Weather data

TRNSYS type 15-2 with weather data generated with Meteonorm 5.0 is used in the calculations. The weather data created with Meteonorm has been compared with reference years created based on a measurement period from 1992 to 2002. The amount of diffuse radiation is lower in the Meteonorm datafiles compared with the reference years. This is especially the case for Nuussuaq and Sisimiut. Further, the global radiation in the Meteonorm datafiles is higher than in the reference years. The direct radiation is therefore higher in the Meteonorm datafiles than the reference years.

2. Parameter variations

2.1. Collector tilt and orientation

Initial investigations are carried out with the validated models in order to determine the optimum tilt and orientation of the four solar collectors. The simulations are carried out with a constant mean solar collector fluid temperature of 60 °C during all operation hours of the year. The thermal performance of the collectors is investigated using the optimum tilt and orientation for each of the collectors. In Table 2 the values for the optimum tilt of the four solar collectors are given.

Table 2. Optimum tilt of the solar collectors. Table 3. Optimum orientation of the solar collectors.

Seido

5-8

Seido

1-8

Seido

10-20

Curved

Seido

10-20

Flat

Seido

5-8

Seido

1-8

Seido

10-20

Curved

Seido

10-20

Flat

Nuussuaq

75°

69°

76°

71°

Nuussuaq

-35°

-35°

-35°

-39°

Sisimiut

58°

58°

58°

55°

Sisimiut

12°

23°

10°

26°

Copenhagen

54°

51°

54°

52°

Copenhagen

Previous investigations have shown that the optimum tilt roughly follows the latitude. In this case that is true for Nuussuaq and Copenhagen. For Sisimiut the optimum tilt is somewhat lower than expected, this is because the amount of beam radiation is high. In Table 3 the optimum orientations of the four solar collectors are shown. In Nuussuaq the collectors are best situated turned 35° or 39° from south towards

east. In Sisimiut the collectors with the curved absorbers should be turned 10° or 12° from south towards west. The collectors with flat absorbers should be turned 23° or 26° towards west. In Copenhagen the collectors should be turned slightly from south towards west. The following analyses of the different parameters will use the optimum tilt and orientation for each of the four solar collectors according to the location simulated. In Fig 2 the thermal performance of the

 

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fluid temperature

 

Seido 5-8 —В— Seido 1-8

—9— Seido 10-20 with curved absorber —K— Seido 10-20 with flat absorber

 

Mean collector fluid temperature [ Cl

 

Fig 2. The thermal performance of the solar collectors in Nuussuaq using
optimum tilt and orientation.

 

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increasing solar collector fluid temperature faster in Nuussuaq than in Copenhagen. This is caused by

 

the cold climate in Nuussuaq. The mean solar collector fluid temperature used in the following

 

analyses is 60 °C.

 

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Distance between the center of the tubes [m]

 

image046image047

one glass tube to the neighbouring glass tube is reduced. Seido 10-20 with curved and flat absorber decreases more rapidly with an increase in the distance than Seido 5-8 and Seido 1-8. This is due to the larger numbers of glass tubes in the Seido 10-20 solar collectors than the Seido 5-8 and Seido 1-8. The increased centre distance will therefore result in a strongly increased length of the manifold. The

Подпись:optimum distance for each of the collectors at the different locations is shown in Table

3. The optimum tilts of the solar collectors are affected by a change in the glass tube centre distance. A change in the distance from the values given in Table 1 to the optimum distance values for the solar collectors located in Nuussuaq will result in an increase in the optimum tilt with up to 10°. For Sisimiut and Copenhagen a change in the distance from the values form Table 1 to the optimum values will only result in a small change in the optimum tilt, about 1-2°. The optimum orientation is also found for the optimum distance between the glass tubes. For the solar collectors located in Nuussuaq the optimum orientation is turned even more from south towards east, from about 35° to 65°. In Sisimiut a change in the centre distance of the glass tubes with the curved absorbers will result in a decrease in the optimum orientation from 12° and 10° to 2° and 5° from south towards west. The collectors with the flat absorbers located in Sisimiut have an increase in the optimum orientation from 23° and 26° to 37° and 36° from south towards west. In Copenhagen the optimum orientation changes only slightly with a change in the centre tube distance from about 2° to 5° from south towards west. An improvement of the centre distance between the glass tubes will only result in slight improvement of the thermal performance of the collectors with the flat fins at a mean collector fluid temperature of 60 °C. For the collectors with the curved fin the improvement of the thermal performance is in the range of 8-10 %, the largest improvement seen in Nuussuaq and the lowest seen in Copenhagen. Again a decrease in performance is seen for all the collectors at all three locations with a mean collector fluid temperature is 100 °C