Supercooling stability of sodium acetate trihydrate composites in multiple heat storage units.

Keeping sodium acetate trihydrate (SAT) in supercooled state can be utilized to store heat loss free over long periods. The main risk with this technology is that the SAT may crystalize spontaneously and release the stored heat before desired. A test rig with 10 marketed heat storage units with water and 35 kg sodium acetate trihydrate composite was built and multiple heating and cooling cycles were carried out with the units. It was monitored if the sodium acetate trihydrate remained supercooled in the 3 days storage period or if the solidification started spontaneously. The units were charged with an inlet temperature of 87°C, and then discharged with inlet temperatures of 14°C, 22°C, 28°C or 35°C. Spontaneous solidifications occurred more frequently during discharge in the test cycles with lower discharge temperatures compared to higher inlet temperatures.