heating or cooling system was defined by IEA

    Annex 37 as a system that allows the use of low valued Annex 37 as a system that allows the use of low valuedenergy as a source. Theenergy as a source. The greatest exploitation of solarcooling potential is achieved in buildings with high thermalgains during the day and consequently high cooling load .

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    Cooling energy consumptionCooling energy consumption

    During the last few decades energy consumption for cooling hasDuring the last few decades energy consumption for cooling hasincreased dramatically in most European countriesincreased dramatically in most European countries

    During the summer months the demand for electricity in GreeceDuring the summer months the demand for electricity in Greeceincreases (extensive use of heating ventilation and air conditioincreases (extensive use of heating ventilation and air conditio ningning

    systemssystems increasesincreases peak electric loadpeak electric load causing major problems incausing major problems inthe electric supply)the electric supply)

    In the current practice, air conditioning is exclusively based iIn the current practice, air conditioning is exclusively based i n the usen the useof electric energy, while the use of solar energy is limited toof electric energy, while the use of solar energy is limited to heating ofheating ofdomestic hot water, and in limited applications for space heatindomestic hot water, and in limited applications for space heatin g andg andfewer for cooling.fewer for cooling.

    It has been estimated that the total electric energy consumptionIt has been estimated that the total electric energy consumption ininGreece, in 2003, for central air conditioning systems was 2909Greece, in 2003, for central air conditioning systems was 2909 GWh/yGWh/y ,,whereas the per capita consumption of electricity was estimatedwhereas the per capita consumption of electricity was estimated at 371at 371KWh/ yKWh/ y

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    Solar Collectors in Greece

    Sales & Energy production of solar collectors in Greece

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    95% of the collector area installed up today : households264 m 2 / 1,000 inhabitants

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    Solar Cooling System

    Cooling tower

    Generator Condenser

    Expansion valve

    Evaporator

    Solution heat exchanger

    Absorption

    L i B r

    LiBr/H 2O

    Refrigerantliquid

    Refrigerantliquid

    Refrigerantsteams

    Refrigerantsteams

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    Exergy AnalysisExergy balance of the systemExergy balance of the system ?? XinXin == ?? XlostXlost ++?? XoutXout

    (kW)(kW)Exergy efficiency of the system

    n = ? Xout / ? Xin = 1 ? Xlost / ? XinTotal exergy input into the absorption refrigeration cycle, in each component:

    Xin,total = Xin,g + Xin,c + Xin,exv + Xin,e + Xin,a+ Xin,she

    Total exergy output of the absorption refrigeration cycle :

    Xlost,total = Xlost,g + Xlost,c + Xlost,exv + Xlost,e + Xlost,a +Xlost,she

    g=Generator,c=Condenser, exv=Expansion Valve, e=Evaporator, a=Absorber,she=Solution Heat Exchanger

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    Exergy Analysis

    The conditions used are the following: Ambient temperature of ?0 = 25 C,Heat exchanger efficiency e= 0.5,Temperature of cold water ?17 = 16 ?C,Temperature of cold water ?18 = 10 ?C,Temperature of hot water ?11 = 100 ?C,Mass rate of flow m7 = 0,005 kg/s

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    SHEGenerator

    Condenser Expansion

    Valve Evaporator Absorber

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    Ein (kW) Elost (kW)

    Exergy efficiency of thdifferent solar thermalsystems components

    xergy inputs andergy losses at

    ifferent solar thermalstems components

    0.000.100.200.300.40

    0.50

    0.600.700.800.901.00n

    SHE Generator Condenser ExpansionValve

    Evaporator Absorber

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    Application of solar cooling system inGreece: the case study of Igoumenitsa

    A medical center located near A medical center located near IgoumenitsaIgoumenitsa -- a city in northa city in north --westernwesternGreece with average rainfall of 1,100mm/ year Greece with average rainfall of 1,100mm/ year -- having units for thehaving units for thetreatment of patients, offices, labs and auxiliary spaces.treatment of patients, offices, labs and auxiliary spaces.The building was designed in 1984 and consists of a ground floor The building was designed in 1984 and consists of a ground floor area of 1,240marea of 1,240m 2

    and height of 3.60 m and a basement area of 600mand height of 3.60 m and a basement area of 600m 2 and height of 2.8 m.and height of 2.8 m.

    The structural components of the building consist of:The structural components of the building consist of: double casing external walls with insulation 4cm, K= 0.55 kcal/double casing external walls with insulation 4cm, K= 0.55 kcal/ mm 22 00 CC internal walls : 10cm, K= 1.5 kcal/ minternal walls : 10cm, K= 1.5 kcal/ m 22 00 CC insulated roof, K= 0,47 kcal/ minsulated roof, K= 0,47 kcal/ m 22 00CC marble insulated floor 5cm, K= 0.52kcal/ mmarble insulated floor 5cm, K= 0.52kcal/ m 22 00 CC aluminum window frames, K= 0.52kcal/ maluminum window frames, K= 0.52kcal/ m 22 00 CC sunlight protection of the building consisting of opensunlight protection of the building consisting of open --colored walls and internalcolored walls and internal

    curtaincurtain

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    Cooling LoadsThe calculation of the buildingThe calculation of the building s cooling loads took into consideration the following:s cooling loads took into consideration the following:

    internal temperature 26internal temperature 26 ooCC internal humid 50%internal humid 50% climatic data for the city ofclimatic data for the city of IgoumenitsaIgoumenitsa calculation method : Carriercalculation method : Carrier checking times: 08:00checking times: 08:00 18:0018:00

    reporting months: 5 (Mayreporting months: 5 (May -- September)September)

    KWatt

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    34

    8p

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    9p

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    11p

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    12p

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    68

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    68am 9am 10am 11am 12 pm 1pm 2pm 3pm 4pm 5pm 6p

    Cooling loads of July 2006

    Di i i h

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    Dimensioning o the ystemChillerChiller ((YazakiYazaki type WFCtype WFC --20)20) Cooling capacity: 20RT (70kW, 240,000Btu/h)Cooling capacity: 20RT (70kW, 240,000Btu/h) COP: 0.7COP: 0.7

    Temperature of water: 9Temperature of water: 900

    CC Temperature of water at the generator: 75Temperature of water at the generator: 75 -- 100100 00CC Nominal operating temperature :88Nominal operating temperature :88 00CC Temperature of water at the condenser: 29.5Temperature of water at the condenser: 29.5 00CCCooling tower (wet type) Cool ing tower (wet type) Capacity : 70kWCapacity : 70kW Rate of air flow: 130Rate of air flow: 130 --170 m3/h per kW of cooling capacity170 m3/h per kW of cooling capacity Electrical consumption: 6Electrical consumption: 6 --10 W per kW of cooling capacity for axial fans and 1010 W per kW of cooling capacity for axial fans and 10 --20 W per kW of20 W per kW of

    cooling load for radial fans.cooling load for radial fans.Solar thermal collector field (flat plate co llector)Solar thermal collector field (flat plate co llector) Collector Collector s