Abstract: A greenhouse and a method for controlling the environment of the interior space of the greenhouse is disclosed. The greenhouse (10) includes an interior insulative panel (22,23) and an exterior reflective panel (26) capable of insulating the interior of the greenhouse and reflecting sunlight into the interior. The greenhouse also includes a closed-system heat exchanger (30,31) having a plurality of spaced water-impermeable water flow passageways (60) through which water flows by gravitational forces and having a means for blowing air (65) between the water flow passageways (60) such that the air does not contact the water and such that the air is either heated or cooled by the water. In addition, the heat exchanger (30,31) may include a water discharge (71) and/or a gas discharge for the control of humidity and gas levels within the greenhouse.