BUILDINGS - Smarter Facilities Management

07/25/2016

Squeeze Efficiency from Window Upgrades

The investment is substantial, but the benefits of energy-efficient windows outweigh the costs

By Robert Nieminen

 

According to one ENERGY STAR estimate, a 10% decrease in energy use for a 200,000-square foot building that spends $2 per square foot in energy would boost the property’s net operating income by $40,000 annually.

Window replacement isn’t cheap, but neither are existing windows that are out of date and inefficient. The opportunity to upgrade comes around infrequently – possibly as part of a broader energy conservation plan funded by one financial package – so owners must maximize their return.

“Windows are an important contributor to the building envelope and can be an integral part of energy conservation strategies,” explains Kerry Haglund, Research Fellow for the Center for Sustainable Building Research at the University of Minnesota, in his report “Window Selection Methodologies and Optimization in High-Performance Commercial Buildings.” In fact, the report estimates that 39% of commercial heating energy use and 28% of commercial cooling energy use – 34% of all commercial space conditioning energy use – are attributable to windows (excluding infiltration).

Fortunately, improvements in window technology have greatly improved the performance of window and glazing systems. Today’s windows have lower heat loss, less air leakage and warmer surfaces that help to improve occupant comfort while minimizing condensation. With features such as double- or triple-glazed insulated glass, improved frames and specialized coatings and films, these high-performance windows are effective at reducing heat transfer.

To make a positive investment in a window upgrade, building owners and facility managers should be familiar with specifications, performance measurements, costs and energy savings.

A Holistic Hole in the Existing Wall

Window and glazing options have a number of impacts that should be considered holistically with existing conditions, such as building use, local climate, utility rates, and building orientation. According to the National Institute of Building Science’s Whole Building Design Guide, these impacts include:

■    Heat gains and losses
■    Visual requirements (privacy, glare, view)
■    Shading and sun control    
■    Thermal comfort
■    Condensation control
■    Ultraviolet control
■    Acoustic control
■    Color effects
■    Daylighting
■    Energy requirements


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