Net ZEB Case Studies - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 412

design. The closer collaboration also permits more communication between
architect and engineer, which becomes essential when designing the
intricate systems in high-performance buildings.
The following sections detail the elements that figured significantly in this
integrated design process.
7.4.2.2 Envelope
The exterior façade is constructed with modular precast concrete panels: 76
mm (3 in.) exterior concrete, RSI 2.5 (R 14) rigid foam insulation, and 152
mm (6 in.) interior concrete. The interior concrete surface is painted white
and left exposed. The roof is composed of a 76 mm (3 in.) concrete slab
poured on steel decking, with a layer of RSI 5.8 (R 33) insulation on the
exterior side of the concrete.
The window areas as a percentage of the façade areas are as follows: south,
30%; east, 32%; west, 31%; north, 21%. This is a very important design
parameter in Net ZEBs as it determines passive solar gains and useful
daylight throughout the year. The optimum window area as a percentage
of façade area depends on climate, function, selected shading/daylighting
device, control strategy, and importance of views to the exterior
(Tzempelikos, Athienitis, and Karava, 2007). The RSF has no separate
interior zone and has an open plan in order to maximize daylight
penetration and natural ventilation. The floor plate depth was chosen to be
18 m (60 ft) as a balance between exposed exterior wall area to volume ratio
and daylight availability.
The south-facing window aperture is divided into two portions. The lower
visionwindow istriple-glazed. Itslow-eglazing hasanRSI-valueof1.04,an
SHGC of 0.23, and a visible light transmittance of 43%. Insulated framing
decreases the assembly RSI-value to 0.52 (m 2 K/W) - half of the glazing
value. The upper daylighting window is double-glazed. Its low-e glazing
has an RSI-value of 0.65, SHGC of 0.38, and a visible light transmittance
of 70%. Insulated framing decreases the assembly RSI-value to 0.4. The
vision windowisusedforallofthenorth-facing windows. Specialized highly
reflective louvers are used on the top portion of the windows on the south
façade, as further explained later. These enable daylight to penetrate much
more deeply (at least double the depth) than would be possible without
the louvers. On the south façade, overhangs shade the lower vision glass.