air conditioning with solar energy - eduvinet · 1.3 definition of air conditioning 2 systems &...

Fraunhofer InstitutSolare Energiesysteme

page 1barcelona_english

SERVITECBarcelona, October 3, 2000

Air Conditioning with Solar Energy

Dr. Hans-Martin HenningFraunhofer-Institut für Solare Energiesysteme ISE, Freiburg



1 Fundamentals1.1 Thermodynamics1.2 Climatic conditions1.3 Definition of air conditioning2 Systems & Components2.1 Chillers2.2.1 Absorption chillers2.2.2 Adsorption chillers2.2 Open cycles - desiccant cooling2.3 Solar collectors3 Solar air conditioning systems3.1 Comparative study of solar assisted systems3.1.1 Compared systems3.1.2 Required collector area3.1.3 Primary energy saving3.1.4 Pay back time3.2 Autonomous systems4 Built examples5 Summary & outlook

Contents

F



photovoltaic-peltier-system

photovoltaik-compressionsystem

electricsystems

solid sorbents(rotary wheels,fix bed process)

liquidsorbents

opencycles

liquidsorbents

adsorption chemicalreaction

solidsorbents

closedcycles

heat transformationsystems

rankine-process/compression

Veulleumier-cycle

thermomechanicalprocesses

thermal drivensystems

solar coolingprocesses

Fundamentals

Solar cooling processes



Thermal driven cooling process

heat

chilled water

conditioned air

Fundamentals

Solar thermal air conditioning systems



Fundamentals

mechanicalpower P

driving heatTheat

waste heatTwaste

cooling powerTcold

heatengine

vapour compression machine

wasteheat

Twaste

driving heatTheat

cooling powerTcold

thermal driven cooling machine

wasteheat

Twaste

Thermodynamic process



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 temperature0°C 5°C 10°C 15°C

maximum COP of coolingmachines

Fundamentals

COP (Coefficient ofPerformance) =

produced cold___required driving heat



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

1collector efficiency [-]

radiation200 W/m^2400 W/m^2600 W/m^2800 W/m^21000 W/m^2

tpyical solar collectorefficiency curves

Fundamentals



maximum COP of coolingmachines

Fundamentals

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 [-]

collectorefficiency

COPsol

COP

COPsol =

COP * ηcollector



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^2400 W/m^2600 W/m^2800 W/m^21000 W/m^2

COPsol for differentcollector radiation values

Fundamentals



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

Fundamentals



definition of airconditioning

Fundamentals

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

n main loads are:

Ø conditioning of ventilation air (supplyof fresh air)

Ø sensible internal loads: persons,equipment, artificial lighting

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

Ø solar loads (windows, glazings)

Ø conduction loads (walls, windows)

conditioning of ventilation air

solar loads

internal loads

supply air

return air



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

supply air temperature:18°C

supply air humidity:8 g/kg

requirements forconditioning of ventilationair at different sites

Fundamentals

Copenhagen Freiburg Trapani Bangkok0

102030405060708090

100cooling load of ventilation air

sensiblelatenttotal

sensible 0,57 1,95 5,93 28,48latent 1,43 2,88 17,59 69,33

total 2 4,84 23,52 97,81




Contents

F



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

atmosphereprinciple chilled water dehumidification of air and evaporative

coolingphase of sorbent solid liquid solid liquid 1)

typical materialpairs

water - silica gel,ammonia - salt 1)

water - water/lithiumbromide,ammonia/water

water - silica gel,water -lithiumchloride

water - calciumchloride, water -lithium chloride

market 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 60-90°C 80-110°C 45-95°C 45-70°Csolar 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




systemoverview

backupheater

chiller

heat supply system chilled water

conditioned airbuilding/roomreturnair

supplyair

ambientair

exhaustair

bufferstorage

des

icca

nt

wh

ee

l

hea

t re

cove

ry

wh

ee

l



liquid r

efrige

rant

low co

ncen

tration

high c

once

ntratio

n

.Q

C

.Q

G

.Q

A

.Q

Ev

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




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

n 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 smallcapacities

n driving temperature of single effect machines at> 85°C with COP of 0.6-0.7

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

status of absorptionchillers




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



status of adsorptionchillers


n adsorption chillers are market available fromto Japanese companies

n chilled water can be used for conditioning ofair (dehumidification, temperature decrease)or for cold supply in the rooms (fan coils,chilled ceilings,...)

