air conditioning with solar energy

7/27/2019 Air Conditioning With Solar Energy

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FraunhoferInstitutSolare Energiesysteme

page 1barcelona_english

SERVITEC

Barcelona, Oct ober 3, 2000

Air Conditioning with Solar Energy

Dr. Hans-Martin Henning

Fraunhofer-Institut fr Solare Energiesysteme ISE, Freiburg


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1 Fundamentals1.1 Thermodynamics1.2 Climatic conditions

1.3 Definition of air conditioning2 Systems & Components2.1 Chillers

2.2.1 Absorption chillers2.2.2 Adsorption chillers2.2 Open cycles - desiccant cooling2.3 Solar collectors3 Solar air conditioning systems

3.1 Comparative study of solar assisted systems3.1.1 Compared systems

3.1.2 Required collector area3.1.3 Primary energy saving

3.1.4 Pay back time3.2 Autonomous systems4 Built examples

5 Summary & outlook

Contents

F


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photovoltaic-

peltier-system

photovoltaik-

compression

system

electricsystems

solid sorbents

(rotary wheels,

fix bed process)

liquid

sorbents

opencycles

liquid

sorbents

adsorption chemical

reaction

solid

sorbents

closedcycles

heat transformation

systems

rankine-process/compression

Veulleumier-cycle

thermomechanical

processes

thermal drivensystems

solar cooling

processes

Fundamental

Solar cooling processes


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Thermal

driven coolingprocess

heat

chilledwater

conditionedair

Fundamental

Solar thermal air conditioning systems


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Fundamental

mechanicalpower P

driving heatTheat

waste heatTwaste

cooling powerTcold

heatengine

vapourcompressionmachine

wasteheat

T

waste

driving heatTheat

cooling powerTcold

thermal drivencooling machine

wasteheat

Twaste

Thermodynamic process


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60 80 100 120 140 160 180 200

driving temperature[C]

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5reversible COP [-]

evaporator temperature

0C 5C 10C 15C

maximum COP of coolingmachines

Fundamental

COP (Coefficient ofPerformance) =

produced cold___required driving heat


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35 50 65 80 95 110 125 140 155 170 185 200 215 230 245

fluid average temperature [C]

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1 collector efficiency [-]radiation

200 W/m^2

400 W/m^2

600 W/m^2

800 W/m^2

1000 W/m^2

tpyical solar collectorefficiency curves

Fundamental


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maximum COP of coolingmachines

Fundamental

35 55 75 95 115 135 155 175 195 215 235

driving temperature [C]

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1collector efficiency, COPsol [-]

0

0,3

0,6

0,9

1,2

1,5

1,8

2,1

2,4

2,7

3COP [-]

collector

efficiency

COPsol

COP

COPsol =

COP * collector


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35 50 65 80 95 110 125 140 155 170 185 200 215 230 245

fluid average temperature[C]

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7COPsol [-]

radiation200 W/m^2

400 W/m^2

600 W/m^2

800 W/m^2

1000 W/m^2

COPsol for differentcollector radiation values

Fundamental


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200 300 400 500 600 700 800 900 1000

radiation [W/m^2]

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7COPsol [-]

65

80

95

110

125

140

155

170temperature [C]

maximum COPsol andrespective temperatureas function of radiationon collector

Fundamental


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definition of airconditioning

Fundamental

n air conditioning: control of indoor airtemperature and humidity according tocomfort demands

n main loads are:

conditioning of ventilation air (supplyof fresh air)

sensible internal loads: persons,equipment, artificial lighting

latent internal loads: persons, plants,others (e.g. kitchen)

solar loads (windows, glazings)

conduction loads (walls, windows)

conditioning of

ventilation air

solar

loads

internal

loads

supplyair

return

air


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specific cooling load ofconditioning ofventilation air inkWh per m3/h per year

supply air temperature:18C

supply air humidity:8 g/kg

requirements forconditioning of ventilationair at different sites

Fundamental

Copenhagen Freiburg Trapani Bangkok0

10

2030

40

50

60

70

8090

100cooling load of ventilation air

sensiblelatent

total

sensible 0,57 1,95 5,93 28,48

latent 1,43 2,88 17,59 69,33

total 2 4,84 23,52 97,81


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1 Fundamentals1.1 Thermodynamics

