Air conditioning is the go-to method for dealing with hot summers in many parts of the American Southwest and Las Vegas is one of the hottest spots in America where other options can be tried. Daytime temperatures stay above the comfort level for months and the dry climate ensures that air conditioning becomes an expensive venture for homeowners. An experimental building in Las Vegas demonstrated in summer 2011 that water retained in an open roof pond could take care of much of the cooling requirement without air conditioning.
Roof ponds are an old concept: they have been investigated since the 1960s as a passive technique that makes use of the thermal mass characteristics of water, absorbing heat during the day and releasing it at night, a history later synthesized in a 2015 systematic review published in the journal Applied Energy. Separately, the 2011 Las Vegas experiment made a direct comparison between dry and wet roof ponds and indicated the level of shortfalls of each in terms of comfort.
