5. Annual performance of water-in-glass solar water heaters
5.1. Comparison of different system configurations
The performance of a selective flat plate system and two
configurations of water-in-glass systems with 30 tube,
2.9 m2 collector array at 22 inclination and 220-L tank
operating in Sydney are compared in Fig. 5. The flat plate
system has an annual energy savings of 77%, the singletank
evacuated tube system has an annual saving of
70.9% and evacuated tube solar pre-heater with a boost
tank has a savings of 66.2%. Flat-plate collectors usually
benefit from separating the solar tank and the boost tank
which results in improved stratification and as a result
increased collector efficiency. This study shows that
although operating at lower temperatures due to a larger
solar volume, the performance of the pre-heater evacuated
tube system with a separate boost tank is lower than the
single-tank system. This is because the heat loss from evacuated
tube collectors is small and the additional heat loss
from the boost tank outweighs the advantage of having
the collector operating at a lower temperature.