1.2 Climatic conditions1.3 Definition of air conditioning

2 Systems & Components2.1 Chillers

2.2.1 Absorption chillers2.2.2 Adsorption chillers2.2 Open cycles - desiccant cooling2.3 Solar collectors3 Solar air conditioning systems



3.1.4 Pay back time3.2 Autonomous systems4 Built examples5 Summary & outlook

Contents

F


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method closed cycle open cyclerefrigerant cycle closed refrigerant cycle refrigerant (water) is in contact to the

atmosphereprinciple chilled water dehumidification of air and evaporative

cooling

phase of sorbent solid liquid solid liquid

typical materialpairs

water - silica gel,ammonia - salt 1

water - water/lithiumbromide,

ammonia/water

water - silica gel,water -

lithiumchloride

water - calciumchloride, water -

lithium chloridemarket availabletechnology

adsorption chiller absorption chiller desiccant cooling -

typical coolingcapacity [kW cold]

adsorption chiller:50-430 kW

absorption chiller:20 kW - 5 MW

20 kW - 350 kW(per Module)

-

typical COP 0.3-0.7 0.6-0.75 (singleeffect))

0.5->1 >1

driving temperature 60-90C 80-110C 45-95C 45-70Csolar collectors vacuum tubes, flat

plate collectorsvacuum tubes flat plate collectors,

solar air collectorsflat plate collectors,solar air collectors

1) still under development

Systems & Components

processoverview

S &C


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systemoverview

backupheater

chiller

heat supply system chilled water

conditioned airbuilding/room

returnair

supplyair ambientair

exhaustair

bufferstorage

desiccant

wheel

heatreco

very

wheel

S t &C t


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liquid

refrig

eran

t

lowconcentra

tion

high

concentratio

n

.Q

C

.Q

G

.Q

A

.Q

Ev

single-effectabsorption cycle(e.g. water -lithiumbromide)


S stems&Components


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n absorption chillers are market availablecomponents, mainly employed in combined heat-

power-cold systemsn chilled water can be used for conditioning of air

(dehumidification, temperature decrease) or for coldsupply in the rooms (fan coils, chilled ceilings,...)

n many products available in the high capacity range(tpyically > 200 kW); only few products with small

capacitiesn driving temperature of single effect machines at

> 85C with COP of 0.6-0.7

n driving temperature of double-effect machines at> 150C with COP of 1.2

status of absorptionchillers


Systems&Components


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adsorption chiller cycle


adsor-

ber 1

adsor-

ber 2

condenser

evaporator

adsor-

ber 1

adsor-

ber 2

condenser

evaporator

condenser

evaporator

adsor-

ber 2

adsor-

ber 1

condenser

evaporator

adsor-ber 2

adsor-ber 1

phase 1

phase 2

phase 3

phase 4

Systems&Components


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status of adsorptionchillers


n adsorption chillers are market available from

to Japanese companiesn chilled water can be used for conditioning of

air (dehumidification, temperature decrease)or for cold supply in the rooms (fan coils,chilled ceilings,...)

ncooling capacity range 70 kW - 400 kW

n driving temperature starting at 55C

n COP at design conditions 0.65

Systems&Components


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principles of opencooling cycles (desiccantcooling cycles)


n open cooling cycles use the effect of

evaporative cooling

n production of conditioned air (no chilledwater)

n potential for application of evaporativecooling is increased by dehumidification of

fresh air

n thermal energy required for regeneration ofthe sorbent (desiccant)

n separation of cooling and conditioning ofventilation air

Systems&Components


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status of desiccantcooling systems


n system components and complete systemsmarket available and employed since many

years

n about 5 producers of wheels worldwide(Japan, US, Sweden, Germany)

n driving temperatures for regeneration usabledown to about 45C

n technology raised attention due to CFC-problem during past 10 years

n adiabatic dehumidificationprocess

Systems&Components


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bypass

humidifiers

supplyair

returnair

dehumidifier heat recovery

1 2 3 4 5 6

78

10

11

heat heat

9

freshair

exhaustair

standard desiccantcooling cycle


6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

humidity ratio [g/kg]

