Rooftop plant factories: effects on energy use for heating, cooling and electric lighting

Abstract: Within the next thirty years, two thirds of the human population will live in a city. This growing urban population requires a major shift in the way we produce and distribute food, since industrial agriculture practices contribute to climate change, biodiversity losses, pollution of waterways, soil degradation, etc. Urban and peri-urban agriculture and forestry (UPAF) represent one of the strategies that can contribute to climate mitigation, adaptation and development. Amongst the urban farming (UF) systems, rooftop plant factories may provide part of the solution for vegetable and fruit production in the city, while solving current problems created by existing flat roofs and saving on arable land outside the city. This thesis presents a study of rooftop greenhouse (RTG) located on a typical warehouse in Malmö, Sweden (lat. 55.6°N, long. 13.0°E). The goal of the study was to investigate the effect on energy use of building a greenhouse on the roof of an existing warehouse. The study was performed by dynamic energy simulations with the computer program IDA-ICE. The results show that adding the RTG on the warehouse reduces total energy use compared to greenhouse and warehouse as stand-alone structures. Furthermore, the results indicate that the glazing and shading solutions are important aspects determining the energy-efficiency of the integrated system. The energy use for electric lighting is also significantly reduced by the RTG compared to an indoor horizontal farm of similar size illuminated by LED lamps. The main conclusion is that RTGs offer a great potential for food production in the city with the additional benefit of reducing overall energy use of host building and greenhouse. RTGs are also more energy-efficient than indoor farms illuminated by LEDs, when considering all energy end-uses (heating, cooling, lighting, and ventilation).