An air conditioning assembly for an environmental chamber includes a suspended ceiling below a structural ceiling creating a plenum space. The suspended ceiling is configured to cover a substantially horizontal plane of the environmental chamber while leaving a first perimeter gap adjacent to a wall of the environmental chamber and a second perimeter gap adjacent to an opposing wall of the environmental chamber. A substantially vertical wall covers a vertical plane of the plenum space. At least one fan draws air from one from the environmental chamber into the plenum space through the first perimeter gap and blows air from the plenum space into the environmental chamber through the second perimeter gap. At least one air conditioning means in fluid communication with the at least one fan conditions the air flow passing through the at least one fan. The air conditioning assembly creates substantially laminar air flow.