Radiative cooling in Northern Europe using a roof window

The design and performance of a triple glass window used as a roof component was analyzed in this paper. A mathematical model was set up for the component and weather data for the Finnish city Helsinki was used to assess its performance. This roof component would act as a passive radiative cooler during the summer and as a thermal insulator during the rest of the year. This versatile usage of the window component would thus decrease the need for traditional air-conditioning during summer and hence save electricity. The triple glass window would consist of one normal silica window and of two High Density Polyethylene (HPDE) windows. The space between the three windows would contain a (pressurized) greenhouse gas that would act as the heat carrier in this system. The heat would be transferred in to the system to the gas by heat radiation, conduction and natural convection through the window facing the room. This heated gas would then rise to the upper vacant space due to a decrease in the gases density caused by the heating. In the upper vacant part, the gas would then be cooled by radiative cooling through the HDPE, and the atmospheric window with colder air masses in the upper atmosphere. When, the greenhouse gas would have cooled down its density would increase and the gas would drop to the lower part of the window component. During times when no cooling would be needed the connection between the two vacant spaces would be cut, thus changing the roof components' task from a passive radiative cooler to a thermal insulator. The heating of the space due to sunshine is of course evident and lower temperatures would be achieved if no window at all be used, but for places were roof windows are built this component would offer a viable alternative. This paper is a continuation to the paper by Zevenhoven and Fält submitted to this conference (1).