Integrated Building Envelope, Daylighting, and Lighting
By Stephen Selkowitz
The interior floor space beside windows is the most “valued” space to employees who desire a view and connection with the outdoors. The intrinsic physiological and psychological underpinnings for these preferences are not fully understood although their consequences are clear. It is not an accident that “corner” offices with two windows are the prized upper-management spaces in a building. In European countries some unions require that all workers have a view of windows from their workstation.
Building perimeters are defined by the envelope that encloses them as well associated illumination. The envelope is often part of a much larger “design” statement linked to the overall building footprint, the “architectural statement” being made by the building owner. Smart owners ensure that design decisions around the external and internal building design and the relation to occupants have positive implications for energy use, load shape, and operating strategies within the building. Historically, the glazed building envelope was the weak thermal link in the building. This persists to a significant degree today, exacerbated by the architectural and owner preferences for highly glazed facades in many modern buildings. These designs admit more daylight and provide better connections with the outdoors from deeper in a space, but also become extreme challenges for energy efficiency and comfort if not designed and operated properly. Like the transparent envelope, lighting serves not only functional roles but helps define the aesthetics and ambience of building spaces for occupants. Since many business tasks are built upon "seeing" and visibility the role of lighting remains critical to occupant performance as well as comfort, even as the visual practices change i.e. from paper to VDT to laptop to tablet to phone) and the technology undergoes dramatic changes i.e. gas discharge lamps to solid state lighting with smart controls.
Applications
Proper envelope design begins with exploration of the footprint and orientation of the building. When placed on a green field site without constraints there are many opportunities to site the building and shape the floor plan to minimize purchased energy use and maximize comfort. The bigger challenges occur where site conditions constrain choices, as is common in urban environments. These site planning impacts of building footprint and envelope have an impact of the design of the overall campus, e.g. taller buildings in a denser planning mode provide less solar access and daylight but may reduce travel time and related energy use.
It is technically possible to make the envelope of the building a “net zero energy element” -- this is a stretch goal that supports efforts such as California's 2030 building performance targets. (CPUC 2011) While the fundamentals (minimize heat loss, manage solar gains, utilize daylight) are consistent across all building types and climates, the important details and design drivers change dramatically among climates based on temperature, cloud cover, and sunlight.
The building envelope includes both vertical and horizontal elements, where the ratio is driven by density, design and cost issues for a given site. A low-rise suburban campus will have a very different ratio than an urban campus. The relative importance of "roof" surfaces and "wall" surfaces is thus initially driven by these planning and design issues. Best practice today for opaque surfaces provides a highly insulating, low air/moisture permeability envelope and membrane. Surface optical properties are important: buildings with large flat roof surfaces, particularly in existing older buildings with sub-optimal insulation levels, will benefit from sunlight-reflecting "cool surfaces" (Heat Island Group website). Particularly in hot climates, these roof systems or overcoats should reflect the maximum solar energy, using a variety of spectrally selective surfaces that reject near infrared energy but allow colors.
In a highly glazed envelope (50 to 80% of total envelope) the challenges can be even more severe. Best practice for minimizing winter heat loss consist of multiple-glazed insulating glass units (IGUs) with low-E coatings and gas fill, placed within thermally broken metal frames. Triple-pane units are heavier, wider, and more costly, but are routinely used in Canada and Europe, and available in most of the U.S. as special-order items. (Carmody et al 2004)
Operable windows allow occupants (or automated systems) to open the sash to provide fresh air and potentially cooling for many operating hours of the year. The framing systems are more expensive than fixed glazing and reliable operation may be a challenge. Automation is an option although one that can add significant cost. In all curtain walls uncontrolled air leakage must be minimized.
Shading and daylighting are managed by “multiple” layers or defenses (Figure 1). A best-practice solution uses a spectrally selective glass with a high light transmittance and low solar heat gain coefficient (SHGC) to minimize cooling. Exterior shading is most effective and most costly; and most useful to minimize cooling in severe climates. Current practice includes fixed louvers and fins as well as operable, motorized units. Interior shading (blinds, roll-up shades) provide some sun control but also glare control for occupants. These can be manually operated or motorized and automated, at additional cost. While exterior shading and all motorized systems are rare in the U.S. they are widely used in Europe and are proven strategies where owners care about energy and resilience. As real and perceived cost and risk are reduced, industry leaders are (slowly) moving in the direction of delivering higher quality systems at lower cost.
