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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 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 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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Systems & Components
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)
Systems & Components
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
Systems&Components
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adsorption chiller cycle
Systems & Components
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
Systems & Components
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)
Systems & Components
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
Systems & Components
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
Systems & Components
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
dehumidifier heat recovery
heat
freshair
exhaustair
chilled
water
chilled
water
1 2 3 4 5 6
7811 910
desiccant coolingcycle for humidclimates
Systems & Components
Systems & Components
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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
Systems & Components
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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
Systems & Components
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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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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 cooling
2.3 Solar collectors
3 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 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
Solar air conditioning system
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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
Solar air conditioning system
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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
Solar air conditioning system
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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
Solar air conditioning system
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humidifierscoolingloads
cool,dry
auxiliaryheater
warm,humid
dehumidifier heat recovery
1 2 3 4 5 6
7891011
solar assisted desiccant cooling system (Copenhagen, Freiburg)
l i d
Solar air conditioning system
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humidifiers
desiccantwheel
heat recovery
cooling
loadscold,dry
warm,humid
auxiliaryheat
VPCCTVPC = vapour compr. chillerCT = cooling tower
solar assisteddesiccant coolingsystem (Trapani)
Solar air conditioning system
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
Solar air conditioning system
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
Solar air conditioning system
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
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
FREIBURG
reference
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
TRAPANI
reference
electricpeakloaddueto
Solar air conditioning system
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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
Solar air conditioning system
80simple payback time [a] TRAPANI
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simple pay back time
ABV ADV ADF DCF DCSA0
10
20
30
40
50
60
70
80simple payback time [a]
solar fraction cooling
0 0,3 0,5 0,7 0,85
COPENHAGEN
ABV ADV ADF DCF DCSA0
10
20
30
40
50
60
70
80simple payback time [a]
solar fraction cooling
0 0,3 0,5 0,7 0,85
FREIBURG
ABV ADV ADF DCF DCSA0
10
20
30
40
50
60
70
80solar fraction cooling
0 0,3 0,5 0,7 0,85
Solarautonomousdesiccantcoolingsystemsemployingsolarair
Solar air conditioning system
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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
Solar air conditioning system
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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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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 cooling
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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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 cooling
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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