1015202530354045505560657075

temperature [C]

1

2

35

67

8

9

10

11

10 %

20 %

30 %

40 %50 %

70 %

100 %

Systems&Components


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5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35humidity ratio [g/kg]

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75temperature [C]

1

2

3

56

7

8

9

10

11

10 %

20 %

30 %

40 %

50 %

70 %

100 %

4

bypass

humidifier

supplyair

returnair


heat

freshair

exhaustair

chilled

water

chilled

water

1 2 3 4 5 6

7811 910

desiccant coolingcycle for humidclimates




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WINDOWS design tool

y p


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20 m2 Flachkollektoren (GreenOneTec/Sonnenkraft)

20 m2 Solarluftkollektoren (Grammer)

2,0 m3 Pufferspeicher (Solvis)

Vermessung von Sorptionsrdern

vielfltige Verschaltungsvarianten

Entwicklung & Optimierung von Regelungsstrategien

begleitende Systemsimulationen



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modelling of sorptiondehumidifier

y p

0 1 2 3 4 5 6 7 8 9 10

calculated dehumidification [g/kg]

0

1

2

3

4

5

6

7

8

9

10measured dehumidification [g/kg]

1980 m3/h

2790 m3/h

3670 m3/h

manufacturer



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solar collectors forthermal driven cooling

25 50 75 100 125 150 175

fluid average temperature [C]

0

0,2

0,4

0,6

0,8

1collector efficiency [-]

flat plate collector

evacuated tube collectorsolar air collector

desiccantcooling

adsorption

single effectabsorption

double effect

absorption

ambient temperature25C

collector radiation800 W/m2


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2.2.1 Absorption chillers2.2.2 Adsorption chillers2.2 Open cycles - desiccant cooling

2.3 Solar collectors

3 Solar air conditioning systems



3.1.4 Pay back time3.2 Autonomous systems4 Built examples5 Summary & outlook

Contents

F

Solar air conditioning system


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solar assistedsystems

n solar collector system covers a

certain fraction of regeneration

heat

n obtainable indoor air conditionsnot limited by solar gains

n system design: solar fraction

solar autonomoussystems

n solar collector system deliversregenaration heat completely

n obtainable indoor air conditionslimited by available solar energy

n system design: probability function ofindoor air temperature and humidity

Air conditioning withsolar energy



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BuildingSimulation

(TRNSYS)

buildingdata

meteorologicaldata

simulation ofAC system

(CONVCOOL,SGKCOOL)

simulation ofsolar system(SOLCOOL)

cooling /heating loadtime series

driving energy

time series

economicanalysis(EXCEL)

solar fractionfor cooling/

heating

energy

balance,costs

study on solar assisted airconditioning



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climatic and load dataparameter Copenhagen Freiburg Trapani

latitude [ north] 55.8 48.0 37.9

annual average temperature [C] 8.09 10.42 17.53

annual average rel. humidity [%] 82.92 73.36 76.32

annual average humidity ratio [g/kg] 5.81 6.04 9.99

annual radiation sum on collector [kWh/m2] 1127.3 1195.7 1919.5

annual average cooling load [W/m2] 42.8 52.7 108.9

Jan Feb Mar Apr May Jun Jul Aug Sept Okt Nov Dec

0

3

6

9

12

15

18cooling load [kWh/m 2]

Copenhagen

Freiburg

Trapani



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building

indoor conditions

investion costs

energy costs

climatic data

reference office building with south orientedglazed facades (glazing fraction about 60 %), floorarea 400 m2

according to german standard DIN 1946/II

10 % of investion costs

according to values on german market (1998)(electricity: 0.08 US$/kWh, 171 US$/kWpeakgas: 0.023 US$/kWh, 4.5 US$/kWpeak)

