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.

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.

Why Solar Cooling for Agro-Food Industry (AFI)?  Why it is interesting for Agro-food Industry?  Why it is interesting for Solar Cooling?

Why it is interesting for Agro-food Industry? TUNISIAMOROCCOEGYPT AFI’s structure companies with over 10 employees - 60,000 employees - 2,016 companies (24% of industrial companies), - 95% of them are SME - 110,000 employees companies, including 178 public ones - 440,000 employees AFI’s market - 2 nd 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) AFI’s energy situation - Primary Energy Consumption: TOE (2 036 GWh) - Primary sources: electricity (52%) and oil (33%) - Primary Energy for Electricity production : TOE (348 GWh ) - Primary energy consumption: TOE, including GWh (450,000 TOE) of electricity - Primary consumption should increase by 15% to 20% over next decade  The AFI is a major industrial sector in all three EMT countries, accounting for between 12% and 15% of the gross domestic product (GDP).  Cold chain should be granted to ensure product quality for exporting purpose.  The AFI sector requires high energy supply, specially for cooling processes.  Energy demand of the AFI is expected to increase steadily during the next two decades.  Solar cooling have a great energy saving potential.

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). source: EECCAC Split >12 kW 7% RAC <12 kW 36% VRF 2% Roof tops 5% packages 5% Chiller 45%

How did we start?  Load Profile (SF)  Integratrion with existing systems Agro-Food Sector characterisation  Location Suitability Land Solar radiation  Level of interest  Dairy  Fruits & Vegetables  Fish & Meat  Oil  Bevarage Plant Selection Process Selection  Refrigeration load at 0°C Distributed along the year, Peaking during summer.  Replication Potential. End User Requirement Agro-Food Sector characterisation

How to design a solar cooling system Rules of thumb cannot be applied For solar cooling design D 5.2 Medisco Design Guidelines D 3.4 Medisco Simulation tool

Solar Cooling: General Scheme Thermal Driven process Heat Cold Water Air-conditioning Heat storage? Heat rejection? Cold Storage? Load? Source: ISE Fraunhofer

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)

 1. Cooling Load Temperature. (-10°C – 5°C)  2. Good performance at different ambient tempeartures.  3. Dry cooling for heat rejection (water scarcity) The Absorption Chiller DRY COOLER  ROBUR absorption chiller,  Air cooled, Single stage  Ammonia-water 13,3kW,  (T EXT 30°C)  Min. Operating temp =-10°C Source: Robur

 Starting from the working temperature range of the generator of the chiller, that is 150 °C-180°C, a pre-selection of typologies of collectors has been done. Three kinds of solar collectors have been investigated:  Parabolic trough collectors  Fresnel-type collectors  Evacuated tube collectors with compound parabolic concentrator How to select the solar collector? I Collector efficiency for the respective application should amount to at least 50%. collector technology efficiency curve When deciding which collector technology is best suited for a particular cooling technology, efficiency curve play and important role for the various collectors. Consider the direct solar radiation in the specific geographical location

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.

Which thermal fluid? WaterOil Fluid cost to 10 €/L Specific heat kJ/kg.K viscosity+++- Pressure---++

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. 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). Capsule Charging Ice-encapsulated storage 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.

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.

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Kindergarten in Milan - Italy driving heat high temperature, T H useful cooling low temperature, T C heat rejection intermediate temperature, T M

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?

Absorption cooling analysis Thermodynamic analysis reveals the need for medium temperature and single stage absorption chiller Evacuated tubes Flat Plate Medium T.

Source: Pridasawas, KTH, 2006 How to select the chiller?