The storage of solar heat in the earth beneath a building, using an air flow gravel bed heat exchanger to supply a heat pump, is analyzed. A simulation of annual performance is demonstrated, using a transient analysis to model heat flow ambients to and from the gravel bed, combined with iterative steady state approximations for the more slowly varying heat losses through the large thermal mass of soil. A cost analysis example is solved.
Gravel bed heat exchangers are one means to provide large (seasonal) heat storage capacity for solar installations in new buildings at relatively low cost and without added space requirements.