THE FERTILECITY IN BARCELONA, OPERATED BY UAB (SPAIN)

By Maeva Sabre (CSTB)

Building-integrated-rooftop-greenhouses-

Pilot Id

The building was new, the 245-m² greenhouse was built in 2012-2013, and production started in 2014. UB was the architect and the founder. The main purpose of the top floor greenhouse was research.
The main activities are plant production, visits, training, research, and vegetable (tomatoes, herbs) cultivation.

Business – value creation

The main activity of the greenhouse (and of the building too) is research. Because of this there is no specific business model as there would be in conventional farming targeting profitable production.

Construction

The building is 16 meters high, and composed of two basements, 3 floors, and an RTG. The height of the building including the greenhouse is 20 meters. The structure is made of reinforced concrete on pillars and post-tensioned slabs. The total roof surface is 1,180 m², with 245 m² dedicated to the greenhouse and 935 m² dedicated to other uses.

It was designed according to national standards, i.e. the Spanish construction code “Codigo técnico de la Edification” and other regulations of the public code and educational code. The roof was initially designed to receive a greenhouse

  • Permanent Load: 2.5 kN/m²

  • Exploitation overload: 4.5 kN/m²

  • Snow overload: 0.4 kN/m²

  • Wind load: 0.5 kN/m²

The roof covering is composed of an asphalt layer adhering to the concrete slab + an inverted insulation layer + a heavy protection made of 10 cm of a thick water-repellent concrete pavement.

The evacuation system is based on gravity, and rainwater is collected from the entire roof.

Other neighbouring roofs are connected to the rainwater harvesting system. In total, an area of about 1,900 m² is used for collecting rainwater. The capacity of the tank is 100 m³ with additional room, and 35 m³ for ultra-filtered water. This system reduces water consumption by 18%.

The greenhouse is 4 meters high.

The frame is made of steel. Facades are made of corrugated polycarbonate sheets whose opening and closing can be monitored for ventilation.

The connection to the greenhouse and to the exterior can be regulated through polyethylene film curtains that can be rolled up and down by an automated system.

Energy management

The building is an example of a fully integrated RTG. It produces heat, CO² and rainwater, i.e. ideal conditions for plant growth. The average temperatures are 16.5 ºC in winter and 25.79 ºC summer (2015 data).
Due to thermal inertia and waste heat, an additional heating system is not necessary, so that the integrated greenhouse recycles 341.93 kWh/m²·yr from the main building. This recycled energy amounts to CO² and cost savings (113.8 CO² (eq)/m²·yr and 19.63 €/m²·yr compared with an oil-heated freestanding greenhouse) (A. Nadal et al., 2017).
The vents are managed by an automatic control system. The CO²-loaded waste air from working areas in the building is recirculated to the greenhouse for carbon fertilisation.
Greenhouse conditions and outdoor conditions are monitored. Based on this data, the heat demand of the greenhouse can be calculated. The heat itself is supplied by a geothermal system that reaches about 100 m into the ground. In the cold season, the greenhouse air is kept above a temperature of 14°C thanks to the connection to the building. This leads to energy savings of 390 kWh/m²*yr.
Finally, thermal screens are also used as energy savers.

Production

The greenhouse has a total surface of 245 m². However, only part of its surface is dedicated to crops. There is a 75-m² area for tomatoes and another 75-m² area for other crops with shorter growth cycles (leafy greens, spinach, chard, etc.).

It uses a hydroponic system with perlite as a growing media. The crops are irrigated with collected rainwater. The water is collected from the ICTA building (approx. 1,600 m²) and from the roof of the neighbouring EUREKA building (approx. 500 m²), and is accumulated in two tanks, a 100-m³ tank for irrigation water and another 35-m³ tank for ultra-filtered water.

The main activity of the greenhouse (and of the building too) is research. The harvested vegetables are shared among the building users or used in the common dining area.

Herb production runs all year round. Tomatoes are not cultivated during the coldest winter period. The tomato area produces 1,660 kg yearly.

These activities also generate waste:

  • 300 kg of plant biomass residues generated during the production season and at the end of it

  • 30 kg of growing media are lost in the cropping process

  • 30 kg of plastic waste.