Figure 1. Example of high performance façade used on the New York Times HQ tower in NYC. Consists of “layered” design solutions, A) inside-to-outside and B) floor-to-ceiling. A) consists of 1) External fixed ceramic rods for shading for solar control and daylight diffusion; 2) High performance insulating glass unit with spectrally selective low-E coating, argon gas fill and low-iron glass, including some fritted sections for glare control; 3) Interior automated, motorized roller shade with shade material selected to balance daylight admission and glare control. B) consists of 1) plenum and upper glazing zone for glare control and light diffusion; 2) central unobstructed vision area; 3) lower partially shaded zone that admits daylight to bounce off the unoccupied floor area adjacent to window. ( Lee et al, 2005)
The integration challenges of motorized systems with sensors linked to a BMS should not be underestimated. These solutions are bleeding edge today but should become more mainstream with time, as they have already in Europe. Smart glazings -- electrochromic and thermochromic – are now technically viable, but costly options, and require careful integration to optimize energy, daylight and comfort (Figure 2). Cooling cost tradeoffs apply to these as with other dynamic shading.
The final piece of the puzzle is daylight utilization -- both to enhance the workspace and offset electric lighting. The same shading and glazing must allow sufficient daylight to penetrate ideally 15 to 30 feet into the space, with photocells dimming the interior lights to continuously meet design illluminance levels (~300 lux for general office lighting). The window (or skylight) must be managed to minimize glare e.g., with shades or blinds. All too often manual shades are closed to control glare, and then never re-opened, with loss of daylight savings. On-off switching is not a satisfactory occupant solution, and the cost of daylight dimming is coming down as LED dimming is cheaper than dimming fluorescents and controls and sensors can be linked with cheaper wireless links and better user overrides. Daylight systems (dimmable fixtures and sensors) in practice today are often hit or miss in real offices due to design, installation and commissioning challenges. Competent design teams can make them work and they are deemed sufficiently robust that Title 24 requires it in all new California construction.
Figure 2. Emerging Smart Building Solutions. Schematic of “future proof” integrated solutions that link envelope and lighting solutions. Concept integrates four key features: 1) Operable façade components: Motors or actuators for shading devices, light-redirecting elements, operable windows, or switchable glass coatings; 2) Responsive lighting systems with dimmable output to match daylight, task needs and occupancy; 3) Occupant and sensor driven input for all systems control; 4) BMS controls integration that optimizes for comfort, owner cost, utility DR/price signals. (High Performance Building Facade Solutions, website)
Electric lighting has been a slowly changing landscape for many years with incremental improvements in the standard fluorescent lamp and fixtures. However, over the last decade the industry has been changed dramatically with the advent of white LED sources. While these add improved efficiency (moving well above 100 lumens/watt) the more transformative impacts are the provision of a wide range of lighting spatial distributions and intensities, the ability to provide more spatially granular solutions, the ability to dim lights smoothly and relatively cheaply, and the ability to sense and control these low voltage sources with wireless networks. Manufacturers are exploring future office environments with DC power distribution infrastructure to support low voltage lighting and a wide range of office computing and display equipment. (EMerge Alliance, 2015) As the efficiency of LED sources increases and net lighting power densities drop below 0.5W/sf, the traditional electric supply to lighting may be entirely displaced by a "power over ethernet" infrastructure. (Wikipedia, 2014) The overall control can be driven by local needs of occupants, automated occupancy and demand response, cost optimization from building automation systems, or any other facility manager need. As the controls industry matures, best practice should include automated commissioning, and other flexible control options to address functional changes in spaces, office churn, etc. Perhaps the biggest obstacle today is the lack of experience, skills, and infrastructure to rapidly absorb all the new technology and systems and ensure that they are properly specified and implemented. There are also a number of important technical subtleties that the industry is slowly addressing such as flicker, color temperature, color consistency, real lifetime and output, etc., and any proper LED based design needs to properly address all these factors for a successful solution.
