The annual results for this system are shown in Table 6. As the characteristics of all systems are the same, the inlet temperature depends on the heating load which affects the temperature of the stored water and thus the temperature of the water entering the solar collector (from the bottom of the storage tank).

This behaviour is illustrated in the comparative graphs of the monthly useful energy (Qu) and auxiliary energy (Qaux) for the four types of collectors considered shown in Figs 4 and 5 for Nicosia and Athens respectively. As can be seen in both cases the performance (Qu) of the collectors during summertime is lower than that of other mid-season months (March and October). No auxiliary is required during the period April to November.

2.1 Industrial Process Heat System

The annual results for this system are shown in Table 7. Typical monthly results for type A collectors for both Nicosia and Athens are shown in Table 8.

Comparative graphs of the monthly useful energy (Qu) and auxiliary energy (Qaux) for the four types of collectors considered are shown in Figs 6 and 7 for Nicosia and Athens respectively. As can be seen again the performance of the color collectors is somewhat lower than that of the black colored collectors. The difference in performance between the respective cases is almost constant in all months of the year. The maximum useful energy collected occurs in both locations during the month of August and is about 71 GJ and 73 GJ (black selective absorber) for Nicosia and Athens respectively.

It can be generally concluded from the results presented in this section that color collectors give in most of the cases about 10% lower performance than collectors painted with black paint either for the normal paint or selective. This means that 10% more collector area would be required to obtain the same performance as the black colored collectors, which is acceptable.

3. CONCLUSIONS

In this paper applications of solar collectors with colored absorbers in a house heating, multi-flat residential or office buildings, and industrial process heat applications are
presented. These systems are simulated on an annual basis at two different locations at different latitudes, Nicosia, Cyprus (35°) and Athens, Greece (38°).

The results show that although the colored collectors present lower efficiency than the typical black type collectors, the difference in energy output depends on the absorber darkness. For a medium value of the coefficient of absorptance (a=0.85), the colored collectors give satisfactory results regarding the drop of the amount of collected energy for the two locations (about 10%), compared to collectors with black absorbers (a=0.95).

This implies the use of proportionate larger collector aperture area to have the same energy output as that of typical black colored collectors.

REFERENCES

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