Copenhagen/Denmark, Freiburg/Germany,Trapani/Sicila

assumptions for the comparative study


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heat recoveryCCh = compression chillerHT = heater (gas burner)

cooling

loads

cold, dry

warm, humid

CCh HT

reference system with adiabatic cooling in return air


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CT

heat recovery

CT = cooling towerAbCh = abs. chiller

AdCh = ads. chillerHF = humidifier

coolingloads

cold, dry

warm, humid

AbChAdCh

aux.heater

HF

system with thermal driven chillers



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humidifierscoolingloads

cool,dry

auxiliaryheater

warm,humid


1 2 3 4 5 6

7891011

solar assisted desiccant cooling system (Copenhagen, Freiburg)

l i d



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humidifiers

desiccantwheel

heat recovery

cooling

loadscold,dry

warm,humid

auxiliaryheat

VPCCTVPC = vapour compr. chillerCT = cooling tower

solar assisteddesiccant coolingsystem (Trapani)


d fi iti


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definitions

solar fraction forcooling (SFC)

specific collectorarea (m2/m2)

fraction of the total heat required for cooling (airconditioning) which is supplied by the solar system

collector (absorber) area per floor area ofconditioned space


d t


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compared systems

ABV

ADV

ADF

DCF

DCSA

absorption chiller system with evacuated tube

collector

adsorption chiller system with evacuated tubecollector

adsorption chiller system with selective flat plate

collector

desiccant cooling system with selective flat platecollector

desiccant cooling system with solar air collector


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primaryenergybalance


normalized primary energy demand [%] FREIBURG


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primary energy balance

ABV ADV ADF DCF DCSA0

25

50

75

100

125

150

175

200normalized primary energy demand [%]

solar fraction cooling

0 0,3 0,5 0,7 0,85

COPENHAGEN

reference


25

50

75

100

125

150

175



0 0,3 0,5 0,7 0,85

FREIBURG

reference


25

50

75

100

125

150

175



0 0,3 0,5 0,7 0,85

TRAPANI

reference

electricpeakloaddueto



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electric peak load due toair conditioning

absorption/adsorption desiccant cooling0

25

50

75

100normalized maximum electric power [%]

Copenhagen Freiburg Trapani100 % = reference system

simplepaybacktime


80simple payback time [a] TRAPANI


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simple pay back time


10

20

30

40

50

60

70

80simple payback time [a]


0 0,3 0,5 0,7 0,85

COPENHAGEN


10

20

30

40

50

60

70

80simple payback time [a]


0 0,3 0,5 0,7 0,85

FREIBURG


10

20

30

40

50

60

70

80solar fraction cooling

0 0,3 0,5 0,7 0,85

Solarautonomousdesiccantcoolingsystemsemployingsolarair



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Solar autonomous desiccant cooling systems employing solar aircollectors

system integrated collector regeneration with ambient air

desiccantwheel

heat recovery

wheel

coolin

loadscold,dry

warm,humid

humidifier

humidifiercooling

loads

cold, dry

warm, humid

desiccantwheel

heat recovery

wheel

results fora lectureroominFreiburg



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0

5

10

15

20

25

30

35

40

0 0,005 0,01 0,015 0,02 0,025

Feuchtegehalt X [ kg/kg ]

Temperatur[C]

T_operativ

T_luft

DIN 1946 T2

= 1,0

= 0,7

= 0,6 = 0,5 = 0,3 = 0,4

0

5

10

15

20

25

30

35

40

0 0,005 0,01 0,015 0,02 0,025

Feuchtegehalt X [ kg/kg ]

T

emperatur[C]

T_operativ

T_luft

DIN 1946 T2

= 1,0

= 0,7

= 0,6 = 0,5 = 0,3 = 0,4

results for a lecture room in Freiburg

specific collector area 0.22 m2 per m2 of room area

n operative room temperaturen room air temperaturenDIN 1946 part 2

Contents


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2.3 Solar collectors3 Solar air conditioning systems

