Roof top gardens to conserve energy and use condensate from air conditioners productively -

Abstract

It is no secret to anyone living in Beirut in the summer that the city has become a concrete forest and an urban heat island. Old stone houses and gardens have been replaced by concrete towers and parking lots, in the name of development. The result is searing summer nights, a drastic loss of insect and avian biodiversity, and a large increase in energy usage for interior climate control. These problems are not restricted to Beirut but have rather been experienced in rapidly developing urban centers worldwide. Roof gardens can have a non-proportional effect on energy flux, especially if buildings are high and closely packed. The addition of plants and water retaining substrates to roof surfaces can lessen negative effects of buildings on local ecosystems and can reduce energy use. Rooftop gardens can also serve as social green space and urban gardens, as habitat for wildlife, help in local air-quality improvement, and reduce city heat-island effect. Moreover, if roof gardens are irrigated with non-traditional water sources such as air conditioner condensate, then they can be quite sustainable and environmentally friendly. In the present work I assessed the feasibility of building a roof garden on a bare flat roof in Beirut. The possibility of using recycled material as garden substrate was studied; the effect of roof gardens on temperature variations below the roof was evaluated; and finally I assessed whether enough water can be collected from air conditioner condensate to support a roof garden and whether the water is suitable for agriculture. Results suggest that rooftop gardens would be a great addition to the buildings of Beirut.