Thermal energy storage and fire safety of building materials

Energy storage using organic phase change materials (PCMs) has attracted significant attention in recent years for renewable energy utilization in building materials. PCMs are capable of storing and releasing a large amount of latent heat during their phase transitions. Paraffin (PA), a eutectic mixture (EM) of capric acid (CA) and lauric acid (LA) and butyl stearate (BS) have been selected as PCMs for this work due to their melting temperatures being close to human comfort temperature, 17 - 28 oC. Plaster (PL) as a building material is chosen due to its ease of construction into plaster boards and also because it is a good insulator against heat and sound. The most significant concern when using an organic PCM is its flammability. This research sets out to determine the effect of using PCMs in PL on the product’s flammability, and whether it is possible to use carrier materials and/or flame retardants to reduce their flammability while maintaining the thermal energy storage properties. Three techniques of incorporation of PCMs into PL are used to address this question. The first one is to immerse PL into hot melted PCMs using a vacuum impregnation method. The PCM however, could easily leak to the surface of PL, particularly when the temperature is above the melting temperature of PCM and also their high flammability evaluated using cone calorimetry was a limiting factor to pursuance of this route. The second method is a direct incorporation technique, i.e. adding PCM directly to PL. With this method also the leakage of PCMs was observed and all samples ignited, though the flammability parameters were less intense than those observed when the immersion method was used. To prevent the leakage of PCM and to improve the consistency of organic PCM with building materials, form-stable PCMs composites are used in the third method. Carrier materials, namely nanoclay (NC), diatomaceous earth (DE), expanded perlite (EP), fly ash (FA) and brick dust (BD) were selected to adsorb and retain the PCMs in their pores. SEM (scanning electron microscope) demonstrated that PCMs were uniformly adsorbed in most of the carrier materials. DSC (differential scanning calorimeter) used to measure the thermal properties of PCMs showed that when these form stable composites were added to PL, they acted as PCMs, although the latent heat values were reduced. Thermal gravimetric analysis (TGA) results demonstrates that the PCMs’ decomposition was not affected by the presence of carrier materials or PL. Cone calorimetry showed that the use of carrier materials had minimal effect on the flammability of PCMs. To evaluate the thermal energy storage performance, a small environmental chamber was used, i.e. a small test “room” of PL with dimensions of 100 mm x 100 mm x 100 mm and thickness 10 mm was set up using 6 pieces of PL. The top board of the cubic room contained PCM, and the temperature differences between the surfaces of control PL and modified PL were recorded during heating and cooling of the room. The results from heating and cooling cycles showed that the PCMs and form stable-PCM composites reduced the peak temperature and delayed the time taken to release the stored energy, the values depending on the percentage of PCMs used. To reduce the flammability of PCMs while maintaining their energy storage performance, two approaches have been undertaken: (i) use of expanded graphite (EG) as a flame retardant carrier- material and (ii) use of a liquid flame-retardant, resorcinol bis(diphenyl phosphate) (RDP). The results demonstrated that the flame retardant did not affect the energy storage performance of the PCM. While RDP was not effective on a PA containing PL sample, the flammability of a PL+BS sample was significantly reduced with the addition of EG and RDP