Heat-reflecting windows to slash Empire State emissions

The green makeover of one America's most iconic buildings, the Empire State Building, is to continue with a major new energy efficiency project that will see all of the skyscraper's 6,500 windows retrofitted with a new form of insulating glass.

The current double glazed windows will be taken out, and the existing insulating materials between their two panes will be replaced with a film that has been developed by insulation firm Southwall.

Dubbed the Heat Mirror, the insulating film works by increasing the number of cavities within a double-glazed window, to help trap the building's heat and block heat from the sun.

According to Southwall, the transparent insulating material increases the insulating value of the windows from R2 to R8, and will also reduce solar thermal gain during New York's hot summers by half.

The deployment of the material is part of a $13.2m (£8.55m) refurbishment programme that is designed to reduce the building's energy usage by 38 per cent a year, cutting energy bills by $4.4m in the process. Southwall expects the updated windows alone to save $400,000 in energy bills each year, or just under a tenth of the total energy savings from the overall retrofit project.

Other energy saving projects proposed as part of the plan include working with tenants to change floor layouts in order to increase the amount of natural light used in the building, and the installation of digital energy demand control systems.

The project team also decided to retrofit rather than replace the building's chiller plant, which was made possible thanks to the insulated windows' reduced load on the building's cooling system.

The Empire State building retrofit team includes the Clinton Climate Initiative, real estate firm Jones Lang LaSalle, the Rocky Mountain Institute, and Johnson Controls, which is handling the engineering, maintenance and construction work involved.