Sodium acetate-urea composite phase change material used in building envelopes for thermal insulation

Integrating phase change material with building envelopes is an effective way to reduce cooling or heating loads, improve indoor thermal comfort and save building energy consumption. In this paper, the composite phase change material of sodium acetate and urea is prepared and its thermal-physical properties with different mixing mass ratios are investigated through experiment and T-history method. Moreover, the heat transfer model of building envelopes with phase change material is established and different phase change material locations in external walls for thermal insulation are compared based on integrated uncomfortable degree. The results show that (1) with rising urea mass fraction, both phase change temperature and latent fusion heat (enthalpy) decline; (2) strontium sulfate is an effective nucleating additive to decrease super-cooling degree for such phase change material solidification and (3) to improve indoor thermal comfort, it is preferable to put phase change material in the middle of external walls. Furthermore, the illustrative example of an office building in Chengdu indicates that phase change material insulation can lead to time lag and decrement for indoor air temperature variations. It also indicates that after inserting such phase change material into building external wall, the highest indoor temperature can be decreased by 7 degrees C, leading to 60% cooling energy saving in one typical summer day. This work can provide guidance for building thermal design with phase change materials. Practical application: The studied sodium acetate-urea composite phase change material has been used as energy storage and thermal insulation materials inserted in envelopes for the demonstration project of low/zero energy consumption passive buildings in China.