Thermolite's Interior Curtain Wall Retrofit Found to Increase Energy Savings in Retro-Commissioned Building

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Thermolite’s RetroWAL™ interior curtain wall retrofit system disproves the myth that solar film is the only affordable solution for temperature control - it has been found to improve energy performance in an already retro-commissioned building.

Chicago office building

Chicago building retro-commissioned with solar film and supplemented with RetroWAL

Regarding temperature…there was a noticeable improvement on the average to above average summer days.

Thermolite’s RetroWAL™ interior curtain wall retrofit system has been found to increase annual energy savings by an average of 16% in a retro-commissioned building.

Thermolite installed supplemental windows onto the west-facing offices on the 20th floor of the office building in Chicago, Illinois, which had already undergone a retro-commissioning exercise that addressed heating, lighting, and building envelope improvements.

The following windows were monitored for three weeks to measure their energy performance:

  •     Window 1: 1/4 in. laminated glass with low-e hard coating (interior side)
  •     Window 2: 1 in. insulated glazing unit with low-e soft coating
  •     Window 3: 1/4 in. laminated glass with low-e hard coating (interior side) and 1 in. blinds in the air cavity

A 2014 case study of the building showed immediately apparent temperature control improvements after Thermolite’s three interior window retrofit systems retrofits were added, even though the Chicago building was already retrofitted for superior energy efficiency compared to its counterparts.

Temperature fluctuation was reduced to approximate set points of 68°F and 76°F (10°F difference) compared to the previous range of between 63°F and 92°F (29°F difference). The installation of supplemental windows in the building affects the heat transfer processes through the building’s envelope and their contribution to heat gains and losses in perimeter thermal zones.

“Regarding temperature…there was a noticeable improvement on the average to above average summer days,” according to an occupant of the office building.

Thermolite’s interior curtain wall retrofit window system was effective because it greatly reduces thermal conduction through glazing (due to higher R-value), direct solar radiation transmission through glazing into interior space (lower SHGC), and marginally reduces air infiltration.

Other key findings from the case study include:

  •     13-16% decrease in peak energy usage
  •     33-37% decrease in annual gas consumption
  •     5 Db reduction in sound level intensity

RetroWAL™ is the first Do It Yourself commercial curtain wall retrofit system that can easily be installed by a building’s maintenance staff within 10 minutes and without requiring structural reinforcement. Priced at less than $20 per square foot, RetroWAL™ shows it is better performing, yet just as quick and cost effective as solar film. View the 625 North Michigan Avenue Tower case study in its entirety.

About Thermolite

Thermolite has been providing energy and security window solutions to local and federal government agencies for over 30 years. Its advanced products and services reduce energy usage and improve security in the commercial building environment. Thermolite is the leader in blast mitigation, energy reduction, and hurricane interior window retrofit system technology. The factory is located in South Bend, Indiana.


Steve Champlin, President

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Steve Champlin, President
Thermolite Inc.

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