Experimental investigations of multiple heat storage units utilizing supercooling of sodium acetate trihydrate: Stability in application size units

Stable supercooling of sodium acetate trihydrate (SAT) composites can be used to store heat over long periods. When the melted SAT is supercooled and in temperature equilibrium with the ambient, the latent heat of fusion is essentially stored without further heat loss. The main limitation of this technology is that the supercooled SAT may crystalize spontaneously and release the stored heat before desired if the storage design does not allow for the principle to work. These investigations elucidate the effects of charge and discharge temperatures and durations on the stability of the supercooling in storage units designed for domestic hot water application. A test rig with 10 identical heat storage units with water and 35 kg sodium acetate trihydrate composite was set up. Multiple heating and cooling cycles were carried out with charge temperatures between 84 degrees C and 94 degrees C for various durations and with discharge temperatures from 10 degrees C to 35 degrees C. The investigations showed that charging the storage units with an inlet temperature of 89 or 92 degrees C resulted in the highest occurrences of stable supercooling. Discharging with inlet temperatures of 10 degrees C resulted in higher occurrence of spontaneous solidification during discharge compared to higher inlet temperatures. There was a large deviation in how each tank performed. The best performing tank achieved stable supercooling in 87 % of the test cycles and the worst performing tank achieved stable supercooling in 30 % of the test cycles.