Sizing of solar cooling systems

funded by
Chapter C : Predesign – system sizing
Speaker: XXXX YYYYY
Training course on solar cooling
Chapter C : Predesign – system sizing 2
System sizing
Convection
Hygienic air
Internal load
Irradiance
Source : TECSOL
A) Building load characterisation needed

System sizing
Internal loads
System sizing

Solar collectors and thermally driven cooling
desiccant
adsorpti
on 1-effect
absorpti
on
2-effect
absorpti
on
SAC = solar air
coll.
CPC = stationary
CPC
FPC = selectively
coated flat plate
EHP = evacuated
heat-pipe
EDF = evacuated,
direct flow
SYC = stationary
concentrated,
Sydney-type
SAC = solar air
coll.
CPC = stationary
CPC
FPC = selectively
coated flat plate
EHP = evacuated
heat-pipe
EDF = evacuated,
direct flow
SYC = stationary
concentrated,
Sydney-type
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
∆T/G [Km
2
/W]
ηcoll
SYC
EDF
FPC
SAC
EHP
CPC
Source : Fraunhofer ISE
A) Choice of technologies
Solar production
0 25 50 75 100 125 150 175
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
flat-plate
evac. tube
evac. flat-plate
CPC-collector
parabolic trough
Irradiation:
800 W/m² direct normal
200 W/m² diffuse
efficiency
T - TAMB
[K] 60 80 100 120 140 160 180 200
0
100
200
300
400
500
600
700
800
900
1000
Barcelona
energyyield[kWh/m²]
temperature [°C]
FPC
EFPC
ETC
CPC
PTC
60 80 100 120 140 160 180 200
0
100
200
300
400
500
600
700
800
900
1000
Huelva
energyyield[kWh/m²]
temperature [°C]
FPC
EFPC
ETC
CPC
PTC
FPC: flate plate collector
EFPC: flate plate collector with concentrating parabolic compound (CPC)
ETC: vaccum tube collectors
CPC: vaccum tube collectors with concentrating parabolic compound (CPC)
PTC: parabolic trough collector
Source : Aiguasol

ProducedCold
rFactoConversion
ConsumedEnergyalConvencion
PEspec =
conveleccold
elec
eleccoldelec
elec
cold
elec
elec
conv,spec
COP
1
Q
Q1
Q
1Q
Q
Q
PE
εεε
ε
====
Specific Primary Energy (PE) (KWh PE/KWh cold):
Conversion factor: Electricity – 0.36; Fossil Fuel – 0.9
Conventional Compression Chiller:
Source : INETI
Primary energy analysis
Definitions
towercooling,spec
thermalfossil
sol
towercooling,spec
cold
heatdriving
fossil
sol
towercooling,spec
coldfossil
solheatdriving
towercooling,spec
coldfossil
backup
towercooling,spec
cold
fossil
backup
solar,spec
PE
COP.
)F-(1
PE
Q
Q)F-(1
PE
Q
1)F-(1Q
PE
Q
1Q
PE
Q
Q
PE
+=
+=
+=
+=
+=
ε
ε
ε
ε
ε
heatdriving
cold
thermal
Q
Q
COP =






+=
+
=
==
thermalelect
ercoolingtowspec,
cold
coldtdrivinghea
elect
ercoolingtowspec,
coldelect
edheatrejectercoolingtowspec,
cold
elect
ercoolingtow
ercoolingtow,spec
COP
1
1
E
Q
)QQ(E
Q
1QE
Q
E
PE
ε
ε
ε
ε
Solar Thermal Driven Chiller:
With:
Cooling tower:
Source : INETI
Definitions

0.0
0.5
1.0
1.5
2.0
2.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Solar Fraction for cooling
PEspec,sol,kWhPE/kWhcold
COP = 0.6
COP = 0.8
COP = 1.0
COP = 1.2
Conv 2
Conv, 1
COPconv =
2.5
COPconv =
4.5
heat source:
solar collector
+ fossil fueled
backup
primary
energy
conversion
factor for
electricity:
0.36
primary
energy
conversion
factor for
fossil fuels: 0.9
heat source:
solar collector
+ fossil fueled
backup
primary
energy
conversion
factor for
electricity:
0.36
primary
energy
conversion
factor for
fossil fuels: 0.9
Comparison between absortion and compression
Efficiency based on primary energy
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
solar fraction cooling
0
0.5
1
1.5
2
specific primary energy per unit of cold
conventional system
thermal system,
low COP
thermal system,
high COP
no primary
energy
saving
saves primary
energy
Source : Aiguasol