3.1 Comparative study of solar assisted systems

3.1.1 Compared systems3.1.2 Required collector area3.1.3 Primary energy saving

3.1.4 Pay back time3.2 Autonomous systems

4 Built examples5 Summary & outlook

Contents

F

built example

solarassisteddesiccantcooling systeminSintra /Portugal


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solar assisted desiccant cooling system in Sintra / Portugal

n air conditioning of theoffice from companyATECNIC

n desiccant system fromrobatherm

n solar collector fromSETSOL/Portugal

n commissioned Dec. 99

n funded by the EU(THERMIE-program)

n coordination andscientific evaluation:

Fraunhofer ISE

INETI / Lissabon

desiccantcoolingmachine inSintra /Portugal (manufacturer:

built example


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desiccant cooling machine in Sintra / Portugal (manufacturer:robatherm)

technical data of the systemin Sintra / Portugal

built example


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technical data of the system in Sintra / Portugal

DEC system: variable volume flow system with nozzle type air humidifiers in supplyand return air, heat recovery wheel and desiccant wheel (silica gel), bypass alongdesiccant wheel in supply air stream and bypass along regeneration air heatexchanger and desiccant wheel

maximaum air volume flow 9600 m3/h

maximum cooling power 75 kW

maximum electric load 15 kW

COP at design conditions(cooling capacity/regenerationheat)

0.78

solar collector system: CPC-collector with low optical concentration ratio (CPC =compound parabolic concentrator) filled with anti-freezing fluid; connected tobuffer storage (water) with plate heat exchanger

buffer storage volume 3 m3

collector area 72 m2

expected solar fraction for cooling(regeneration heat)

70 %

expected solar fraction for heating 70 %

solar assisted air conditioning of a laboratory building in

built example


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g y gFreiburg (university hospital) with adsorption cooling technology

schematic of the

built example


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system in Freiburg

Contents


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2.3 Solar collectors3 Solar air conditioning systems

3.1 Comparative study of solar assisted systems

3.1.1 Compared systems3.1.2 Required collector area3.1.3 Primary energy saving

3.1.4 Pay back time3.2 Autonomous systems4 Built examples

5 Summary & outlookF

general results

summary & outloo


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g

0.2-0.4 m2

per m2

of floor area of conditioned spac for asolar fraction of 70-80 %

70-80 % required in order to achieve relevant primaryenergy saving

possible if the user does not request strict indoor air

conditions (solar comfort improvement)

system design required which takes specific climaticconditions into consideration

typcial value of requiredcollector area (office)

required solar fraction withsolar assisted systems

solar autonomous systems

system design

general results (continued)

summary & outloo


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n evacuated tube collectors for absorptions systemsand adsorption systems

n flat plat collectors for desiccant cooling systems andeventually adsorption

n solar air collectors for desiccant cooling (e.g.autonomous systems)

collector technology

economic feasibility n payback time depends on technology and climate

n lowest pay back time found for desiccant cooling inTrapani (with conventional chiller backup) (less than10 years)

n payback time in general in the same range as forsolar domestic hot water systems or below

lessons learned from pilot systems

summary & outloo


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n solar heat source is not constant (time dependance

of power and temperature)n system control is more complex than for systems

with standard heating system (gas or oil burner)

n optimized control has a strong influence on systemperformance

control issues

no standardized system design guidelines or toolsavailable

important to control operation in order to identifymistakes in control and/or design

system design

operation experiences

To emp loy solar act ive equipm ent makes on ly sense ifneeds for an

summary & outloo


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To emp loy solar act ive equipm ent makes on ly sense if

pot entials of energy saving and reduction of coo l ing

loads have been explo it ed

Building

n reduction of internal loads (equipm., lighting)

n advanced shading & daylighting concepts

n reduction of conduction loads

n reduction of leakages

A/C system

n separation of ventilation (handling of latentloads) and cooling (handling of sensible loads)

n employing heat (or enthalpy) recovery systems

n employing high efficiency chillers

integrad approach


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air conditioning with solar energy

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