Energy Performance and Optimisation
Tmopt program was used to couple the Tmsys simulations software with GenOpt, a generic optimisation program. Trnopt acts as an interface programme between the two software programs and streamlines the optimization process.
The optimisation process has as objective function the maximisation of the production of desalted water. The result is the optimal operating temperature of the fluid at the outlet of the solar field system coupled to the Rankine Cycle. This temperature has been optimised considering two different time periods: hourly or daily. The optimal daily and hourly temperature conditions are determined for both cycles considering two typical days corresponding to a typical situation in winter and in summer. The results for both cases are shown in Table 2 and Table 3.
As an example of the hourly results, Fig. 4 shows the results of the water system and working at a set point using the hourly and daily optimal temperatures in the selected summer day.
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Table 2. Performance of the system operating at the optimum daily temperature
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Table 3. Performance of the system operating at the optimum hourly temperature
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(b)
Fig. 4. Results for the optimal operating temperature of the fluid of the solar system. (a) daily (b)
hourly
A model for the optimal integration of Rankine cycles and solar thermal plants to drive Reverse Osmosis desalination plants has been presented. This model combines rigorous models for the simulation of the Rankine and solar field subsystems. The objective is to calculate the optimal operation temperature to produce the highest amount of desalted water. An example using trough solar collectors and water and pentane as working fluids was presented.
Using the trough solar collector and the two selected fluids the results in terms of energy efficiency and production of desalted water are very similar operating the system at an optimal hourly temperature at the collector’s outlet or at an optimal daily temperature. However, significant differences where found between the optimal temperatures in winter and summer days. So, this would mean that the set point for the solar field outlet temperature should be changed throughout the year to obtain the best global system performance but this change will have little effect throughout the same day. The performance using water is similar to that of n-pentane due to the high efficiency of the selected trough collector at high temperatures and the high solar radiation available in the selected geographical location. In the future the developed model will be extended to study also other types of solar collectors and working fluids.
This work is financially supported by the Ministerio de Educacion y Ciencia of Spain, OSMOSOL project, ref. ENE2005-08381-C03-03.
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