! High solar fraction for cooling necessary for solar thermally driven cooling
equipment with low COP which use a fossil fueled backup
! A lower solar fraction is acceptable if thermally driven cooling equipment with a
higher COP is employed
! An alternative is to use a conventional chiller as a backup (e.g. in case of a large
overall cooling power)
! Primary energy savings are always achieved using a solar thermally autonomous
systems but no guarantee for strictly keeping desired indoor comfort limits can
be given
! In any case the use of the solar collector should be maximised by supplying heat
also to other loads such as the heating system or hot water production
Consequences of primary energy performance
Design
Design with regard to solar-assisted air-conditioning mainly means
! Selection of the proper thermally driven cooling equipment for the
selected air-conditioning system
! Selection of the proper type of solar collectors for the selected air-
conditioning system and thermally driven cooling equipment
! Sizing of the solar collector field and other components of the solar
system with regard to energy and cost performance

Design approaches
‚Rules of thumb‘
Collector cost per heating
capacity
Cost of solar heat for
given climate
Load - gain - analysis for
given climate and load
Anual cost based on load-
gain-analysis
Computer design tool with
predefined systems
Open simulation platform
Accuracy,reliabilityofresults,detailsofdesigninformation
Requiredsysteminformation,effortforparametrization
Design point
design
design,cold
design,collcollcoll
COP
P
GA =η⋅⋅
==
>
designdesign,collcoll
spec
COPG
1
A
⋅η⋅
=
Example Gcoll = 800 W/m2
hcoll,design = 0.5
COPdesign = 0.7
==> Aspec = 3.57 m2
per kW cooling power

+ Method allows a very quick assessment (guess) about the
required collector area, if the efficiency of the collector and
the COP of the thermally driven cooling equipment is
known
– Method neglects completely the influence of the variation
of radiation on the collector during day and year
– Any information on the specific site and load is neglected
– Method neglects completely part load conditions of cooling
load in thermally driven cooling equipment
Advantages and disadvantages
Sizing
Source : EAW
Average values of the
specific collector area
" for Absorption- and
Adsorption chillers
3,0 to 3,5 m²/kW
chilling capacity
" for open technologies
(DEC, liquid DEC):
8 to 10 m² per 1.000 m³/h
rated air flowrate

Collector first cost
⊥⊥
−
⋅−
−
⋅−⋅Θ=η
G
)TT(
c
G
)TT(
cc)(k
2
ambav
2
ambav
10
⊥⊥
⊥
⋅η
=⇒
⋅η
=⇒⋅η⋅=
G
kW1
A
G
Q
AGAQ spec
use
use
&
&
specspecpower,heat CostACost ⋅=
incident
angle
modifier
optical
efficiency
linear
heat loss
coeff.
quadr.
heat loss
coeff.
average fluid
temperature
ambient air
temperature
radiation on
collector
specific
collector cost
average fluid temperature = operating hot temperature of cooling system
Collector cost versus specific required area
0
400
800
1200
1600
2000
1 2 3 4 5 6
required absorber area [m2
/kW]
collectorfirstcost[€/kW]
evacuated tube flat plate flat plate - integrated roof stationary CPC
Tav = 75°C
Gcoll = 800 W/m2

+ Method allows a rough comparison of different solar
collectors, if the collector parameters and the operation
temperature of the thermally driven cooling equipment are
known
– Method neglects completely the influence of the variation
of radiation on the collector during day and year
– Any information on the specific site and load is neglected
– Method neglects completely part load of cooling load and
thermally driven cooling equipment
Solar heat cost
annuityspecannual fCostCost ⋅=
gross
annual
heat
Q
Cost
Cost =
annual
collector cost
spedific
collector cost
(€/m2
)
annuity
factor
solar heat
cost (€/kWh
of heat)
collector gross
heat
production
.dataicallogmeteoroatingmindotheofvalueshourlygsinucalculatedTypically
.etemperaturoperationgivenaandsitegivenaatproductionheatcollectorannualQgross =

Solar heat cost
0
4
8
12
16
20
0 200 400 600 800 1000 1200 1400
annual gross heat production [kWh/m2
]
heatcost[€-cent/kWh]
etc fpc irc cpc Palermo, Tav = 75°C
Solar heat cost
0
4
8
12
16
20
0 200 400 600 800 1000 1200 1400
annual gross heat production [kWh/m2
]
heatcost[€-cent/kWh]
etc fpc irc cpc Palermo, Tav = 95°C

