With sufficient thermal storage capacity, it is feasible to meet all air-conditioning and heating requirements with a trivial fuel or electrical input in regions with hot summers and cold winters. Most buildings have available a large quantity of geologic material to satisfy the storage capacity needs, but the obstacle to using seasonal energy is an effective and inexpensive way to transfer heat to and from the soil.
Smart thermosiphon arrays (STAs) are a way to meet those thermal and economic benchmarks. STAs use standard passive thermosiphon mechanisms to transfer energy out of soil, and controlled rate transfer of energy into the soil using standard machinery. In this paper, we describe how STAs can provide seasonal energy storage to meet all climate control needs. The passive mode of soil freezing and the pump-assisted operation of air conditioning are modeled, and the resultant simulations are shown. When compared with conventional vertical borehole exchangers, simulations show the same total heat transfer can be obtained with 40% of the depth using STAs with drilling costs per length of borehole an order of magnitude lower.
Results of lab-scale smart thermosiphon experiments demonstrate uniform temperatures, and heat fluxes can be maintained on the inside wall of the thermosiphon pipe. This allows for dramatic enhancements of heat transfer rates. The first pilot-scale installation of smart thermosiphons for seasonal Underground Thermal Energy Storage (UTES) has demonstrated the ability to install the devices using inexpensive direct push techniques. Data indicate frozen ground in the subsurface.