Development of a building-integrated roof top greenhouse in Barcelona, Spain

Urban horticulture has intensified in recent years. The trend has resulted from a growing interest in the development of new agricultural spaces in urban areas. In this regard, the Integrated Roof Top Greenhouse concept (I-RTG) is based on the construction of RTGs with interchange of residual energy (heating/cooling), water and CO₂ fluxes between the greenhouse and the associated building. With such greenhouse system, potential benefits from environmental, economic and social points of view can be achieved. In 2014, a research-oriented roof top greenhouse was constructed on top of the building that hosts the Institute of Environmental Science and Technology (ICTA Universitat Autonoma of Barcelona, Spain). It is called the RTG-Lab. Floor surface is 122.8 m². It is a two-span, sloped-roof metal structure covered with single-layer polycarbonate sheets. The first crop (lettuce) was planted in perlite bags on September 2014. Currently a tomato crop is growing in the greenhouse. This article presents the first evaluation of the RTG Lab in terms of climate performance. In contrast with conventional greenhouses, thermal inertia of construction elements in the RTG Lab (viz. the concrete floor) made a significant contribution to the night-time greenhouse temperature. The RTG Lab also benefited from the air exchange with the associated building, particularly at night. Additionally some waste heat from the building climate equipment made it possible keeping the greenhouse temperature at favourable conditions without using any additional heating. Some peculiarities of the RTG Lab, such as the different wind regime in comparison with conventional greenhouses are also discussed.