Passive Cooling Against the (Night) Sky

This paper summarises R&D work that evolved towards the design of a smart skylight (roof window) aiming at keeping its inside compartment at a lower temperature than the surroundings. A skylight that gives maximum cooling (summer) or insulating (winter) performance is being optimised at Åbo Akademi University for conditions in (northern) Europe. As passive cooling through long-wave (LW) thermal radiation must counteract incoming short-wave (SW) thermal radiation, a drawback to that region is the length of daytime during summer. For equatorial locations like Kenya the use of a passive cooling skylight would benefit from the more constant duration of night-time and temperature. Depending on location for application, a two- or morewindowed skylight must be designed. Results presented include the modelling of skylight windows using a four-band thermal radiation model and Comsol Multiphysics software for simulation. Several cases show that very significant increases in (passive) cooling heat output can be achieved.