Assessment of Building Thermal Performance With Roof Top Greenery System and Bio-Phase Change Materials in the Australian Sub-Tropical Climate

The incorporation of extensive rooftop greenery and bio-phase change materials as building envelopes in subtropical climates has enormous potential to counteract the adverse effects of escalating energy consumption and greenhouse gas emissions. These envelopes are capable of limiting the heat gain, reducing the cooling energy, promoting thermal comfort, and shifting the peak load throughout the day. Its design and effectiveness may differ significantly depending on location and weather. This study investigates the effects of an extensive rooftop greenery system (RTGS) and bio-phase change materials (bio-PCMs) on the thermal performance and energy consumption of buildings in the subtropical climate of Australia. Two identical shipping containers were used as experimental buildings (replicas of small offices), one equipped with RTGS and bio-PCM, whereas the other lacked this feature, that is, a reference bare roof (BR). The experimental investigations were conducted from 3rd September to 8 October 2024. While considering a typical day within the experiment duration, the data showed a temperature difference of approximately <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$7^{\circ} \mathrm{C}$</tex> and humidity difference of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 5 \%}$</tex> at approximately 11 am of that day. It was found from the experimental results that buildings with RTGS and bio-PCM as envelopes can save approximately 26.49 % of energy in a typical week in September 2024, with a maximum energy saving of up to 32 % experienced on a typical day. In terms of thermal comfort, the RTGS with bio-PCM maintained stable temperature and humidity levels that were favourable to standard ideal comfort zone conditions.