Description of the program

From the data recorded on the computer, it has been developed a program that let us manage, visualize and interpret all the collected information. La principal screen, consist of a date selector on the left part, where the day and the time range (starting and ending hours and minutes) we want to be analyzed is introduced. In view of eventual looses of data the interpolation period can be fixed, which has been stabilised in 10 minutes by default, as a sufficient margin so as to represent the behaviour of the installation without substantial modifications.

On the upper part can be seen a trend graphic that contains the meteorological data obtained by means of a meteorological station: global and diffuse radiations on a horizontal surface and ambient temperature. Based on those data and according to the expressions shown in [4] is

estimated the global radiation on the collectors surface (40° slope), as well as the horizontal radiation along the whole time period selected and the cloudiness index.

On the central part there are available different aspects of the installation to visualise, using tabs. The first one shows an array with all the data processed in the program, see Fig 1.

The next two tabs have the data corresponding to the solar collectors fields, the first for the evacuated tube collectors and the second for the flat plate ones. In each one of these tabs, there are three different charts (Fig 2):

The upper chart shows the evolution of the inlet and outlet temperatures as well as the flow throughout time.

The central chart shows the incident power on the field, estimated as the product of the radiation on the surface by the area. Here is also the power produced on the solar field. Using this previous data, with the quotient between them can be obtained the temporal evolution of the performance. Another represented curve is the theoretical performance that should be obtained on the field based on the manufacturer data.

In the chart of the bottom there is a comparison of the theoretical performance curve given by the manufacturer with the real one obtained from the collectors field. It is also made an estimation of the coefficients of the performance curve, using both lineal and quadratic approximation with the real performance curve.

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The next two tabs are related to the heat exchanger. On Fig 3 can be seen the behaviour of the heat exchanger of the flat collectors field. Again there are three charts: the upper one, shows the four temperatures and the two flows for primary and secondary along the time.

Fig 2. Trend charts for the Flat Collectors (31/08/2007)

Fig 3. Trend charts for the heat exchanger (31/0822007)

On the central chart, are shown the power on primary and secondary, and with it the instantaneous yield. Based on the temperature, it is determined la efficiency and the LMDT (Log Mean Temperature Difference). And finally the chart in the bottom represents the exchange coefficient, referred to the primary as well as to the secondary and the Capacity Coefficient.

The next tab is related to the storage tanks. It allows to see the evolution of temperatures on the top, bottom and middle of the tanks as well as the one in the room where them are situated. There has been designed two analogous charts, each one for one of the fields. By means of the difference between the values on the top and bottom of the tanks they can be represented the total stratification and the water temperature on the return of the installation. They are also shown the slope of each one of the curves. With this choosing a time period in which there is no activity on the tanks, the heat losses on each section can be estimated.

The next tab, called Hydraulic, shows the evolution of the pressures on the solar circuits. There are three charts. The one on he top, represents the flow on the solar primary and the looses of pressure of each one of the pumps, and this is used to calculate the hydraulic resistance throughout time. The central chart represents the pressure and la the hydraulic resistance, as a function of the flow. The lower chart represents the addition of the absolute pressure to the drop of pressure on the pumps.

On the second line of tabs the three first represent the evolution of the absorption chiller. The first shows the three basic circuits (Fig4): generator, evaporator and condenser. Each one of the charts contains the inlet and outlet temperatures, the flow and the power along the time whit regard to each circuit.

The second tab, (Fig 5) shows the evolution of the inlet and outlet temperatures on the loads circuit, as well as the demanded power. Also can be seen the evolution of the cold tank temperature and finally, the temperatures on the regulation valve of the condenser.

The third tab (Fig 6), represents the evolution of the temperatures on the generator valve. There is too a summarising chart with all the powers of the chiller. And finally, a chart with the COP using as a base the loads power or the evaporator power, as well as the load fractions for generator and evaporator.

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| Hidrauiic Energies

Fig 4. Absorption chiller’s generator, condenser and evaporator from 05:00 to 15:00 (13/08/2007)

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Fig 5: Absorption chiller’s load, cold storage and condenser valve from 05:00 to 15:00 (13/08/2007)

Fig 6. Generator valve, powers and performance from 05:00 to 15:00 (13/08/2007)

The next tab is Miscellaneus, in which two charts can be found: one with the more relevant operation temperatures and another with the averages calculated according to the methodology SACE [1]

The next tab, called Heat, shown a summary of the flows of the installation’s currents. Here can be seen the contributions that receives the absorption chiller and where do they come from: from the boiler or from the solar camp, and in this case, when is from the flat pate collectors, when from the evacuated tube collectors and when from both.

The last, shows the exploitation energetic balance for the installation during the calculation period established, in such way that can be seen for each one of the solar fields: energy incident, energy absorbed by the collectors, energy that reach the primary and the one that leaves the secondary on the heat exchangers, and accumulated energy. With all of those data, the calculation of the performance for collectors and heat exchangers is immediate. There is also done an estimation of the average powers using the working hours of each one of the circuits. Regarding to the chiller, is shown the energy of all of the four circuits (condenser, evaporator, generator and loads), the average powers during the working time and the average value of the temperatures SACE [1].

They are determined too the average COP using as a base the loads or the evaporator, as well as the solar fraction and the fractions for generator and evaporator.

2. Conclusions

To plan one installation, including a high level of instrumentation is fundamental in order to obtain enough information of the installation and its elements, being necessary as well to have tools to analyse it.

The program described in the present work, has made possible among others: to observe the evolution of the installation, detect malfunctioning, detect failures committed during the design and assembling of the installation and the identification of the different elements to be used on simulations.

For the future, it is expected to add new functionalities to the program, in order to obtain even more information.

References

[1] C. A. Balarasa, G. Grossmanb, H. M. Henningc, C. A. Infante, E. Podessere, L. Wangd, E. Wiemken,

Solar air conditioning in Europe—an overview, Renewable and Sustainable Energy Reviews, 11 (2007) 299-314

[2] J. Rodriguez, L. A. Bujedo, P. J. Martinez, Identification of real solar systems. Simulation parameters, ISES European Regional Conference, Eurosun’06, Glasgow, (2006).

[3] M. Poncela, J. I. Diaz, P. M. Caballero, L. A. Bujedo, Description del sistema de climatizacion solar por absorcion y de la red de monitorizacion y control del edificio de CARTIF. I Encuentro Iberoamericano de Refrigeracion y Aire Acondicionado, (2001)

[4] J. A. Duffie, W. A. Beckman, (1991). Solar engineering of thermal processes 2nd edition, John Wiley & Sons, New York.

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