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Transforming a water tower into an “Urban Thermal Battery”

Transforming a drinking water reservoir into an urban “tank”, storing thermal solar energy and distributing it in winter for the area’s heating needs.

chateau d'eau solaireAt the heart of a neighbourhood currently undergoing renovation, the building, built in 1936, hasn’t been operated by the Syndicat des Eaux d’Ile-de-France for five years. It is in this context that in late 2008, the firm ELIOTH(1) responded to a call for ideas launched by the city for a sustainable use of the structure by proposing an original idea: transforming this drinking water reservoir into an urban “tank”, storing thermal solar energy and distributing it in winter for the neighbourhood’s heating needs.

This principle is strikingly simple, yet is the first of its kind: without the existing infrastructure, the idea of aboveground storage had always been hindered by the costs of building a tank and its supporting structure. But all it took was to install a hot-water circulation loop to supply the district’s main boiler, located just 100 metres from the water tower, and the entire system is automatically regulated according to need using temperature sensors. In terms of efficiency and performance, the study results are promising. The incorporation of 500 sqm of thermal sensors in the tank, along with the storage capacity of the water tower, means it can cover two thirds of the heating needs of the 65 future homes built in the area (low-energy housing) and supply almost half of the domestic hot water needs of more than 200 rehabilitated homes. With the quantity and compactness of the amount of water contained in the tank, a level of insulation equivalent to that of a new building is enough to maintain the water at a high temperature (70°C) until winter.

(1) Elioth, an Egis entity specialised in innovative structures, building envelopes and environmental design