In solar-heated buildings, energy is often stored as sensible heat in rocks, concrete, or water during the day for use at night. To minimize the storage space, it is desirable to use a material that can store a large amount of heat while experiencing a small temperature change. A large amount of heat can be stored essentially at constant temperature during phase-change process, and thus materials that change phase at about room temperature such as glaubers salt (sodium sulfate decahydrate), which has a melting point of 32°C and a heat of fusion of 329 kJ/L, are very suitable for this purpose.

a) Determine how much heat can be stored in a 4-m3 storage space using glaubers salt undergoing a phase change.

b) Determine how much heat can be stored in a 4-m3 storage space using granite rocks with a heat capacity of 2.32 kJ/kg·°C and a temperature change of 20°C. The density of granite is 2700 kg/m3.

c) Determine how much heat can be stored in a 4-m3 storage space using water with a heat capacity of 4.0 kJ/kg·°C and a temperature change of 20°C. The density of water is 1000 kg/m3.