Peculiarities of solar cooling systems:
MEDISCO DESIGN GUIDELINES
Osama Ayadi
Dipartimento di Energia, Politecnico di Milano
CONTENTS
 Introduction
 Why Solar Cooling for Agro-food Sector?









How to design a solar cooling system?
Solar cooling General Scheme
Medisco Concept
Medisco Subsystems
Absorption Chiller
Solar Collector Selection
Cold Storage
Integration with the existing system.
Conclusion
.
osama.ayadi@polimi.it
Introduction
 During the project, two experimental sets up, with novel high
performing solar driven cooling and refrigeration concepts, have been
constructed and installed allowing on site monitoring activities of the
system performance.
 The experiences gained through the design and the experimental
activities have been used to create these design guidelines in order to
disseminate the best practice applications for next solar-cooling
installations in this area.
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Why Solar Cooling for Agro-Food Industry (AFI)?
Why it is interesting for Agro-food Industry?
Why it is interesting for Solar Cooling?
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Why it is interesting for Agro-food Industry?
AFI’s
structure
AFI’s market
AFI’s energy
situation
TUNISIA
MOROCCO
EGYPT
- 945 companies with
over 10 employees
- 60,000 employees
- 2,016 companies (24% of
industrial companies),
- 95% of them are SME
- 110,000 employees
- 920 companies,
including 178 public
ones
- 440,000 employees
- 2nd industrial sector,
with strong exports
- investment in the AFI is
increasing
- one of the main sectors
of the country’s economy,
but exports only 17% of
production (quality and
health issues)
- milk and dairy
products represent main
AFI production AFI
(7,954,000 t/y)
- Primary Energy for
Electricity production : 29
827 TOE (348 GWh )
- Primary energy
consumption: 2 440 000
TOE, including 5 250
GWh (450,000 TOE) of
electricity
- Primary consumption
should increase by 15%
to 20% over next
decade
- Primary Energy
Consumption: 174 574
TOE (2 036 GWh)
- Primary sources:
electricity (52%) and oil
(33%)
The AFI sector
requires
high energy
specially
for cooling processes.
is a major
industrial
sector insupply,
all three
EMT countries,
accounting
for between
12%is and
15% of
grosssteadily
domestic
product
Energy
demand
of the AFI
expected
to the
increase
during
the (GDP)
next .
two
Colddecades.
chain should be granted to ensure product quality for exporting purpose.
Solar cooling have a great energy saving potential.
osama.ayadi@polimi.it
Why it is interesting for Solar Cooling?
Several solar cooling technologies can cover the cooling
demand at the high temperature range.
There is a high potential and advantages for cooling at low
temperatures due to a significant economy of scale (i.e.,
refrigeration technologies represent a large share of the
investment and operation costs).
Split >12 kW 7%
RAC <12 kW 36%
Chiller 45%
VRF 2%
Roof tops 5%
packages 5%
source: EECCAC
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How did we start?
 Location Suitability
Land
Solar radiation
Level of interest
Agro-Food Sector
characterisation
Plant
Selection
Dairy
Fruits & Vegetables
Fish & Meat
Oil
Bevarage
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Process
Selection
Load Profile (SF)
Integratrion with
existing systems
End User
Requirement
Refrigeration load at 0°C
Distributed along the year,
Peaking during summer.
Replication Potential.
How to design a solar cooling system
Rules of thumb
cannot be applied
For solar cooling D 5.2 Medisco
design
Design Guidelines
D 3.4 Medisco
Simulation tool
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Solar Cooling: General Scheme
Air-conditioning
Heat
Thermal
Driven
process
Cold Water
Heat
storage?
Heat
Cold
rejection? Storage?
Load?
Source: ISE Fraunhofer
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MEDISCO Concept Scheme
Requirements
High driving temperatures =>
Concentrating Solar Collectors, for high direct radiation sites
Advantages
Heat rejection by dry air (no water needs, low maintenance effort)
Ice storage (high storage capacity; high mismatch between
cooling loads and solar gains is allowed)
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The Absorption Chiller
 1. Cooling Load Temperature. (-10°C – 5°C)
 2. Good performance at different ambient tempeartures.
DRY COOLER
 3. Dry cooling for heat rejection (water scarcity)