Economics
The cost effectiveness of these individual and integrated solutions varies widely across a wide range of costs and benefits. Most of these systems can be "cost effective" when competitive markets offer them and first-cost savings for heating/cooling are accounted for, as well as changes in maintenance costs, e.g., due to longer-lasting LED light sources (Figure 3). Since the envelope is typically part of the overall architectural design, significant resources are often spent on design features independent of energy features. While building envelopes are relatively costly, they can have lifetimes of 50 years or more. There are a number of potential offsets noted in the text above in terms of chillers and cooling system rightsizing that bear consideration in the context of carefully and fully integrated system. While the sources/fixtures are more expensive than conventional sources, the systems solutions, including dimming, often are not and the new form factors of the lighting can make installation cheaper as well.
Figure 3. Perimeter-zone impacts on building systems. Design decisions made in the perimeter zone with respect to glazing, shading, lighting are often “Optimized” in a limited first cost/payback perspective (within the red box). A better solution is to optimize against “whole building investments” for building Chiller/HVAC sizing and on-site or off-site power investments ( blue and orange boundaries), allowing tradeoffs in first cost of chiller/HVAC system and power supply against an investment in high performance façade and lighting.
An additional potentially large benefit is that the high-performance, integrated, automated systems outlined above should deliver high levels of comfort and productivity immediately adjacent to the windows. Interior designers often push desks back 3 to 5 feet as a precaution against the expected discomfort immediately adjacent to the glass. The high performance systems described here can potentially recapture 2 to 4 sq ft of floor space per lineal foot of curtain wall [see Genentech case study]. At current construction costs this more than pays for the full cost of the high performance glazing, shading and lighting controls. Costs today for the controls infrastructure for these systems are highly variable, ranging from $2 to $8/sf (Wei e al 2012, Robinson et al, 2014), including not only the controls infrastructure with sensors but the need for dimming ballasts, fixture by fixture communications, installation and commissioning labor and integration with BMS or other building controls. However these costs are falling rapidly toward the low end of that range for new construction using LED fixtures with lower cost dimming and built in fixture by fixture sensors and wireless communications.
Finally the envelope and lighting designs have important impacts on occupants in terms of health, comfort and productivity, even when these are hard to measure. Since salaries are a factor of at least 100 greater than energy on a per square foot basis there are powerful economic drivers to invest in high performance solutions as a risk reduction strategy, even if the impacts cannot always be accurately quantified.
Institutional requirements & capacity
Mainstream conventional products can be obtained via multiple competitive channels but more innovative options are frequently more costly due to lack of competitive markets, complex supply chains, and added risk and uncertainty that comes with the use of new and unproven solutions. There are new procurement strategies that can in part address these challenges. The design - build - commission - operate paradigm is still a source of constant challenges as one moves across these life cycle stages.
Most decisions about the building envelope and lighting are driven by style, appearance, and other business image concerns as well as the more functional issues surrounding energy use. Internally the comfort and amenities offered to staff are crucial to a successful building design, and both the glazing/shading/daylighting features and the lighting solutions offer very strong positive reinforcement when done well but generate powerful negative effects when done poorly.
References
1. CPUC, California’s Energy Efficiency Strategic Plan 2011, http://www.energy.ca.gov/ab758/documents/CAEnergyEfficiencyStrategicPlan_Jan2011.pdf
2. Carmody, John, et al. 2004 Window Systems for High-Performance Buildings. New York, NY: W. W. Norton & Company, Inc.,, 2004.2.
2. Heat Island Group reference links: https://heatisland.lbl.gov/
3. Lee, E. S., et al. 2005. Daylighting the New York Times headquarters building: Final report. LBNL-57602 http://buildings.lbl.gov/sites/all/files/daylighting-nytimes-final.pdf
4. High Performance Building Facade Solutions, https://facades.lbl.gov/
5. EMerge Alliance, http://www.emergealliance.org/
6. Wikipedia, Power Over Ethernet, http://en.wikipedia.org/wiki/Power_over_Ethernet
7.Wei, J et al, 2012, Responsive Lighting Solutions, http://www.gsa.gov/portal/mediaId/197379/fileName/GPG_Occupant_Responsive_Lighting_09-2012.action
8. Robinson, A. et al, 2014, Integrated Daylighting Systems, http://www.gsa.gov/portal/content/193339