n cooling capacity range 70 kW - 400 kW

n driving temperature starting at 55°C

n COP at design conditions 0.65



principles of opencooling cycles (desiccantcooling cycles)


n open cooling cycles use the effect ofevaporative cooling

n production of conditioned air (no chilledwater)

n potential for application of evaporativecooling is increased by dehumidification offresh air

n thermal energy required for regeneration ofthe sorbent (desiccant)

n separation of cooling and conditioning ofventilation air



status of desiccantcooling systems


n system components and complete systemsmarket available and employed since manyyears

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

n driving temperatures for regeneration usabledown to about 45°C

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

n adiabatic dehumidificationprocess



bypass

humidifiers

supplyair

returnair

dehumidifier heat recovery1 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 %



5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35

humidity ratio [g/kg]

05

1015202530354045505560657075

temperature [°C]

1

2

3

56

7

8

9

10

11

10 %

20 %

30 %

40 %50 %

70 %

100 %

4

bypass

humidifier

supplyair

returnair

dehumidifier heat recovery

heat

freshair

exhaustair

chilledwater

chilledwater

1 2 3 4 5 6

7811 910

desiccant coolingcycle for humidclimates




WINDOWS design tool




Teststand für Solare Sorptionsgestützte Klimatisierung (SSGK)

• 20 m2 Flachkollektoren (GreenOneTec/Sonnenkraft)

• 20 m2 Solarluftkollektoren (Grammer)

• 2,0 m3 Pufferspeicher (Solvis)

• Vermessung von Sorptionsrädern

• vielfältige Verschaltungsvarianten

• Entwicklung & Optimierung von Regelungsstrategien

•begleitende Systemsimulationen



modelling of sorptiondehumidifier


0 1 2 3 4 5 6 7 8 9 10

calculated dehumidification [g/kg]

0123456789

10measured dehumidification [g/kg]

1980 m3/h2790 m3/h3670 m3/hmanufacturer



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 collectorevacuated tube collectorsolar air collector

desiccantcooling

adsorption

single effect absorption

double effect absorption

ambient temperature25°C

collector radiation800 W/m2




Contents

F



solar assistedsystems

n solar collector system covers acertain fraction of regenerationheat

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

Solar air conditioning systems



Building Simulation(TRNSYS)

buildingdata

meteorological data

simulation of AC system

(CONVCOOL,SGKCOOL)

simulation of solar system(SOLCOOL)

cooling / heating load time series

driving energy time series

economic analysis(EXCEL)

solar fraction for cooling/

heating

energy balance,

costs


study on solar assisted airconditioning




climatic and load dataparameter Copenhagen Freiburg Trapanilatitude [° north] 55.8 48.0 37.9annual 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 Dec0

3

6

9

12

15

18cooling load [kWh/m^2]

CopenhagenFreiburgTrapani



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




heat recoveryCCh = compression chillerHT = heater (gas burner)

coolingloads

cold, dry

warm, humid

CCh HT

reference system with adiabatic cooling in return air



CT

heat recovery

CT = cooling towerAbCh = abs. chillerAdCh = ads. chillerHF = humidifier

coolingloads

cold, dry

warm, humid

AbChAdCh

aux.heater

HF

system with thermal driven chillers



humidifiers coolingloads

cool,dry

auxiliaryheater

warm,humid

dehumidifier heat recovery1 2 3 4 5 6

7891011

solar assisted desiccant cooling system (Copenhagen, Freiburg)




humidifiers

desiccant wheel

heat recovery

cooling loads

cold,dry

warm, humid

auxiliary heat

VPCCT VPC = vapour compr. chillerCT = cooling tower

solar assisteddesiccant coolingsystem (Trapani)





