Experimental Investigation on the Stability of Biocomposite Phase Change Materials for Building Applications

Abstract

According to International Energy Agency, active space cooling and air conditioning systems are essential to maintain indoor thermal comfort, which consumes approximately 16% of the building sector’s final electricity consumption and contributes 3.94% of global greenhouse gas emissions. In this regard, low-cost but effective passive solutions have immense potential to improve operational energy efficiency in the building sector. The use of organic phase change materials (PCM) on building envelope can provide high thermal mass and thus can lower the temperature fluctuation inside the building. Porous biochar has been used as a matrix to compensate for the low leakage stability and low thermal conductivity of available PCM (OM35). The biochar has been obtained through pyrolysis of water hyacinth and co-pyrolysis of water hyacinth (W), sugarcane bagasse (S), and yellow oleander (Y) at a temperature of 550°C, for a holding time of 1 h and at a heating rate of 10°C/min in Argon environment at a fixed bed batch reactor. Two biocomposite PCMs, namely, W-PCM and T₀_SWY-PCM, are made through simple impregnation method. The durability and dependability of the developed biocomposite PCMs need to be studied before applying them to building envelopes. In the current study, W-PCM and T₀_SWY-PCM are studied for the change of thermal, physical, and chemical properties after performing thermal cycling tests and compared with OM35. The material has been subjected to simultaneous heating and cooling cycles in a developed thermal cycling chamber within a temperature range of 25–45°C. The temperature inside the insulated chamber is maintained with the help of a tubular air heater (500W), eight Peltier cooling elements (12 V, 60 W), and two Subzero temperature controllers (SZ7569). The samples have been tested for leakage, chemical, and thermal stability after the completion of 50,100,150 and 200 thermal cycles, respectively. The FTIR and XRD analyses confirm that no significant changes occur in the functional groups for both the biocomposite PCMs after completing 200 thermal cycles. Also, the leakage stability of the two biocomposite PCMs has been ensured through the leakage stability test on filter paper (Whatman Grad 1, 11 µm size). The DSC results showed that there is a reduction of 0.25% and 2.58% in melting point and heat of fusion, respectively, after 200 cycles for W-PCM. The negligible changes in physical, thermal, and chemical properties over the thermal cycles confirm that W-PCM is a good option to be used as thermal energy storage material in building envelopes.