Integrated rooftop greenhouses: Energy efficiency of buildings metabolism for local food production

IntroductionAt present, urban agriculture is an increasingly integrated element into the metabolism of cities promoting sustainability. Rooftop Greenhouses (RTGs) are greenhouses implemented on urban buildings that promote... [ view full abstract ]

Introduction

At present, urban agriculture is an increasingly integrated element into the metabolism of cities promoting sustainability. Rooftop Greenhouses (RTGs) are greenhouses implemented on urban buildings that promote local food production, usually through soil-less culture systems. RTGs are an alternative for creating new agricultural spaces in cities through multifunctionality and giving new uses to spaces currently little valued.

In this sense, Fertilecity research project, analyzes a new agricultural production system for Mediterranean urban areas through the integration of greenhouses on the rooftop of buildings. The ICTA Integrated Rooftop Greenhouse (ICTA-iRTG), located on the rooftop of the ICTA-ICP building (UAB-campus, Bellaterra, Spain), will be used for this purpose. ICTA-iRTG takes advantage of the energy, water and CO₂ residual flows in the metabolism of the building for food production. This contribution reports the 2015 annual temperature performance of the ICTA-iRTG, quantifyes the heating energy that iRTG has passively and actively recycled from the ICTA-ICP, and summarizes the reduced environmental impacts resulting.

Methods

Sensor systems facilitate the operation and monitoring of temperature data in the building and ICTA-iRTG, in terms of temperature, energy and other climatic variables. The monitoring design consists of instruments uniformly distributed inside the RTG and other spaces of the building rooftop level. Measurements are taken every 5 seconds and an average is done every 10 minutes. Besides, ICTA-iRTG was modelled in EnergyPlus software as a freestanding structure using detailed thermophysical-properties, weather-data, control-strategies and dynamic-temperatures.

Results

ICTA-iRTG has better average temperatures (16.5-25.79°C) than a freestanding greenhouse in Mediterranean area, allowing a production of 16.2kg/m² of tomato and 1.86kg/m² of lettuces. To recreate ICTA-iRTG’s temperatures, a freestanding structure would have required 341.93kWh/m²/yr of heating load. It has been estimated that ICTA-iRTG has offered net carbon savings of 113.8kg.CO₂(eq)/m²/yr and economic savings of 19.63€/m²/yr.

Discussion and conclusions

Energy and thermal metabolism of ICTA-iRTG maintains ideal conditions for crop-growth all year and it offers a thermal advantage in winter compared to freestanding greenhouses. iRTG concept is an alternative to currently unused urban roofs by creating new agricultural spaces, and increasing urban food security, saving energy and money, reducing CO₂ emissions and adding eco-innovation in cities and food industry.