Electrochromic Retrofit Window Coatings
Window Glazing: Thin-film electrochromic retrofit coatings vs. Conventional
Window coatings retrofitted to existing windows that can reduce solar heat gain and glare when the voltage to these thin films is adjusted (these have only recently become commercially available).
Item ID: 419
Building Envelope--Windows & Skylights
Technical Advisory Group: 2014 Commercial Building TAG (#9)
Average TAG Rating: 2.2 out of 5
TAG Ranking Date: 03/17/2014
TAG Rating Commentary:
- I support the concept strongly but see no indication that the company referenced in your info file has any viable technology that is close to market ready.
- I think the photograph shows thermo-chromic glazing. I am not familiar with this technology in the form of a retrofit coating. If it is the same coating that is used in electro-chromic glazing, I assume that they have the same performance. Electro-chromic glazings has been around for quite sometime. I am not sure how ready they are for the market in terms of cost and operational capabilities. New versions are expected that improve on operational capabilities and will hopefully be at lower cost. I do not know about the cost of the retrofit film.
- Film included
- My understanding is that these are not really market ready.
- Cost concerns.
Electrochromic (EC) solid-state retrofit window films have variable energy transmittance characteristics. By adjusting a small voltage applied to the coating, the window varies solar heat gain and visible light entering the space, increasing the window’s energy efficiency. Retrofit EC window films are not commercially available. US e-Chromic, founded in 2011, is conducting R&D aimed at commercializing retrofit EC technology developed by NREL. US e-Chromic's goal is to have a prototype delivered in February 2012 with commercial operation by 2013.
US e-Chromic's EC film can be applied to existing windows, transforming them into energy efficient 'smart' windows. US e-Chromic's EC thin film reflects sunlight and heat when activated. Reflecting heat enables this retrofit technology to be applied from inside an office or home onto existing windows, thus eliminating the costs, dislocation and landfill requirements associated with purchasing and installing replacement EC windows. Unlike conventional EC windows that are wired into the building infrastructure for power and control, US e-Chromic's film is powered with a small PV cell and battery. Wireless controls can interface with a building energy automation system.
Most EC technologies on the market absorb heat, and must be built into the interior of new window units, making them very expensive. Existing windows are replaced by new window units, potentially requiring vacating space and/or requiring rigging. Total installed cost is more than $60 to $80/ft2. US e-Chromic anticipates end-user pricing at approximately $20/ft2. EPRI states that EC coated windows could lower site-specific energy needs by as much as 40%.
Baseline Description: South- and west-facing commercial building space with conventional glazing
Baseline Energy Use: 10.5 kWh per year per square foot
The 2009 CommercialBuilding Stock Assessment gives the actual electrical building energy use index (EUI) for various types of heating and cooling systems (Table D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year, indicating that the combined HVAC heating and cooling energy use is 11.9 kWh/sf/year. (For all commercial buildings, the corresponding numbers are 19.9 and 9.4 kWh/sf/year, respectively for a heating and cooling use of 10.5 kWh/sf-year).
Since this technology can be applied to many types of commercial buildings, a baseline heating and cooling energy use of 10.5 kWh/sf-year is assumed (NEEA,12/21/2009).
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 19%
Annual boiler gas consumption was reduced by 19% after installation of electrochromic windows in a building in Colorado (mocked up in Window 6 and EnergyPlus). Annual HVAC energy use due to cooling equipment similarly was reduced by 22% in the modeling study. The baseline building used single-pane, clear, wood-framed windows.
Energy Use of Emerging Technology:
8.5 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 appropriate for virtually all commercial building except for warehouses and unconditioned spaces. However, this will be most appropriate, typically for just the south-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 50% of applicable space, which would count south-and west-facing perimeter zones plus half the interior space associated with those zones.
This number is further tempered as electrochromic windows can reduce only perimeter zone heating, ventilation, air conditioning, and lighting energy use. The savings is decreased due to buildings already deploying tinted and/or Low-E windows and due to buildings that use occupancy sensors and daylighting controls. The 2009 "Northwest Commercial Building Stock Assessment" indicates that 27.9% of commercial buildings have single layers of glazing. In addition, 53% of the windows are tinted. To reflect these constraints, the energy savings will be further reduced by 25% x 27.9% x 47% to yield an eligible square footage of 41,996,841 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% ||50% ||1,281,075,000 |
0.08 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): $15.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.01
Baseline Technology Unit Cost (Equipment Only): $0.01
Window area is assumed to consist of 25% of floor area. An initial cost of $60/sf--glass is thus equivalent to $15/sf--floor space. Cost-effectiveness will be significantly improved if future cost targets (i.e. $20/sf--glass) can be achieved.
Simple payback, new construction (years): 83.5
Simple payback, retrofit (years): 83.6
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.