Using rocks as a heat sink

A scientific paper concludes:

Abstract

A study was conducted to store solar energy in an underground rock-bed for greenhouse heating. Experiments were carried out in two identical polyethylene tunnel type greenhouses, each with 15 m[2] ground area. Rocks were filled in two canals excavated and insulated in the soil of one of the greenhouses. Greenhouse air was pushed through the rock-bed by a centrifugal fan with 1100 m[3]/h air flow rate and controlled by two thermostats when the energy storage or release was required. No crops were grown in the greenhouses and the vents were kept closed unless excessive condensation occurrence inside the greenhouses. The results of this study showed that the rock-bed system created an air temperature difference of about 10 °C at night, between the two greenhouses, the control one having the lower temperature. Furthermore, the rock-bed system kept the inside air temperature higher than that of outside air at night, even in an overcast day following a clear day. Whilst solar energy collection efficiency of the system was 34%, its energy recovery or release efficiency was higher than 80%. A numerical mathematical model considered here represented actual data well. An economic analysis indicated that the rock-bed system is more economical than the LPG or petroleum-based fuel burning heating systems widely used in Turkish greenhouses.

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