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




compared systems

ABV

ADV

ADF

DCF

DCSA

absorption chiller system with evacuated tubecollector

adsorption chiller system with evacuated tubecollector

adsorption chiller system with selective flat platecollector

desiccant cooling system with selective flat platecollector

desiccant cooling system with solar air collector



required collector area

specific collector area=collector area per floor area ofconditioned space


ABV ADV ADF DCF DCSA0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5specific required collector area

solar fraction cooling0,3 0,5 0,7 0,85

COPENHAGENABV ADV ADF DCF DCSA

0

0,1

0,2

0,3

0,4

0,5


solar fraction cooling0,3 0,5 0,7 0,85

FREIBURG


0,1

0,2

0,3

0,4

0,5


SFC0,30,50,70,85

TRAPANI



primary energy balance



25

50

75

100

125

150

175

200normalized primary energy demand [%]

solar fraction cooling0 0,3 0,5 0,7 0,85

COPENHAGEN

reference


25

50

75

100

125

150

175



FREIBURG

reference


25

50

75

100

125

150

175



TRAPANI

reference



electric peak load due toair conditioning


absorption/adsorption desiccant cooling0

25

50

75

100normalized maximum electric power [%]

Copenhagen Freiburg Trapani

100 % = reference system



simple pay back time



10

20

30

40

50

60

70

80simple payback time [a]


COPENHAGEN


10

20

30

40

50

60

70



FREIBURGABV ADV ADF DCF DCSA

0

10

20

30

40

50

60

70



TRAPANI



Solar autonomous desiccant cooling systems employing solar aircollectors

system integrated collector regeneration with ambient air


des i c cant w h e e l

h e a t r e c o v e r y w h e e l

cooling loads

cold, dry

warm,humid

humidif ierhumid i f i e r cool ing

loads

co ld , dry

warm, humid

des i c cant w h e e l

h e a t r e c o v e r y w h e e l



0

5

10

15

20

25

30

35

40

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

Feuchtegehalt X [ kg/kg ]

Tem

pera

tur

[ °C

]

T_operativ

T_luft

DIN 1946 T2

ϕ = 1,0

ϕ = 0,7

ϕ = 0,6ϕ = 0,5ϕ = 0,3 ϕ = 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 ]

Tem

pera

tur

[ °C

]

T_operativ

T_luft

DIN 1946 T2

ϕ = 1,0

ϕ = 0,7

ϕ = 0,6ϕ = 0,5ϕ = 0,3 ϕ = 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 temperaturen DIN 1946 part 2





Contents

F



built examples

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



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

built examples



technical data of the system in Sintra / Portugalbuilt examples

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 inFreiburg (university hospital) with adsorption cooling technology

built examples



schematic of thesystem in Freiburg

built examples




Contents

F



general results

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 airconditions (solar comfort improvement)

system design required which takes specific climaticconditions into consideration

summary & outlook

typcial value of requiredcollector area (office)

required solar fraction withsolar assisted systems

solar autonomous systems

system design



general results (continued)

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)

summary & outlook

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

n solar heat source is not constant (time dependanceof power and temperature)

n system control is more complex than for systemswith standard heating system (gas or oil burner)

n optimized control has a strong influence on systemperformance

summary & outlook

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 employ solar active equipment makes only sense ifpotentials of energy saving and reduction of coolingloads have been exploited

Buildingn reduction of internal loads (equipm., lighting)n advanced shading & daylighting conceptsn reduction of conduction loadsn reduction of leakages

A/C systemn separation of ventilation (handling of latent

loads) and cooling (handling of sensible loads)n employing heat (or enthalpy) recovery systemsn employing high efficiency chillers

needs for anintegrad approach

summary & outlook



outlooksummary & outlook

n solar thermal energy has a strong potential to beused for air conditioning in combination withcentralized A/C plants

n no technical solution for substitution of small splittype units available (if, then PV driven compression)

n research, development & demonstration required inorder to gain experience in design, control andoperation

n international collaborative work in the frameworkof the Solar Heating & Cooling Programme of theInternational Energy Agency (IEA): 11 countriesparticpate in Task 25 „Solar Assisted AirConditioning of Buildings“

air conditioning with solar energy - eduvinet · 1.3 definition of air conditioning 2 systems &...

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