Simple software tool SHC (NEGST project)
Only needs monthly cooling (heating) load
Free download in:
http://www.swt-technologie.de/html/publicdeliverables3.html
Compares monthly loads
(heating and coling) with
monthly solar energy
gains.
It is based on
PHIBARFCHART Method
- The results are primary
energy savings for
colector area installed.
+ Method allows a good comparison of different solar
collectors using their parameters and the radiation data of
a specific site
+ The maximum possible heat production of a specific solar
collector for a given site (annual meteorological data file)
and a given constant operation temperature is determined
– Any information about the load profile is neglected
– Method neglects completely part load of cooling load and
thermally driven cooling equipment

meteo data
building
model
collector
model
solar fractions for
heating and cooling
COP, ε
heatload
solar gains
0
50
100
150
200
250
0 100 200 300 400 500 600 700 800
heating cooling 1 0.5 0.25 0.1
! For each hour of the year
the required heat for
cooling (heating) is
computed, e.g. using
building simulation
! Global efficiency factors for
transformation of heat in
cooling (heating) are used
to describe the technical
equipment
! Calculation of hourly
collector gains using
different operation
temperatures for cooling
and heating
Correlation of loads and gains
Software tools needed to determine hourly
cooling (heating) loads of a building
TRNSYS – Commercially available
(www.sel.me.wisc.edu/trnsys/)
Energy plus – Download free
(www.eere.energy.gov/buildings/energyplus/ )
ESP-r – Download free
(http://www.esru.strath.ac.uk/Programs/ESP-r.htm )
A list of other software tools can be found :
(http://www.eere.energy.gov/buildings/tools_directory/)

Simple software tools using hourly
cooling (heating) load
SACE Cooling evaluation light tool
– available in http://www.solair-project.eu/218.0.html
Results using this software tool while be shown latter
Simple software tools using hourly
cooling (heating) load
SolAC – available in:
http://www.iea-shc-task25.org/english/hps6/index.html
Four different units are considered in this software:
• Solar system
• Cooling device
• Air handling unit
• Cooling and heating components in the room
The input data for the
programme is:
• weather data including solar
radiation (hourly data)
• load files including heating
and cooling loads (hourly
data)

Dynamic simulation software tools using
hourly cooling (heating) load
- System orientated
TNSYS - www.sel.me.wisc.edu/trnsys/
ColSim - www.colsim.de
Insel - http://www.inseldi.com/index.php?id=21&L=1
- Building Orientated
Energy plus - www.eere.energy.gov/buildings/energyplus/
Software Solar
Components
AC
Components
New
Components
Free
downlaod
Open
source
code
TRNSYS Yes Yes Yes No Yes
ColSim Yes Yes, but no
clear list was
possible to
obtain.
Yes Not clear Yes
Energy
Plus
Yes Yes Yes Yes Not clear
INSEL Yes Yes Yes NO NO
Identification of HVAC components available which are most interesting for
CTSS
TRNSYS 16.
Type 107 – Absorption Chiller (hot water fired, single effect)
Type 51 – Cooling Towers.
TESS Libraries
Type 680 – Single-effect hot water-fired absorption chiller (Equivalent to type
107 of TRNSYS 16)
Type 679 – Single-effect steam-fired absorption chiller
Type 677 – Double-effect hot water-fired absorption chiller
Type 676 – Double-effect steam-fired absorption chiller
Type 683 – Rotary desiccant dehumidifier – models a rotary dessicant
dehumidifier containing nominal silica gel.

solar
gas
elect
caldera
bomba
calor
absorció
calefacció
refrigeració
solar
gas
elect
caldera
bomba
calor
absorció
calefacció
refrigeració
Source : Aiguasol
Calculation methods :
Estimated calculation with energy balances
Solar thermal energy availability
• Simulation tool for the solar systems
• “Infinite” consumption with high return temperature (chilled water)
• 100% use of produced solar energy
Energy load determination, per year and per month: cold, heat, and DHW
• Calculation tool for the building energy load
• DHW energy load determination
Use factor determination
• Depends on the relation availability / load
• Depends on the heat storage
Definition of energy flows between subsystems
• -> Definition of a control strategy
Chapter C : Predesign – system sizing 32Source : Fraunhofer ISE

