The Research Centre in Urban farming of Liège University is developing a 198-m² (5.5 * 36 m) RTG in its Gembloux centre (Belgium). The greenhouse will be inserted on the rooftop of a modern building of the agriculture faculty of Liège University – Gembloux Agro-Bio Tech faculty.
The research centre in Urban Agriculture is dedicated to the development of research and tools for farming adapted to urban environments. This includes both low-tech and high-tech approaches, such as SPIN, agroforestry, aquaponics, rooftop farming and indoor cultivation. Therefore, the RTG will complete an ecosystem of research infrastructures, including experimental fields, aquaponics systems and container systems.
The RTG will be dedicated to research associated with the production systems adapted to rooftop farming. Besides, the greenhouse will also host educational activities and demonstrations of innovative plant production systems.
Business – value creation
The aim of the greenhouse is to reinforce the research infrastructures of the Research Centre in Urban Farming of Liège University.
The economic model of a research centre is generally based on public funding. Public financers generally evaluate the project based on the experience of the research centre and its ability to carry out research. Research greenhouses will enable the research centre to gather more experience and to host future experiments. In fine, this will open onto new types of funding for the research centre.
The Research Centre in Urban Farming will sell its expertise to private companies. The greenhouse will be used to carry out experiments for external companies, e.g. evaluating production systems, fertilisers, or other types of products.
The TERRA building was designed to host urban farming activities. The roof has a high bearing capacity (4.5 KN/m²). Nevertheless, although the building can accept high loads, it cannot withstand lifting forces, such as the forces exerted by the wind on the greenhouse. Therefore, the greenhouse structure needs to be heavy enough to avoid any lifting force. This implies that even with the heaviest greenhouse material present on the market (safety glass), the greenhouse needs to be loaded.
The roof is covered by a 20 cm insulation layer made of polyisocyanurate foam and a waterproofing layer made of plastomer (APP) bitumen. These materials can handle relatively high pressures: a long-term pressure of 60 KN/m² results in a 1 mm deformation of the insulation layer. Insulation and waterproofing resistance are not a limiting factor in the construction of the greenhouse. Besides, the anchoring of the greenhouse in the building would require drilling through the insulation and waterproofing layer. This is quite expensive and raises questions as to insurance. Therefore, the greenhouse will not be anchored in the building, but simply laid down on the roof.
The greenhouse structure will be based on pillars with aluminium profiles spaced out every 6 m, which is the standard distance in greenhouse construction. These pillars will be inserted into a concrete structure laid down on the roof. The maximum forces exerted by the pillars on the concrete structure will range from -6 to 24 KN.
Construction itself is a major challenge of the project. The machine required to build the greenhouse, lift the structure and covering material is too heavy for the roof. Therefore, the greenhouse builder cannot work with standard lifting machines and will assemble the greenhouse manually with scaffolding. This will increase the cost of the greenhouse.
The TERRA building is a recent building with modern energy management. This includes efficient insulation, ventilation, heating, and cooling systems. Moreover, the building has a technical hall dedicated to research on industrial food processing systems such as bakeries and refineries. All these devices produce heat, so that the hall needs to be actively cooled and ventilated all year long.
Due to the good insulation of the building, the greenhouse will not provide additive insulation to it. Therefore, the greenhouse will not recover heat from the building through the walls. The most obvious way to recover heat from the building would have been to use the air evacuated by the ventilation system, but the air outlet of the building is too far from the greenhouse. Carrying this air from the outlet to the greenhouse would not make sense from an energy point of view. The issue of proximity would have been easily corrected if it had been pointed out before the building was designed.
This project will increase the energy efficiency of the building and greenhouse by using the heat from the cooling system of the building to pre-heat the water going into the heating system of the building.
The shape of the greenhouse was also adapted to the building to increase its energy efficiency. The most popular greenhouse design is the chapel (see picture). This design is very efficient for large greenhouses. Nevertheless, in the case of a greenhouse standing against a wall fully exposed south, a half-chapel design increases energy capture by the greenhouse. In the case of the TERRA greenhouse, a half-chapel greenhouse will save 13% of heating energy compared to a chapel greenhouse.
The main compartment of the greenhouse will be 24 m long and 5.5 m wide. It will be dedicated to research on production systems adapted to rooftop farming in NWE. The greenhouse is designed to carry out experiments on the vegetables traditionally grown in the region and on plants producing medicinal molecules. This includes leafy greens (lettuce, chard, leek, etc.), herbs (basil, coriander, mint, etc.), fruit vegetables (tomato, pepper, eggplant, etc.) and medicinal plants such as hemp or euphorbia.
The objective of the greenhouse influences its design in two ways. Firstly, the greenhouse needs to produce a climate adapted to all these species all year long (cool in summer to grow leafy greens, hot and luminous in winter to grow fruit vegetables). Secondly, the climate (temperature, light) should be the same in all parts of the greenhouse to comply with the requirements of research.
The needs for modularity, accuracy, and an even climate control in this research greenhouse will result in devices that are generally not required in a production greenhouse. The greenhouse will be coated in double glazing for efficient insulation, equipped with energy screens, heating systems, cooling systems (fog) and artificial lighting.
The research carried out in the greenhouse will be associated with the use of bio-sourced fertilisers. The facilities will allow for the testing of different fertilisers simultaneously. Therefore, the RTG will be equipped with a set of 10 NFT tables. Each NFT table will consist of five gutters providing the same fertiliser solution.
The greenhouse will also include a 5.5 m wide and 6 m long demonstration compartment. This compartment will host innovative production systems such as hydroponics towers to give a feedback to the manufacturers, train university students and present these systems to the public.