Engineered Window Louvers for Daylighting
Window Louvers: Engineered for Daylighting vs. Conventional
Integrated micro-louvers / blinds with curves engineered to redirect daylight coming through higher windows up toward the ceiling and further into a building without glare. Louvers are sandwiched within the window and either fixed or sun-tracking while lower windows have glare protection for occupant comfort (LightLouvers, LightShades, Okasolar/Okalux).
Item ID: 514
Building Envelope--Windows & Skylights
Technical Advisory Group: 2014 Commercial Building TAG (#9)
Average TAG Rating: 2.88 out of 5
TAG Ranking Date: 03/17/2014
TAG Rating Commentary:
- Lots of promise - increase daylight savings but also manage glare. Design integration is a challenge, as is cost; needs dimmable lighting to work
- My experience with light redirecting technologies, is that they work well when the sun is where they want it, but not as well when it is not. I think they deserve a serious evaluation in terms of energy savings and luminous performance in terms of occupant acceptance, as they can produce very bright patterns on the ceiling. The key is automated operation and I am not sure there are proven systems doing it today. However, there is potential for energy savings and daylight optimization if they are dynamic rather than static.
Baseline Description: South-, east-, and west-facing commercial building space with conventional glazing
Baseline Energy Use: 6 kWh per year per square foot
The electrical energy EUI for commercial buildings is about 17 kWh per square foot per year (From the 2009 Commercial Building Stock Assessment (CBSA) (NEEA, 2009 App D, Table D-EA1). This is the average electric energy usage index for all commercial buildings. The average lighting power density is about 1.15 Watts per square foot (page 28). With an average of 79.3 weekly hours of operation (Table C-SC2), annual lighting loads amount to 1.15 W/1000 x 79.3 x 52 = 5.97 kWh/sf-year (or about 35% of the commercial building sector's total load). HVAC interactions are neglected in this assessment.
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 16%
Energy Savings Reliability: 2 - Concept validated
Savings from this technology would be similar to those predicted for daylight redirecting films (DRFs, Technology #513). In a modeling study by Sacramento Municipal Utility District, the energy savings attributable to adding the DRF to windows adjacent to an area 24 feet deep with daylight harvesting controls on the lighting system already installed, tinted windows, and vertical blinds automatically controlled was approximately 16% (Note: this is not for all building square footage, but only for the area within 24 feet of the windows and only for interior space that is unobstructed). The lower range reflects an deeper study area and the upper range reflects a taller window with film on it. (Perry, 2012). Note that DRFs are equipped with diffusers to eliminate glare.
Energy Use of Emerging Technology:
5 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
This technology is most appropriate for new construction or retrofits in the commercial sector with unobstructed solar exposure for perimeter areas near south-, east-, and west-facing windows over six feet in height above the floor. A rough guess is that 10% to 20% of buildings might be suitable for use of the window louvres with only 10% to 20% of this population having glazing area at heights that are suitable for reflecting louvre application. Of the remaining building stock only those with relatively unobstructed floor plans within 24 feet of the windows and existing daylighting harvesting lighting controls should be considered. And for these buildings, only the 24-foot perimeter of those building areas can be included as building area that is affected by this technology (assume this represents 25% of the building stock).
This technology is appropriate for virtually all commercial building except for warehouses and unconditioned spaces. However, this will be most appropriate, typically for just the perimeter areas near south-, east-, and west-facing windows in the Northwest. The numbers for total commercial building space are taken from preliminary updated numbers from the 2013 update to the Commercial Building Stock Assessment (CBSA) using the estimates for 2014 (before the update was completed -- from early January, 2014), minus warehouse space, multiplied times the percentage of commercial space that is conditioned based on the 2009 CBSA, times our rough estimate of 25% of applicable space, which would count south-, east-, and west-facing perimeter zones. This result is then multiplied by 15% x 15% or 0.0225 to account for solar exposure and suitable window height yielding a total of 14,412,093 sf.
Regional Technical Potential:
| || Total Floor space || -s.f. Warehouse || non-Warehouse || % Conditioned || % Applicable || Applicable Space |
| Source || (NEEA, 2014) || (NEEA, 2009 App C) || (NEEA, 2009 App C) || (NEEA, 2009 App D, Table D-EA1) ||WSU EP || |
| Values: || 3,118,000,000 || 173,000,000 || 2,945,000,000 ||87.0% ||25% ||640,537,500 |
0.01 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Currently no data available.
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.