Solar Control

 

Effective solar control in schools requires proper design and installation. Glass, framing, thermal barriers and shading devices are essential considerations of high-performance window systems that help control the solar spectrum.

 

A window system╒s components should be part of an integrated design for successful solar management and natural light. This design approach not only means working with the owner, occupants, facility manager and architect, it also includes working with the lighting engineer, mechanical

engineer, HVAC contractor, landscape architect and interior designer.

 

Early involvement of all building team members will contribute to energy savings, lower maintenance and extend durability. In addition, multiple studies show that student health and test scores are positively influenced by improved ventilation, indoor air quality and daylighting.

A complete daylighting system shades from direct sunlight, minimizes glare and heat gain and redirects visible light for illumination deeper within interior spaces.

 

Lighting accounts for 40 percent of the energy used in a typical commercial building. When properly executed, daylighting can reduce HVAC peak loads with corresponding reductions in mechanical equipment capacity and carbon footprint.

 

The most successful schools accomplish their green design goals using a whole-building approach, taking into account building envelope, site, orientation, HVAC and lighting systems.

 

The U.S. Green Building Council╒s LEED for Schools awards up to two points for daylighting in classrooms, with an additional point awarded for other occupied spaces.

 

Schools are ideal for harvesting daylight because they are primarily used during daytime hours and often are designed with open-plan layouts. Pragmatically, floor plan layouts should locate rooms with little use for natural daylight, such as washrooms and server rooms, in nonperimeter areas.
 

Activities within a daylit room should be oriented to minimize glare issues, such as facing computer monitors at right angles to incoming sunlight.

Schools also tend to have extensive high-ceiling space, facilitating top lighting with skylights and tubular daylighting devices. Clerestory windows can provide effective ceiling illumination while keeping the bright sun out of students╒ direct sightline. Unless downward view is important, vision glass below sill heights usually can be eliminated to reduce solar gain that carries no useful daylight.

 

 

The solar spectrum consists of ultraviolet light, visible light and infrared light. UV is invisible to the human eye, and long-term exposure damages materials, deteriorating plastic and fading furniture, fixtures and artwork. Visible light also can contribute to fading. Also invisible to the human eye, IR has a penetrating heat effect.

Typically, solar-reflective glass coatings dramatically reduce unwanted heat gain by reflecting and absorbing high amounts of IR and visible light. Spectrally selective glass coatings allow color flexibility in reflection and transmission while blocking a large portion of solar spectrum. Unlike static glass, electrochromic glass coatings electronically tint to provide dynamic solar control.

Schools can optimize glass selection through orientation, using clear substrates and coatings on north-facing faìades and darker glass on south-, east- and west-facing faìades. Similarly, darker glass should be considered for large windows and clearer glass for transom lites.

Exterior sun shades intercept unwanted solar heat gain before it can impact a building╒s HVAC system load, and they can also make a powerful aesthetic statement in a building╒s design.

 

Architects are exercising their creativity with sun shades using blades, tubes, catwalk grids, solid panels and louvers. Louvered sun shades can add diffusion to direct natural daylight for south, east and west facades. At the same time, exterior shelves are limited in their daylight redirecting effectiveness in the diffuse sunlight of overcast conditions.

 

Remember, exterior shelves or shades act as solar shading only for high sun angles. For high latitudes or east/west-facing facades, cut-off angles can be very low for occupied hours. Below this cut-off angle, supplemental interior shading must be employed to reduce glare from direct sunlight.

 

 

For interior applications, light shelves are most effective for relatively clear climates at mid-latitudes with south orientations. Typically, light shelves are attached to mullions and installed below clerestory or transom windows. This placement allows them to effectively redirect daylight onto a light-colored ceiling, improving penetration of natural light.

Standard white paint or clear anodized finishes are most appropriate for the top surface of light shelves. Generally, these finishes create matte or diffuse reflective surfaces to maintain cleanliness and functionality. Similarly, deep window sills finished in light colors are better than those finished in dark colors for reflecting direct sunlight upward.

 

It is estimated that output from a typical light fixture can be reduced by as much as 50 percent if it is not kept clean. The same applies to natural daylighting components such as light shelves. Cleaning is recommended every two years at a minimum and can be facilitated by removable or accessible components.

 

 

Between-glass blinds offer low maintenance needs and excellent thermal performance. Window blinds also act as effective solar shading, especially when coupled with exterior brise-soleil sun shades.

While reducing overall daylight transmission, between-glass blinds significantly improve daylight distribution through the space. Blind slats can be inverted to direct light upwards, if unconventional aesthetics and light leakage in the closed position are acceptable.

Steve Gille is education market manager at Wausau Window and Wall Systems. Contact him at education@wausauwindow.com.

Solar control and daylighting systems are best suited for schools under these conditions:

• The building team members are brought together early for an integrated design.

• The facility will be constructed on an unobstructed site in mid-latitudes with a clear climate.

• Whole-building energy modeling is planned.

• The design features expansive north- and south-facing faìades.

• An open-plan program will encompass much of the floor space.

• Atria, courtyards, light wells or high ceilings will be incorporated.

• Dimmable artificial lighting controls are available for critical spaces.

• Task area illumination will be provided.

• Blinds, drapes or shades can be used for glare control.

1. Redirect light to under-lit zones.

2. Provide daylight task illumination.

3. Improve visual comfort and control glare.

4. Optimize daylighting in conjunction with solar shading and thermal performance.