Solar cooling for Mediterranean Countries Integration of solar concentrating systems and absorption cycle technology

1. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Solar cooling for Mediterranean CountriesIntegration of solar concentrating systems and absorption cycle technology

2. What’s Solar Cooling? The core idea is to use the solar energy directly to produce chilled water. The high temperature required by absorption chillers is provided by solar troughs. The system doesn’t require “strategic” materials (like in PV systems) and has peak production in the moment of peak demand. Chilled water Heat Transfer Fluid

3. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Main Components Absorption Chiller (AC) An absorption chiller is a device that uses a heat source to separate a volatile substance from the liquid substance in which is dissolved. The vapor is condensed outside and then the liquid evaporates in an exchanger where the water to be chilled flows. The vapor is then dissolved again in the main liquid substance. The chiller output is a cooled liquid at a temperature of -5°.The use of a pump to increase the moisture pressure leads to low electricity consumption. In solar cooling the heat for the separation is provided by a Heat Transfer Fluid (HTF), for example in this simulation it has been assumed diathermic oil.

4. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Absorption Chillers Cooling Power The cooling power of Water-Ammonia Absorption Chiller is influenced by the mass flow and the temperature of the oil and by the external temperature that affects the cooling of the machine Data from Robur SPA

5. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Main Components Parabolic Linear Collectors (PLC) A parabolic mirror concentrates the sun on a dark painted pipe placed in the focus of the parabola. The insulation may provided by a front glass that protects the reflecting surface and by a circular tube around the pipe, that allows vacuum insulation between them. The temperature upper limit is imposed by piping materials.

6. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Parabolic Linear Collectors Power delivered (1 array-4 rows-8 PLCs- 54m2) The power outpiut of the PLC is mainly influenced by the heat losses, so a higher difference between HTF temperature and external temperature increases the heat losses and affects the efficiency. Data from SHAP srl

7. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Parabolic Linear Collectors

8. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Other Components Oil Tank – it works as expansion vessel and it is possible to use it for heat storage. In this case the dimensions of the tank and the quantity of HTF are critical. Other systems, using phase-changing mixtures, are under study. Burner – it can provide the heat when the request is higher than the power provided by the sun. It allows: a fast startup at sunrise, working of ACs during sunset hours or even night hours, fast activation to maintain the power feeding in case of clouds’ shading. Pumps – variable flow pumps for hot HTF (upper limit 350°C). With an inverter it allows constant head with variable flow and so a fine reglation of the circuit without energy waste.

9. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Configuration of the collectors array For the solar collector array, two orientations are possible: -Axis on N-S direction and “daily” tracking -Axis on E-W direction and “seasonal” tracking The choice is driven by two considerations: -The different energetic behaviour -The availability of free room for installation

10. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Configuration of the collectors array N-S axis configuration has a higher yield but the winter season yield is lower and it emphatizes the energy peaks in summertime E-W axis configuration has a smoother behaviour during the year

11. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili The control strategy The major issue of this kind of plant is the control. In fact the driving parameters (user request, solar power and external temperature) are uncontrollable and not completely predictable. Beside this, each component has different reaction to input parameter changes (HTF temperature, mass flow, external temperature) and so a working point that optimizes the plant reacting to the oscillations in driving parameters is hard to maintain! A program to optimize the plant layout and the control strategy is needed. A precise simulation of the plant and a model for simulating the driving parameters has been developed.

12. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili The Model setup The model for each component will be implemented in Simulink® according to the data available from the manufacturers. Rough models are already available for most of them. Once the blocks are ready, they can be assembled in various configurations of plant in order to simulate the production and the behavior of the plant. The simulation step is one hour, the simulation period is one year. Lower steps are available in order to investigate the transient behavior of the plant components. A Meteorogical block provides radiation and external air temperature. The results with different regulation strategy can be compared.

13. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili The Meteorologicaldata NASA- SSE The Meteorological data comes from NASA-SSE (Surface meteorology and Solar Energy) data set. They are monthly averaged data on a ten years period on a 1° x 1° grid. The data are assumed constant in the cell of 1°x 1° (111 km x 111 km), this means that they have to be integrated using ground measured data,where they are available. Available data of temperature, total and diffuse radiation have been used, wind speed at 10m on flat terrain will be used in future for structural calculations and heat exchange with external air.

14. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili The Meteorologicalmodel Meterological Input Data Meterological Output Data H _Daily horizontal global radiation H _ Daily horizontal diffuse radiation d Geometrical location data Temperature information

15. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili The model for the plant simulation Model description -Steady state simulation on time step -Possibility to change time step size form 1 hour to few minutes -Possibility to run model to simulate year or daily behavior Input: -Devices parameters -Weather parameters Output: -Temperature history in critical points -Energy yield

16. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Layouts for the plant simulation A plant has been dimensioned on a real site, Hyrghada (Egypt) (27°14’N;33°49’E) • Two layouts have been investigated: • Single collector array and single absorption chiller unit • Multiple collector array and several absorption chiller units with possibility to switch on only some according to the available solar power or user request.

17. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Single PLCs array results In summer days peak hours the power provided to the plant by PLCs may exceed the power consumption of ACs. This may lead to overheating. In order to avoid overheating, the protection system is based on defocusing of some rows of collector field or using a second load to absorb the PLC power output peaks. The secondary load can be an additional power to hot water production, that is already feasible as cogeneration production from the standard plant.

18. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Multiple PLCs arrays results: Yearly Performance 6 PLCs and 8 ACs The cycle is activated as the solar radiation exceed the defined thresholds. The CO2 saved has been obtained considering that the electric power is obtained on the site by diesel engines (assumed efficiency 0.3) and comparing it with the option of the compression chillers with COP=3

19. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Multiple PLCs arrays The optimization of this plant on an energetic, environmental and economic point of view has led to a solution with 6 PLC array (6x54m2) and 8 AC (8x17kW); 2-4-6 or 8 ACs are turned on according to the availability of energy. Power demand and plant output along a typical day (result obtained using NASA-SSE data set, d=185 and load peak fit to chiller output peak) Pload=1014 [kWh] Pout, plan=702 [kWh] Solar Fraction=69 %

20. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Daily Performance – 19th July Blue:External Temperature Green: Power collected by PLCs Red: Power exploited by ACs Cyan: Cooling Power Number of ACs active

21. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Daily Performance - 1st November Blue: External Temperature Green: Power collected by PLCs Red: Power exploited by ACs Cyan: Cooling Power Number of ACs active

22. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Conclusions -Solar Cooling main components have different optimisation point for HTF temperature and mass flow rate. A control strategy to keep the plant at optimisation point despite of oscillation in driving parameters is needed. -For sites with peak irradiation around 1000 kW/m2 a good matching can be obtained with a little water-ammonia absorption chiller and a 54 m2 PLC array. -The best matching can be obtained with some PLC arrays and a number of ACs slightly higher but above all having the possibility to switch on only some ACs, as few ACs at full load have a higher yield than more ACs at partial load.

23. C.R.E.A.R. Centro interdipartimentale di Ricerca per le Energie Alternative e Rinnovabili Acknowledgments -Italian Ministero dell’Ambiente for supporting and financing the project -Shap srl for the data about solar collectors -Robur spa for the data from the experimental measurements they did after our request -NASA for the availability of meteo data for academic institutions -You all for the attention!