Technologies for Net Site Zero-Energy Buildings

Building energy simulation studies have more recently been commissioned by the US Department of Energy (DOE) to better understand the most effective ways to reach zero-energy building (ZEB) goals by 2025. These studies focused on estimating technical rather than market potential.

The National Renewable Energy Laboratory (NREL) completed an EnergyPlus simulation study in 2007 [1] to investigate the potential to reach ZEB goals across the entire US commercial buildings sector and with which technologies. The study estimated the maximum efficiency potential to reduce building energy use to net zero using a combination of efficiency measures.

NREL found that no single technology was found to produce dramatic improvements in efficiency needed to reach ZEB for a large fraction of the commercial building sector. Use of combinations of efficiency measures resulted in larger reductions than use of individual technologies alone.

In isolation, switchable high-R dynamic façades, which were controlled to minimize lighting and cooling energy use through its variable solar transmission, reduced sector-wide average energy use intensity by 7.5% if the base stock met 90.1-2004 Standard. Compare this to a 10% reduction if lighting efficiency was increased from 80 lumens per Watt (fluorescent) to 160 lumens per Watt (projected for solid state lighting efficiency), or a 7% reduction if opaque insulation levels were significantly increased to ASHRAE/ IESNA/ USGBC/ BSR Standard 189P levels. This study established the value of highly insulated and dynamic windows in combination with other efficiency measures in reaching ZEB goals.

[1] Griffith, B. et al. 2007. Assessment of the Technical Potential for Achieving Net Zero-Energy Buildings in the Commercial Sector. NREL/TP-550-41957.

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Dynamic Façades

The relationship between overhead lights, windows and HVAC.

Piecemeal to integrated solutions

Many design solutions rely on intelligent, dynamic façades to reach net zero energy goals. Dynamic or automated façade systems enable the reduction of lighting and HVAC end uses by leveraging the synergies of solar and daylight control on a real time basis. These systems can also deliver increased comfort, view, and amenity to occupants.

Relational chart illustrating how the Smart Control Algorithm (CPU) processes the information obtained from outdoor conditions, the dynamic façade, sensors, user input and utility demand signal and, in turn, affects the controllable lighting and HVAC EMCS.
Three columns of windows inside the LBNL Windows Testbed Facility; each column represents control over solar (left), daylight (center) and glare (right).

Switchable electrochromic windows provide variable solar, daylight, and glare control, shown at the LBNL Windows Testbed Facility.

An interior room of the New York Times Headquarters with automated shades, clear low-e glass, UFAD, low partitions, senors, digital lighting and exterior shading. Left: The same room at 9:00 AM: shades up, partial lighting; Right: a high dynamic range image at 9:00 AM Left: The same room at 1:00 PM: shades cover top one third, no lighting; Right: a high dynamic range image at 1:00 PM Left: The same room at 4:00 PM: shades completely, partial lighting; Right: a high dynamic range image at 4:00 PM Left: The same room at 5:00 PM: shades up, full lighting; Right: a high dynamic range image at 5:00 PM

(Left) The New York Times Headquarters in Manhattan combines a well daylit floorplate, perimeter open-plan offices, exterior shading, clear spectrally-selective low-e glass, automated interior shades, digital addressable lighting interface (DALI) lighting controls, and underfloor air distribution (UFAD) systems to achieve low-energy use with uncompromised views.

(Right) High dynamic range (HDR) digital images show luminance levels in a side-lit office with an automated roller shade over the course of a sunny day at the LBNL Windows Testbed Facility. HDR imaging enables more detailed evaluation of visual comfort.

Dynamic windows (switchable electrochromic windows, automated shades or blinds, operable windows) rely on sensors and control smarts to achieve high performance. Integrated façade solutions are networked with the HVAC and lighting control systems.

Field studies and computer simulations indicate significant technical potential for dynamic systems and broad applicability for commercial buildings with medium- to large-area windows.

For more information, see the Resources section.

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High-R Windows and Frames

Highly insulated or high-R windows are essential for reaching net zero energy goals for both commercial and residential buildings. In a project supported by DOE, LBNL is working to develop insulating glass units with center-of-glass U-factors of 0.1 Btu/hr-ft2-F (0.6 W/m2-C) or R-10 which will meet industry's cost, durability, and weight criteria. Current strategies used to reduce window heat loss are triple- or quadruple-pane glazing, which adds significant weight, or suspended films, which are costly. This project aims to develop lightweight, thin, non-structural central glazing layers, leading to highly insulating glazing systems that do not significantly increase manufacturing and installation costs.

Highly insulating window frames are also needed. As glazing systems improve, a greater percentage of window heat loss (up to 50%) is expected to be from frame areas, even with today's most efficient frames. Current research is aimed at understanding the potentials for using thermally broken "composite" materials, optimizing profile designs, and working with the plastics industry on new materials.

Key publications can be found at: Advanced Systems: High Performance Fenestration Systems

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Other Innovative Façade Technologies

There are many other innovative façade technologies and design strategies. This section will be expanded as more information becomes available.

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