University of Minnesota’s Center for Sustainable Building Research’s John Carmody Discusses the Latest in Efficient Window Design

Written by AnonymousAugust 10, 2011
University of Minnesota’s Center for Sustainable Building Research

The University of Minnesota is one of the nation’s top public research universities and one of the most comprehensive public universities in the world. The University of Minnesota has five campus locations with 65,000 students and provides a thriving community for those with an overwhelming drive to teach and to learn, to research and to serve.

The University of Minnesota’s Center for Sustainable Building Research is dedicated to lead and support—through research, outreach, and education—the transformation of the built environment. The organization provides for the ecological, economic, and social needs of the present without compromising needs of the future. Further, the Center for Sustainable Building Research at the University of Minnesota is committed to conducting and sharing research needed to transform the built environment toward sustainability.

Last month, The University of Minnesota College of Design’s Center for Sustainable Building Research partnered with Minneapolis-based groups to design, build and compete in a Haiti home reconstruction project. The home was designed and built to be durable, sustainable, secure, and cost-effective.

We recently spoke with John Carmody, Professor and Director of the Center for Sustainable Building Research at the University of Minnesota to discuss some of the latest developments in efficient window design. Mr. Carmody has coauthored ten books, including, “Residential Windows:  A Guide to New Technologies and Energy Performance”, and “Window Systems for High Performance Buildings”. Mr. Carmody was one of the leaders of a team that developed the State of Minnesota Sustainable Building Guidelines required on State-funded buildings.

RWFD: What are some of the most significant developments in energy efficient window design—over the last decade—that benefit U.S. homeowners?

UofM:  The energy efficiency of windows has increased over the last 10 years through continuous improvements to the insulated glazing unit (IGU) as well as the window frame. The insulated glazing unit typically consists of two layers of glass separated by a spacer at the edge forming an air space. The edge is sealed and low-conductivity gas such as argon fills the space in between.  New materials and designs for spacers reduce thermal losses at the edge of the IGU. All types of Low-e coatings on the glass improve the insulating value. The coatings can be formulated to either permit passive solar gain or block solar heat gain depending on climate and house design. By adding a third pane of glass or plastic film between the glazing layers, even greater insulating values can be achieved. Common frames materials today such as wood, vinyl, fiberglass, and various composites all have good insulating values. Even greater efficiencies can be achieved by filling hollow frames with insulation.

The homeowner also benefits from the fact that the energy-related properties of windows are labeled by the National Fenestration Rating Council. Properties include the U-factor (insulating value), the solar heat gain coefficient (SHGC), visible transmittance (VT), and air leakage. If they meet certain criteria, windows can qualify for an Energy Star rating in different regions of the U.S.

The most important advice to any homeowner is to only buy windows with NFRC labels that meet the Energy Star criteria for your climate zone.

RWFD: What are three simple things a homeowner can do with the windows in their home to save energy and money?

UofM:  First, a homeowner must assess the condition and age of the windows in their home. If windows are older than 20 years and in poor condition, they are good candidates for complete replacement with new energy efficient units. If the homeowner is replacing the windows as part of a renovation project, the incremental cost of new, efficient windows is usually justified by the significant efficiency gains provided by installing new windows. New windows provide additional benefits such as improved comfort, reduced condensation and reduced maintenance.

However, if windows are still in relatively good condition but are uncomfortably cold and drafty in winter or permit solar gain and overheating of the house in summer, there are a number of things homeowners can do, short of full window replacement.

First, homeowners may consider installing awnings, roller shades or roller shutters on to the exterior of their home which can be highly effective in reducing solar heat gain in summer. Interior shades and blinds are also very good insulators which protect against solar heat, especially if they reflect solar gain back out through the window.

Second, from a cost savings standpoint, the easiest and least expensive thing homeowners can do is simply install conventional drapes, roller shades or louvered blinds on their windows. These simple measures can help homeowners save significantly on their monthly utility bills and will help keep a home more comfortable in the summer and winter months.

Finally, window sashes with more efficient glazing can also be replaced within an existing window. Storm windows (low- E storms are now available), and various methods of air sealing will also reduce winter heat loss


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