Source: Robur
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ROBUR absorption chiller,
Air cooled, Single stage
Ammonia-water 13,3kW,
COP=0,65 @ (TEXT30°C)
Min. Operating temp =-10°C
How to select the solar collector? I
 Starting
from
the working
temperature
range is
of the generator of the chiller,
When
deciding
which
collector
technology
is 150
a pre-selection
of typologies of collectors has been
best that
suited
for °C-180°C,
a particular
cooling technology,
Consider the direct
done.
Three
kinds
of
solar
collectors
have
been
investigated:
efficiency curve play and important role for the
solar radiation in the

Parabolic
trough
collectors
various collectors.
specific geographical
 Fresnel-type collectors
location

Evacuated tube collectors with compound parabolic concentrator
Collector Efficiency Curve
PTC I
PTC II
LFR
CPC I
CPC II
CPC III
FPC I
FPC II
Efficiency
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
50
100
150
200
250
dT [Tavg. fluid - Tamb.] °C
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300
Collector efficiency
for the respective
application should
amount to at least
50%.
How to select the solar collector? II

Selection is based both technical and economic aspects.
Important parameters include :
 Thermal performance
 Availability
 Cost and delivery time.
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Which thermal fluid?
Water
Oil
Fluid cost
+++
Specific heat
kJ/kg.K
+++
--4 to 10 €/L
--
viscosity
+++
-
Pressure
---
++
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How to select the cold storage?
 Ability to store cold at the chiller operating
temperature.
 Storage capacity
 Shortage of solar radiation.
 Mismatch between solar gain and load.
 Available space.
 Cost.
Capsule Charging
The low operating temperatures of the Medisco solar cooling
system(-10°C) allows storing the cold energy in Ice storage.
The advantage of this ice storage is the use of the latent heat
of fusion of water (-335 kJ/kg), and thus its size is compact
(10 to 20% of a comparable chilled water tank).
Ice-encapsulated storage
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Capsule Discharging
Chilled Water Storage
Chilled water storage systems use the sensible heat capacity of water
store to store cooling energy.
The most economical for systems greater than 7000kWh in capacity.
The storage energy density of a chilled water storage unit is given by
the heat capacity of water.
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Conclusion
MEDISCO concept is air-cooled 
no water consumption nor complex
regulatory requirements
MEDISCO concept require hot temperatures 
Concentrating solar collectors work
perfectly in required area.
The potential to work at low temperatures satisfy the
requirement of most of the AFI processes.
As well as allow to store cold energy in ice storage,
which can cope with high mismatch between cooling
production and consumption.
osama.ayadi@polimi.it
‫شكراً لكم‬
Thank You
osama.ayadi@polimi.it
Kindergarten in Milan - Italy
driving heat
high
temperature,
TH
heat rejection
intermediate
temperature,
TM
useful cooling
low
temperature,
TC
osama.ayadi@polimi.it
Low and High temperature lift
Q. Is it possible to provide low temperature solar refrigeration to the industrial
processes?
Q. Which solar and refrigeration technologies can be used for industrial applications?
osama.ayadi@polimi.it
Absorption cooling analysis
Thermodynamic analysis reveals the need for medium temperature and
single stage absorption chiller
400
COP /
350
0.7 / 0.3
300
0.7 / 0.4
1.1 / 0.3
250
Thigh, °C
η Carnot
1.1 / 0.4
Medium T.
200
150
High temperature lift
systems, e.g. ice storage
in hot climate
Evacuated tubes
100
Flat Plate
50
0
10
15
20
25
30
35
40
45
50
55
Δ = Tm edium - Tlow , °C
COPideal
Tlow Thigh  Tmedium 

Thigh Tmedium  Tlow 
 carnot 
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COP
COPideal
How to select the chiller?
Dessicant cycle
Ejector cycle
20°C
300°C
Concentrating
heat
Solar Thermal
Collectors
-Flat Plate
-Evacuated Tube
-Concentrating
Rankine cycle
Air-conditioning
15°C
150°C
ETC
Adsorption
100°C
Flat Plate
70°C
8°C
Absorption
Chemical reaction
Food,
Vaccine Storage
0°C
Thermo-electric cycle
Photovoltaics
Freezing
electricity
Vapour compression
Stirling cycle
Source: Pridasawas, KTH, 2006
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