Secondary Glazing Systems
Single-pane Window: With Secondary Glazing vs. Without Secondary Glazing
An insulated glazing unit (IGU) installed inside existing commercial building glazing that can triple its insulation value and reduce infiltration and outside noise at roughly half the cost of window replacement.
Item ID: 609
Building Envelope--Windows & Skylights
Technical Advisory Group: 2014 Commercial Building TAG (#9)
High performance secondary glazing units (also known as insulated glazing units, IGU) for commercial building single-pane retrofits that are installed on the interior side without replacing the existing glass, window frames, or altering the exterior appearance of the building. Annual total building energy savings can be up to 20% - primarily due to minimizing exterior solar heat gain loads and exterior air infiltration. Also increases occupant comfort thermally, visually, and acoustically in existing commercial buildings with single pane windows. Installation time is 2-3 times faster than a full window replacement--and much cheaper. The ideal application is existing buildings greater than 50,000 square feet with low-performance single pane windows in thermally unbroken metal frames constructed before 1990’s. (Curry, Pg 14-22).
Design considerations include fogging and seismic stability.
Baseline Energy Use: 19.9 kWh per year per square foot
Buildings with electric heating and cooling systems have an EUI of 19.9 kWh/sf-year (Table D-EA5).
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 20%
Energy Savings Reliability: 2 - Concept validated
Energy Use of Emerging Technology:
15.9 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:
The 2009 NEEA "Northwest Commercial Building Stock Assessment" indicates that 27.9% of the windows in commercial buildings have a single glazing layer (Table 12, Page 31). Schools have a higher percentage (46.7%) while office space is lower (22.5%). We also know that 27.1% of the regional floor area is heated by electricity (Table C-GB13). Buildings with electric heating and cooling systems have an EUI of 19.9 kWh/sf-year (Table D-EA5). Given a regional commercial building floor space of 2,704 million sf, the area that would be expected to have single-pane glazing with electric heating and cooling is about: 2,704,000,000 x (0.279) x ((0.271) = 204,446,736 sf.
This is from a presentation given by Rob Curry at the Northwest Energy Efficiency Alliance given April 16, 2014, for the E3T Commercial Technical Advisory Committee (TAG). (Curry, 2014 Pg 14)
Regional Technical Potential:
0.81 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)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $10.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.01
Baseline Technology Unit Cost (Equipment Only): $0.00
The total installed cost, as per a presentation by Rob Curry at NEEA (Curry, 2014 Pg 16), is $40 per square foot of glazing area. The comparison is against no investment. Building energy use and savings percentage are expressed in terms of building floor area, not window area. It will be assumed that the glazing area represents 25% of the floor area. When expressed is terms of cost per square foot of floor area, the technology unit cost is $10/sf.
Simple payback, new construction (years): 27.9
Simple payback, retrofit (years): 27.9
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.