Is WTC glazing a sustainable building material option for a tomato greenhouse project in Brussels ?

Green spaces and flat roof surfaces in Brussels carry an important potential of development for urban agriculture and appear as a promising solution to take a step towards food self-sufficiency. On the other hand, Brussels also accumulates an important building material stock and rejects a large quantity of construction and demolition waste. A major reconfiguration of World Trade Center’s (WTC) towers 1 and 2 is currently under way in the Brussels North district, casting aside about 14 000m² of identical bronze-tinted double-glazed windows. Circular actors declared that no reuse option other than reusing them in urban greenhouses projects had been found. This Master’s thesis aims to verify whether reusing WTC glazing into a heated urban tomato greenhouse project is a more sustainable option than investing in a new horticultural glazing. Knowing that the most important part of the environmental impacts of a heated tomato greenhouse is its use phase, can reusing materials make a difference in the outcome? We used Life Cycle Assessment (LCA) methodology to compare the environmental impacts of three glazing options applied to a prototype. The three scenarios chosen are: reusing the double glazing “as it is” (WTC double scenario), reusing only the clear glass pane of WTC glazing (WTC simple scenario), and using brand new horticultural glazing (professional scenario). We chose the functional unit “the thermal and luminous atmosphere for producing one ton of tomatoes in an 18,7m² glass greenhouse heated at a temperature of minimum 18°C all year long in Brussels climate”. It turns out that the tomato production under a WTC double glazing greenhouse has higher environmental impacts than the two other options. Indeed, it is more insulating but also causes a poor yield and requires a heavier structure. On the other hand, reusing the clear side of WTC glazing has a lower environmental impact than the professional glazing scenario.
Some improvement levers of our prototype efficiency suggest that a non-tinted double glazing might be more appropriate for a greenhouse project than WTC glazing. This leads us to question the absence of data concerning the state of Brussels glazing stock, that ends up in landfills, or in the best case scenario to recycling. It could be reused instead, but a good knowledge of Brussel’s global situation is essential in order to make informed decisions that will make a difference in connecting different sectors and heading to a general transition towards circular and autonomous cities.