Disclosed herein is a solar thermal collector system that is particularly configured for dual use as a radiant cooling system. In accordance with aspects of a particular embodiment of the invention, the solar thermal collector system includes a solar thermal module having a glazing sheet at a top, exterior surface, and an absorber sheet within the module positioned below and spaced apart from the glazing sheet. The absorber sheet and the glazing sheet are fluidly connected to a fluid handling system, and are configured to carry a working fluid that may be heated in the absorber sheet by the sun to transfer such heat to equipment within the facility in which the system is installed, and to carry the working fluid through the glazing sheet to transfer heat collected from the facility to space. The solar thermal collector module is preferably provided a thermally actuated valve that allows the working fluid to also flow through the glazing sheet, which results in self-regulation of the temperature of the module below a critical design temperature.