Abstract
In the conventional system, heat is recovered as sensible heat through liquid anti-freezer circulating in a piping laid underground, but if CO2 is used as a heat transfer fluid, heat is recovered as latent heat which increases the capacity and enables to promote downsize of the equipment and reduction of the electric consumption. Our last report showed that the CO2-system exerted the same heating ability with the propylene-glycol system with a half length of heat recovery piping and a half electric consumption of the propylene-glycol system. And the reduction in the diameter of the CO2 recovery piping was possible to 50 mm at most to gain more than adequate heating effect. In this study, CO2 spiral recovery piping was installed in shallow soil of 4 m depth for the further cost reduction. And latent heat of CO2 was utilized for cooling. As a result, adequate heating ability was derived from shallow soil of 4 m depth. And cooling operation, which need CO2 forced circulating with in-line pump, was competitive in ability and electric consumption.
