Thermal Mass

Effectiveness of Materials for Seasonal Heat Storage

Water is the most robust, bulk heat storage medium, 5x the specific heat capacity of rock - and 2.5 the heat capacity by volume since rock is more dense than water (rocks sink).

A practical storage medium could thus be rock/water mix, where the water has good heat exchange qualities. This is for seasonal storage.

Notes

• 830J/kgC specific heat of sand.
• 830kJ/tonC. Assume a 140 to 90F drop, or 30C.
• 25,000kJ/ton30C
• 25MJ/ton of storage for normal conditions.
• Sand weighs 1.3 ton/cubic yard
• 32 MJ/yard
• Wood is 16MJ/kg
• Equivalent heat of 2 kg of wood
• 3 cubic yards are 6 kg of wood.
• Conductivity of sand - .25W/MK.
• 4.186J/gC° specific heat of water.