The design of a structure for human occupation is a complex task. It involves functional, structural, and mechanical relationships that require the coordination of many expert disciplines. Building material advances, systems advances, and the development of sophisticated computer modeling techniques can expand and enhance potential design solutions. Advanced design solutions require detailed analysis in order to identify material and performance optimization criteria. This identification process is difficult to complete.
The traditional methodology for the product design and delivery process of a building typically includes the architect, who independently completes the initial stages of design; a host of engineers and consultants who "cram and jam" component systems into the architect's design solution; and a return to the architect for coordination and assembly of final documentation and contract administration. This type of inefficient and uncoordinated design delivery process is slowly being replaced by an integrated team approach.
An integrated, or holistic design approach includes engineers, planners, and other consultants during the early planning and preliminary design phase. The early involvement of all required disciplines allows for a more integrated building design. It encourages early, open dialogue toward a "site-specific" design through an iterative process involving the various disciplines at the design phase.
Introducing feedback loops into the design process can impact building envelope and fenestration design. The holistic design approach more readily recognizes the vital interaction that takes place between individual building systems. Each building component is more likely to be viewed as a part of a larger whole and not as a separate entity, greatly improving building performance. For example, the optimization of a structure's fenestration design can have a ripple effect on many other building component systems.
The following scenario is a hypothetical building, designed by optimizing the fenestration system to achieve maximum, overall building energy efficiency.
Design solution: Daylighting optimization
Effect:
· reduced energy consumption due to reduced artificial lighting system run-time
· reduced electrical demand due to reduced lighting load during peak hours
· reduced cooling load on mechanical system due to reduced lighting loads
· a possible increased cooling load from daylighting fenestration system (a net cooling load reduction can be achieved through the use of spectrally selective windows)
Mechanical implications resulting from optimizing glazed surfaces:
· smaller chiller plant and reduced run-time
· smaller cooling tower
· smaller distribution system due to load reductions
· smaller heating plant and reduced run-time
· smaller mechanical room requirements
Cost implications:
· increased design costs
· reduced utility costs (energy and demand)-from lighting and heating, ventilation and air-conditioning (HVAC)
· reduced capital cost of HVAC equipment
· possible increase in the capital cost of lighting system
Modifying the process to accommodate early feedback loops can provide great benefits. Typical obstacles to using this approach include:
· holistic design is a more complicated approach and constitutes a significant break from traditional design;
· holistic design requires more analysis from the design team;
· frequently there is no financial incentive for the design team to provide this type of approach;
· the holistic design process requires specialized capabilities that may include the ability to use sophisticated computer software;
· holistic design requires the architect and owner to involve other disciplines early in the design process.
The term "fenestration" describes the physical arrangement of openings in a building's exterior envelope. This typically involves the design and disposition of window assemblies and doors. Component parts of a window assembly include frame, sash, glazing, spacers, and any accompanying hardware. Glazing describes the transparent or translucent component of the window assembly.
As noted previously, the fenestration design of a building can have a quantifiable impact on the energy performance characteristics of a building. It can also have an identifiable impact on the performance of a building's occupants. Design-behavior research has explored the effects on workers of various elements of workplace environments, such as lighting conditions, noise levels, views from windows, and office furniture arrangements. Such research has focused on the qualitative aspects of the work environment and on workers' perceptions of their surroundings. The quantification of potential gains in worker productivity, however, is difficult and context dependent.
Conversely, the potential energy use impacts of a structure are easily identified and quantified through simulation modeling techniques and can be confirmed through empirical validation. This report focuses on the quantifiable issues related to the fenestration design of a building.
Windows and Glazing
A brief examination into the historical development of windows reveals that the most basic function of a window opening is for the introduction of natural light and ventilation into the interior of a structure. The advent of clean and efficient mechanical systems has diminished one functional component, ventilation, by reducing natural ventilation requirements. Likewise, the improvement of artificial light sources has decreased the necessity for natural daylighting.
As environmental systems that control, modify, or simulate natural processes improve, the design parameters for windows and glazing systems are modified. In the 1970s, window design was focused toward mitigating unwanted solar heat gains and increasing window insulating abilities in response to the energy crisis. In the 1990's, the advancement of control technologies has encouraged a new building design paradigm of "smart" systems and neural networks that physically interact to provide comfortable interior spaces. For example, lighting systems can now be configured to automatically modulate depending on the amount of natural light within a space.
Improvements in fenestration system components (advanced glazings, improved glass coating and edge sealing techniques, suspended films, improved window frames, and sealant technologies) have substantially altered how windows function and impact interior spaces. However, these technological advances have not substantially altered the window's basic, historic function, and windows are once again being recognized for their daylighting abilities and their potential to provide energy savings and fresh air.