NOVELTY - The system has a heat sink system (6) and associated connection systems (22, 24) comprising a heat exchanger system (36) coupled to a remote heat sink (37) containing working fluid and another heat exchanger system (42) coupled to ambient air as another heat sink. A fluid loop (10) interconnects a thermal system (2), the former and the latter heat exchanger system. A switchable valve mechanism selectively alters an order of the former and the latter heat exchanger system in relation to a fluid flow direction around the fluid loop. A controller (72) actuates the valve mechanism.    USE - Closed loop geothermal energy system i.e. commercial or industrial refrigeration system, for use in a supermarket.    ADVANTAGE - The system allows a role of an ambient air heat exchanger to be reversed to provide primary condensing in a summer mode and sub-cooling in a winter mode, thus improving the overall efficiency of the system. The heat sinks have different temperatures exploited to determine a desired mode of operation of the heat sink system so as to maximize cooling efficiency, minimize input energy and reduce the capital and running costs of the system. The system utilizes carbon dioxide as a refrigerant, and utilizes changes in seasonal ambient temperature relative to a remote heat sink to provide a selected combined cooling/condensation phase, thus increasing an annual operating efficiency of the system.    DETAILED DESCRIPTION - The latter heat exchanger system is a condenser, a gas cooler or a sub-cooler heat exchanger and an evaporator. The former heat exchanger system is a condensing heat exchanger such as shell-and-tube heat exchanger, plate heat exchanger or coaxial heat exchanger. The remote heat sink is a body of water, a mid aquifer, and an array or borehole heat exchangers. The thermal system is a commercial or industrial refrigeration system utilizing a vapor-compression Carnot cycle. An INDEPENDENT CLAIM is also included for a method for operating a thermal energy system.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a closed loop geothermal energy system.    Thermal system (2)    Heat sink system (6)    Fluid loop (10)    Associated connection systems (22, 24)    Heat exchanger systems (36, 42)    Remote heat sink (37)    Controller (72)