Guidelines for design, control & operation
of solar assisted adsorption chillers
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
60 65 70 75 80 85 90 95
temperature, °C
COP,COPsol,etacoll
20
30
40
50
60
70
80
90
coolingpower,kW
etacoll COP
COPsol cooling power
COPsol =
COP * ηcoll
Radiation on
collector: 800 W/m
2
COPsol =
COP * ηcoll
Radiation on
collector: 800 W/m
2
COP-maximum
at about 70°C
Efficiency of solar thermal cooling systems
0.00
0.10
0.20
0.30
0.40
0.50
0.60
60 80 100 120 140 160 180 200
Working temperature [°C]
COPsolar
500
600
700
800
900
1000
Irradiation W/m2
==> optimal
working
temperature
depends on the
irradiation level

Evaluation parameter: Costs of saved
primary energy
! Combined Energy-costs-Performance
! enables comparison of different system designs
Costs of primary
energy saved
=
∆ Total annual costs
∆ Primary energy
∆primary energy = annual primary energy saving of
the solar driven system compared to a
conventional reference system
∆primary energy = annual primary energy saving of
the solar driven system compared to a
∆total annual costs = annual supplementary costs of the solar
driven system compared to a
∆total annual costs = annual supplementary costs of the solar
driven system compared to a
10%
20%
30%
40%
50%
60%
55 65 75 85 95 105 115 125 135
Storage volume, l/m
2
Primaryenergysaved
160 180 200 220 240 260 280
! Madrid
! Office
buildings
! Flat plate
collector
! Backup:
Gas boiler
! Absorption
chiller
Collector surface,
m2
Example: primary energy savings
(in%ofthereferencesystem)
Growing collector
surface

140%
145%
150%
155%
160%
165%
170%
175%
180%
55 65 75 85 95 105 115 125 135
Speichervolumen, l/m2
Jahreskosten,%Referenz
160 180 200 220 240 260 280
Kollektorfläche,
m2
ansteigende
Kollektorfläche
Example: annual costs
! Madrid
! Bürogebäude
! Flachkollektor
! Backup:
Gaskessel
! Absorptions-
kältemaschine
! Madrid
! Office
buildings
! Flat plate
collector
! Backup:
Gas boiler
! Absorption
chiller
Growing collector
surface
Collector surface,
m2
Storage volume l/m2
Annualcosts,%reference
0.12
0.14
0.16
0.18
0.2
0.22
0.24
0.26
0.28
55 65 75 85 95 105 115 125 135
Speichervolumen, l/m2
KosteneingespartePE,€/kWh
160 180 200 220 240 260 280
Kollektorfläche,
m2
Minimu
m
Example: Costs of primary energy savings
! Madrid
! Bürogebäude
! Flachkollektor
! Backup:
Gaskessel
! Absorptions-
kältemaschine
! Madrid
! Office
buildings
! Flat plate
collector
! Backup:
Gas boiler
! Absorption
chiller
Storage volume l/m2
Collector surface,
m2
Costsofprimaryenergysaved,€/kWh

Dynamic modelling with TRNSYS… necessary
System sizing
Transient simulation – TRNSYS
TRNSYS features
– Numerical calculation methods
– Continuous yearly simulation of the thermal behaviour of the
installation, analysing the transitory phenomenon of the heat
flows
– Variability of climatology (temperature, irradiation) is taken into
account
– Enables analysis of the different factors which determine the
energetic behaviour of the system # parametric study#
optimisation

TRNSYS Workspace
Results obtained with TRNSYS

Analysis of the results
0
5
10
15
20
25
30
35
1 14 27 40 53 66 79 92 105 118 131 144 157
Tamb
Tair
0
1000
2000
3000
4000
5000
6000
7000
Gener Febrer Març Abril Maig Juny Juliol Agost Setembre Octubre NovembreDesembre
kWh
Monthly heating demand in kWh
Total demand in kWh
Solar contribution in kWh
Calculation options with dynamic simulation tools
Separated calculation of building and cooling system
– Step 1: Simulation of the building demand (heating, cooling)
– Cooling system model= ideal system with infinite power.
– Intermediate result: hourly data of heating and cooling demand.
– Step 2: Simulation of the cooling system
– Result: energy contribution of the real cooling system
Coupled calculation of the building and the cooling system
– Simulation of the building (demand) and of the cooling system in the
same software
– Cooling system model = real system
– Results:
• Energy contribution of the real cooling system
• Degree of fulfilment of the comfort criteria

Which questions have to be answered?
1. Which is the basic sizing of the main equipments?
• Collector field : type and size in m2
• Absorption machine: kWf
2. What is the solar contribution to the cooling, heating and global demand?
3. Which is the basic sizing of the back-up system?
• type (boiler, heat pump, air conditioner...);
• size kW
4. Which are the energy savings?
5. What are the additional costs compared to a conventional installation?
6. What is the pay-back time?

