Achieving real sustainability in building design and construction is more than just a checklist, though it often is distilled into one. Daylighting is one of those sustainable concepts that eludes easy categorization or measurement. It embodies the essence of integrated-design principles, requiring whole-building analysis and team consensus as early in the project as possible. It touches the foundations of the triple bottom line. It is Occam’s razor; an elegantly simple concept that pulls on every string of the web if it is to be successful. This is the beauty and the challenge of daylighting.
In terms of the triple bottom line, a comprehensive daylighting plan will impact each subset of the whole in the following ways:
• People: Daylight and views provide a strong connection to place and time. They promote healthy circadian rhythms; reduce stress; and possibly improve productivity, attentiveness and mood.
• Prosperity: Energy savings (kilowatts and kilowatt hours) come from reduced electrical lighting and cooling loads. Smaller cooling loads mean smaller HVAC systems that cost less.
• Planet: Reduced fossil-fuel use reduces global climate change by reducing emissions.
Many studies attempt to quantify the benefits of daylighting, but hard data is difficult to come by. The question “To daylight or not to daylight?” often becomes “Should we spend the money to daylight?”. The absence of scientific certainty and the risks involved make a decision to incorporate daylighting difficult, but the risks of no action are equivalent if not greater. A more valuable question might be, “What’s the risk of not doing it?”. Increased operational costs, premature obsolescence of a valuable asset (the building), disaffected employees, increased energy use—the list of consequences goes on. We must take anticipatory action to prevent potential negative consequences.
A DAYLIGHT PLAN
Because of the scope of the issues surrounding daylighting, it’s essential to have a comprehensive plan in place at the beginning of a project. This plan will cover metrics to track, project benchmarks and goals, and processes for coordinating the team throughout the entire design, construction and commissioning process. The team’s responsibilities with respect to the daylighting plan include the following:
• Architect—site analysis, orientation, massing, window-to-wall ratios and glazing selection
• Mechanical engineer—climate analysis, energy model and system sizing
• Electrical engineer, lighting designer and/or daylighting consultant—fixture and controls selection, daylight model and design integration
• Contractor—cost estimating, installation and coordination
• Interior designers—material selection (color, reflectance, etc.)
• Commissioning agent—commissioning and system monitoring
• Owner—facility management and operator training
As with any list, these responsibilities can be reassigned, shifted in the design phases and curtailed as long as they are adequately addressed in the plan. In fact, daylighting primarily is a matter of coordination; it involves the entire team early in the design process if it is to successfully meet each of the following six core principles:
• Usability—This principle tracks how much daylight is delivered and how much of the time you can rely on daylight to provide adequate light to the space. The most common expression of this would be the Daylight Factor, the complex basis of LEED for New Construction Indoor Environmental Quality credit 8.1. Additional considerations are user controls that allow adjustments to the amount of light admitted to the space.
• Thermal comfort—Typical commercial window assemblies have an average whole unit insulation value of about R-2, though superwindows can approach R-12. As such, consideration for balancing heat gain and loss throughout the envelope is a primary concern for the design concept.
• Glare control—An ideal daylighting plan will provide uniform light distribution that minimizes glare and hot spots.
• Energy savings (kWh)—Savings can be achieved by turning off or dimming electric lights when they are not needed.
• Peak load reduction (kW)—Peak loads typically are coincident with the optimal daylight conditions. Peak loads result in “ratchet charges” that can make up half of a customer’s utility bill. Additionally, the size of the cooling equipment is directly proportional to the peak load of a facility. Reducing the peak load has a significant impact on operational costs and first costs by utilizing smaller equipment.
• Views—This is perhaps the most subjective metric but arguably the most important. Excessively dark glass can shame an otherwise exemplary daylit design. Similarly, clear glass can admit too much glare, resulting in drawn shades and unintended use of artificial light. A balance must be established.
Some of these qualities are objective and measurable. Others are subjective. Do not make the mistake of overemphasizing the easily quantifiable metrics. Energy and daylight simulations are part of the whole, but they do not have the ability to describe the experiential qualities of the space. Daylighting has the potential to be a “form giver” for architecture, which is a unique opportunity compared to other sustainable strategies. Let the building tell the story of the light. You can have the most detailed studies and the most beautiful daylit renderings of a space, but the daylighting elements have an abnormally high risk of being value engineered out of a design. A comprehensive life-cycle analysis that addresses the entire system reduces the chance of that happening. Putting windows in a building does not constitute daylighting. Similarly, performance-based metrics will not result in projects that will inspire stewardship. Daylighting must join architecture and performance.
TATE WALKER is a senior project manager with the Madison, Wis.-based Energy Center of Wisconsin, which maintains the Daylighting Collaborative, a program that represents architects, engineers, daylighting designers and researchers, and product manufacturers to provide insight, feedback and recommendations to light every building using the sky. Walker can be reached at email@example.com or (608) 238-8276, ext. 118.
For new-construction projects, Washington, D.C.-based U.S. Green Building Council LEED credits under Indoor Environmental Quality 8.1 and 8.2 deal explicitly with daylighting but do not guarantee that all of the principles of daylighting will be met. LEED prerequisite 2 and credit 1 under Energy and Atmosphere address the central component of energy conservation as a result of daylighting. As codes have become increasingly stringent, advanced strategies for saving energy are necessary to meet the minimum two-point requirement for EAc1. EQc6.1 Lighting Controls addresses the challenge of coordinating the project’s automated controls for daylighting while allowing some autonomy for the building occupants. EQc6.2 Controllability of Systems and EQc7.1 Thermal Comfort reference ASHRAE standards 62.1, “Ventilation for Acceptable Indoor Air Quality,” and 55, “Thermal Environmental Conditions for Human Occupancy,” which are central to the amount of light and heat that comes as a consequence of daylighting. Natural ventilation has the potential to advance the daylighting strategy to the point where the building’s skin can replace the mechanical system for maintaining thermal comfort. Most importantly, integrated daylighting provides the opportunity for a project to propel the business model of an organization by requiring transparency in a project’s design, connecting natural light with the ancient metaphor for knowledge and putting people first.