Page 171 - AGC_EN_iBook

171
a NEaRLy ZERO-ENERGy BUILDING
This chapter summarizes the main building physics requirements, focusing on energy ef ciency and related energy performance aspects.
tHe eNeRGy BaLaNCe OF a NeaRLy ZeRO-eNeRGy BuILDING
the concept of seasonal and daily storage
The challenge set by this project is to construct a nearly zero- energy of ce block in a low-density urban environment.Thanks to the use of high-performance heating, cooling and ventilation sys- tems, it is possible to signi cantly reduce energy use for heating and cooling. Power consumption for arti cial lighting is the one item in the energy balance most dif cult to reduce. Daylight avail- ability is therefore a key factor in the energy balance of a nearly zero-energy building. Moreover, daylight is not only important from an energy perspective, but is also a factor determining workplace viability and user-friendliness.
The following conditions play a key role in the project’s energy design:
–The low-density urban context provides a limited useful building oor surface (compared to the building’s footprint on the ground), enabling the use of solar energy on the roof (via solar panels or photovoltaic panels). Furthermore, the site lends itself to storing energy in the ground via geothermal boreholes.
– Neither district heating nor district cooling is available on the site.
–The suburban context enables optimal use of daylight.
These boundary conditions result in a solution combining the seasonal storage of energy in the ground and daily storage in a thermally active slab:
– a thermally active slab, loaded overnight with cold from the out- side air (free cooling), combined with convectors for supplementary local heating and cooling, and the supply of pre-treated fresh air;
– production of heat via a ground source heat pump covering 60% of the heating needs, as well as via an additional boiler;
– production of cold via a heat pump (dry cooler), by free cooling using outside air (dry cooler) and by free cooling using the ground (closed system with boreholes).
Daylight
The concept for daylight availability is based on three principles: 1) limiting the depth of the building; 2) ensuring that suf cient light is available on the facades; and 3) providing the facade with numerous user-control options.
The rst principle – limiting the building’s depth – has resulted in the building volume being indented, i.e., with separate of ce wings.The outdoor spaces between the wings are sized in line with the second principle, with the building’s geometry minimiz- ing shading from direct sunlight and minimizing blocking diffuse radiation on the internal facades.This has led to the wings being oriented at right angles to the north-south axis.
Details of the climate control systems
The following geometric parameters were taken into account for modelling the thermal activation of the slab: 4.0 m of embed- ded pipe per square metre of oor; distance between the pipes: 225 mm; 10% of surfaces left untreated, thickness of the concrete covering the pipes: 60 mm (bottom side); internal diameter of the pipes: 16 mm.The ow velocity of the water in the pipes is kept constant at 1 m/s (i.e., a ow rate of 0.2 kg/s).