Divided storage in an indirect integral collector storage with immersed heat exchanger

Experiments are presented to demonstrate the benefit of dividing an indirect integral collector storage into two storage compartments. Transient discharge experiments were conducted in an undivided and equally divided 126 liter rectangular storage vessel with a height to depth aspect ratio of 9.3:1 and inclined at 30 degrees. A 240-tube copper heat exchanger with a total surface area of 2.38 m² was immersed in the storage fluid. For the divided storage, the tube-side flow path was in series through the two compartments. Water flow rate through the heat exchanger was varied from 0.05 to 0.15 kg/s to demonstrate the effect of the number of transfer units (NTU) on comparative performance of undivided and divided storage vessels. Reported measurements include transient storage temperature distribution, heat exchanger outlet temperature, and delivered energy of the divided and undivided storage. Results are generally in agreement with a prior analytical model. The divided storage provides higher heat exchanger outlet temperatures during most of the discharge and higher cumulative delivered energy. The benefit increases with increasing NTU. For a flow rate of 0.05 kg/s, corresponding to a nominal NTU of 7, the divided storage delivers approximately 11% more energy than the undivided storage when 126 liters of hot water, representing 76% of the stored energy, has been delivered.