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Jérôme Diot
Directeur technique développement durable et énergie
Published on March 21, 2019

Reading time : 2 min

La Nef: when a former mail sorting office becomes the first positive energy building in Tours

Near Tours railway station, the former postal sorting office is today a new-generation building used both for residential and tertiary purposes. The architectural project consisted of conserving the structure by dividing it into two blocks separated by a central “nave” which contains joint facilities. This is the inside story behind a major refurbishment.

- Crédits : © Egis

An efficient shell

External wall insulation was fitted onto the former concrete structure. It was made using prefabricated wooden panels containing the insulation material (22 cm of rock wool or glass wool) and the air-tight membrane.

The contractors were made aware of the importance of air-tightness very early on. Ultimately, performance is excellent in both the housing part (a Q4 at 0.6 m3/hm2) and the offices part (1 m3/hm2). Heat and acoustic insulation also obtain very good results.

Geothermal heating and free cooling

To combine complementary energy demands, we designed a geothermal heating system in which energy is transferred between the heating needs of the dwellings and the cooling needs of the offices.

The energy requirements are met by three heat pumps connected to a geothermal borehole and a storage reservoir for the frigories (unit of measurement of cold) generated by the pumps. This constitutes a stock of cold energy with which to control office temperatures using the free cooling technique, which is much more energy-efficient than traditional air conditioning.

Another specificity of the system is that the residual calories from the double flow mechanical ventilation, after the preheating of the input air, are transferred to the air/water heat pumps used as a backup for the geothermal installation. Finally, a green wall inside the Nave helps to cool the air naturally during the summer. It is irrigated with rainwater harvested from the roof (which is also used in the toilets).

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