Lighting- control systems - Intelligent Buildings and Building Automation - page 222

spaces. Typical occupancy-monitoring techniques are the use of occupancy
sensors. Occupancy sensors usually employ motion detectors. A summary of
the types of occupancy sensors is given in Section 10.2.4.
Sensor-based control is also essentially used for both switching and dim-
ming controls to reduce the energy consumption of a lighting system by
maximizing the use of daylight. Open-loop control is typically implemented
by sensing the ambient daylight level. Closed-loop dimming control is also
commonly used by sensing the actual light (lux) level of the served indoor
spaces.
10.5.3 Use of daylight and blind/shade control
Making the best use of daylight is an obvious means of saving energy in
lighting systems. Glass is a key element in the architectural expression of the
building and typically provides indoor spaces with a visual connection with
the outdoors and daylight to enhance the quality of the indoor environment.
But the building skin must serve a crucial function in its role to help maintain
proper interior working environments under extremes of external environ-
mental conditions. Solar and daylight fluxes can vary very rapidly over a very
wide range. Controlling solar gain and managing daylight, view and glare are
issues for the effective use of daylight, and are still a challenge today.
Traditional manually operated mechanical shading systems such as blinds
or shades can be motorized and then controlled by occupant action or by
sensors and building controls. Emerging smart glass technology can even
dynamically change optical properties, and can be activated manually or by
automated control systems. In these cases, electric lighting should be control-
led as the backup to meet occupant needs, while maximizing energy efficiency
and minimizing electricity demand.
Manual operation of windows or shades may work well in homes and
some small buildings. But in a larger building with many occupants and
which aims to integrate the façade and lighting systems as well as HVAC
systems, more reliable automated controls are essential.
Motorized blind systems, such as venetian blind systems, are well-
established technologies for controlling solar gain and glare. Because both the
optical properties of the slats and their tilt can be controlled there is a wide
range of optical control available. Smart control on the automated blind sys-
tems can keep direct sun out of the space, reducing glare and cooling loads.
Motorized shade systems, such as roller shade systems, can provide a wide
range of solar optical properties. Although mechanically simpler, the shade
systems have more limited optical control than blinds in terms of position,
although it is also possible to layer blinds or use various fabrics.