Model-RT is an air to water heat pump, designed specifically to be installed in attics or in the structure of a building.  It was created around the idea of making a heat pump accessible to viennese Altbau apartments without having renovations be done to the building.  The heat pump is stored in the attic where it gets air in and out through a vent in the chimney.  The hot water is then brought down to the taps and radiators of the apartments by pipes through the bottom part of the chimney.