EuroSun2008-5

Determination of Daily System Performance

As for determination of daily system performance, the system shall be allowed to operate for 12 h, from 6 h before solar noon until 6 h after solar noon. At 6 h after solar noon the collector shall be shielded, and water drawn off from the store at a constant flow rate of 600 lit/hr. The cold make-up water shall be at the temperature tmain defined during the preconditioning of the system. The temperature of the water being drawn off (td) shall be measured at least every 15 s and an average value recorded at least every time a tenth of the tank volume is drawn off. A volume of water equal to three times the tank volume shall be drawn off. If the temperature difference between the water drawn off and the cold water entering the store is greater than 1 K after three tank volumes, then the draw-off shall be continued until the temperature difference is less than 1K. And especially during the draw-off,

the temperature of the cold water entering the storage tank shall not fluctuate by more than ±0.25 K

and shall not drift by more than 0.2 K during the draw-off period. The flow rate during the draw-off of hot water from the store is very important, and can greatly influence the draw-off temperature profile. The flow controller must therefore maintain a constant flow rate through the storage vessel at 600lit/hr

±50lit/hr.

Figs. 5-7 present the main experimental results gained by the automatic system. Daily draw-off performance, inlet temperature and flow rate profiles can be seen in Fig. 5. And the Fig. 6 shows that the temperature difference between outlet temperature and inlet temperature of system is suitable to the requirements of the standard. From Fig. 7 the fluctuation and drift of the temperature of the entering the storage tank during the preconditioning period and drawn-off period separately can be seen.