Pilot building #1 :

    Building with six zero-energy thermal apartments for rent




    This building project of 6 apartments in Evere (Brussels) was initiated in 2014. The site is particularly well exposed but the reduced size of the plot (134 m2) and its angular shape have brought strong constraints. The choice of the zero thermal energy goal was realistic assuming an optimal use of geothermal resources. Few real estate projects are perfectly smooth. With this one, the first shovel added a year of delays and 7% additional costs. Indeed, the initial intent to built upon existing foundations collapsed together with a whole section of the periferals walls of the former cellars. We had then to completely rebuild the foundations using 10-meter deep secant piles plugged in the sandy-clay soil of this district of Brussels.


    Technical sheet

    The heated floor surface is 510 m² for 440 m² of private apartment. The thermal installation has been dimensioned to achieve a performance of 35 kWh/m².year or 18 MWh/year for the whole building. In order to maximize the renewable energy potential of the plot, we have installed four 130m vertical geothermal probes.


    The building was then constructed by pouring concrete into insulating concret form :

    • Construction technique : Insulating concrete forms
    • Insulation walls: outer 25 cm EPS and inner 5 cm
    • PVC windows frame: Triple glazing coefficient U = 0.7
    • Slate roof insulated by 15 cm of Polyurethane


    The thermal control of the building and domestic hot water are provided by two heat pumps of 10.3 kW each. The use of two heat pumps maximizes photovoltaic self-consumption. For example, if PAC 1 runs from 10AM to 2PM and PAC 2 from 12PM to 4PM, the power consumption profile is well aligned with that of photovoltaic production. Overall we expect a self-consumption rate of at least 60%.



    Results and learnings

    The building is not yet fully occupied so these are preliminary conclusions.


    After a period of freezes of several days and without any heating the average building température still exceeds 12°C.


    The installation of the freecooling system proved to be complex to implement. The initial plumber team had to be replaced by more experienced colleagues when we realized that the expected performance was not achieved. Indeed many errors of installation and configuration had to be corrected generating significant delays.


    Insulation schema



    Thermic schema



    Electric schema



    Performance monitoring

    The metering system collects every 15 minutes energy consumption data, temperature and humidity of each apartment as well as for thermal systems (heat pumps, hot loops and free cooling).