Thermal characteristics of a long-term heat storage unit with sodium acetate trihydrate

Energy storage is a key technology to provide stable renewable energy supply to buildings. Latent heat energy storage system is a promising technique for domestic thermal energy storage systems due to its high thermal energy storage density and the ability to store heat for both short and long periods. The common domestic heat storage accumulators are designed for short-term storage, where heat can't be stored for a long time. In this experiment investigation, a latent heat storage with 75 L water and 137.8 kg phase change material is tested. Sodium acetate trihydrate based composite with stable supercooling ability is used as the phase change material. The sensible heat of the storage is used for short-term heat storage, the latent heat is for long-term heat storage. The combination of short-term heat storage and long-term heat storage is attractive for heating systems with variable heat supply. In this experiment, thermal power and heat exchange capacity rates of the heat storage were analyzed. The stable supercooling success rate and hence the long-term heat storage was also investigated. The results showed that, under the test conditions, 21.7 kWh heat was stored in the tank during charging, 14.0 kWh heat was released during discharging of the sensible heat (short-term heat storage) and 7.6 kWh heat was discharged during discharging of the latent heat (long-term heat storage). The sodium acetate trihydrate remained stable supercooled in 66% of the test cycles. The storage had a relatively high heat exchange capacity rate of at least 340 W/K during charging.