Sizing of the absorption machine
f
f
solar
gensolar
gen
f
kW
m
m
kW
kW
kW
m
kW
kW
kW 2
22
332.015.065.0 ==××
Demand peak < maximal total power (absorption + auxiliaries) + cold
storage
Operating with solar energy: minimal power required to absorb the
solar heat produced and convert it into cold. # 3 m2/kWf
– Criteria 1: the absorption machine is able to use the maximal
solar production. Solar peak production approx. 0.5 kW/m2
(1000 W/m² x 50 % efficiency)
– Criteria 2: the solar energy produced during the day of maximal
irradiation can be totally used by the absorption machine,
assuming that the required heat storage is available
– Maximal power to guarantee a minimal solar contribution
(typically > 60...70 %) and/or an reasonable number of operating
hours (> 1000 h/year).
Rules of Thumb – pre-design rules of
solar cooling systems
Sizing of the heat/cold storage
Cold storage
– Cover demand peaks (smaller machines, larger number of
operating hours)
– Avoid part-load or intermittent operation
Heat storage
– Gap between cooling demand and solar heat availability
– Guarantee continuous operation of the machine during days of
intermittent irradiation
– Typical size: 25 .. 50 litres / m2 of collector

Control strategy
Starting priority (cold production) according to the energy efficiency
– Cold production with heat-pump in case of simultaneous heat
demand. Solar contribution for space heating.
– Cold production with absorption through solar heat
– Cold production with heat-pump (without heat recovery)
– Cold production with absorption through gas boiler
System sizing
75 – 95°C
75 – 95°C
25 - 35°C
7 – 12 °C
700W/m² 85 kW
77 kW
50
kWf
127 kW
200 m²
Source : TECSOL

System sizing
! 1 Cooling load : 50 kWc
! 2 Inlet generator : 50 / 0.65 = 77 kW
! 3 Cooling tower : 77 + 50 = 127 kW
! 4 Primary loop efficiency : 0.9
! 5 Heat load on collector side : 85 kW
! 6 Average irradiance : 700 W/m²
! 7 Collector efficiency : 0.6
! 8 Collector area : 85/0.7/0.6 = 200 m²
! 9 Optimal tilt : 30° (France South)
! 10 Groung space necessary > 300 m²
Check list concept : example
233
Possible undersizement of solar system thanks to
back up
333Passives actions decrease potential
223Yearly heating and DHW needs
223Yearly adequation production <-> load
133Daily adequation production <-> load
Load
TECHNICAL
FEASIBILITY
333Adapted existing material (or planned) for back up
233Adapted distribution network
123Space for technical premices
223Important area for solar collection
333Climate
Building
HotelPublic buildingIndustry
Source : TECSOL

455558
TOTAL SCORE
(on 63) :
232Presence of a long term financed monitoringMonitoring
223Regulat operation action possibilitiesFEASIBILITY
223Skilled internal technical staff
O&M
ORGANISAT.
133Financial stability of building owner
231National & international supports eligibility
333Environmental action politics
323Importance in term of marketing impactFEASIBILITY
333Building owner motivationECONOMICAL
133High investment capacity
Building owner
223Low water cost
331High cost of saved energy
Cost of energy
HotelPublic buildingIndustry
Check list concept : example
Source : TECSOL
Disclaimer
This training has been developed in the context of SOLAIR. SOLAIR is a European co-
operation project for increasing the market implementation of solar-air-conditioning
systems for small and medium applications in residential and commercial buildings. For
further information on the project or on products of the project see: www.solair-
project.eu
The project SOLAIR is supported by the Intelligent Energy – Europe (IEE) programme of
the European Union promoting energy efficiency and renewables. More details on the
IEE programme can be found on: http://ec.europa.eu/energy/intelligent/index_en.html
The sole responsibility for the content of this training lies with the authors. It does not
represent the opinion of the European Communities. The European Commission is not
responsible for any use that may be made of the information contained therein.

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