The table shows some properties of two media used for thermal energy storage to conserve heat in green building designs.
| Storage Medium | Primary Source | Heat Storage Characteristic | Environmental & Safety Properties |
|---|---|---|---|
| Water | Abundant, local natural resource | Sensible heat capacity: 4.18 kJ kg-1 K-1 | Non-toxic, non-flammable, risk of leakage causing structural damage; expands and freezes below 0 ∘C0\,^{\circ}\text{C}0∘C |
| Paraffin Wax (PCM) | Crude oil refining byproduct | Latent heat of fusion: 190 kJ kg-1 (melts and solidifies at 22 ∘C22\,^{\circ}\text{C}22∘C) | Highly flammable, potential skin irritant, non-biodegradable |
A designer wants to install a thermal buffer in a greenhouse to absorb excess solar energy during the day and release it at night to maintain a steady ambient temperature of around 18 ∘C18\,^{\circ}\text{C}18∘C to 25 ∘C25\,^{\circ}\text{C}25∘C.
Assess which of these materials is more suitable to use as the thermal energy storage medium for this greenhouse.
Your answer should compare their energy storage and transfer performance, the sustainability of their raw materials, and their safety/operational risks.