Comfort Considerations in Net ZEBs: Theory and Design - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 131

Howlett, 2003). Moreover, daylight and views may have a positive effect
on occupants' health, well-being, and productivity (Farley and Veitch, 2001;
Veitch and Galasiu, 2012). In addition, the presence of windows or skylights
on buildings may have a positive effect on retailing (Heschong, Wright, and
Okura, 2002). Finally, windows can provide useful passive solar gains and
offer a means, if operable, for occupants to introduce fresh outdoor air into
the space and increase local air speeds. All case studies in Chapter 7 , and
particularly ENERPOS and NREL RSF, demonstrate the driving role that
daylighting should play in buildings and their design process.
Despite the architectural, comfort, energy, and functional benefits of
glazing, it often adds to construction costs and may increase space
conditioning energy if not designed carefully. Glazing typically has lower
thermal resistance than opaque wall or roof constructions and can cause
unwanted solar gains - particularly in cooling-dominated climates and/or
buildings that have high internal gains.
Modestly sized windows with fixed shading devices are the preferred
configuration to simultaneously optimize energy performance and occupant
comfort. Façades with more than a 60% window-to-wall ratio should be
avoided, as they tend to cause thermal and visual discomfort due to excess
daylight and solar gains. Fixed shading devices function best for equator
facing façades and do not perform well for non-equator-facing façades; nor
do they offer privacy or the ability to darken a space (e.g., for presentations
or sleeping). Because of this lack of flexibility, dynamic shading systems
have gained popularity as a means to complement fixed shading. The
three-section façade concept (Tzempelikos and Athienitis, 2003) allows
fenestration systempropertiestobetailoredtotheparticularfunctionofthe
façade at different heights above the floor. A three-section façade ( Figure
3.5 ) consists of: (i) a bottom (spandrel) section, which is opaque (e.g.,
insulated wall) as it would contribute little to daylighting (LBNL, 1997), (ii)
amiddle(viewing)section,whichnormallyextendsfromtheworkplane(0.8
mabovethefloor)toabout1.5-2.0mabovethefloorandallowsviewstothe
outdoors, and (iii) a top (daylight) section, which has the primary function
of admitting daylight deep into the space while protecting occupants from
glare and direct solar radiation. When applied to shallow buildings,
three-section façades can be optimized to reduce electric lighting and
maximize natural ventilation (e.g., see the ENERPOS and NREL RSF case
studies in Chapter 7 ) . In addition, it has been shown that occupants prefer
shallow (no more than 15 or 20 m wall to wall) over deep buildings, due to