“Energy-efficient windows will save homeowners money and offer peace of mind. Such windows reduce heating and cooling loads on the home, which in turn reduces the required size of the heating and cooling systems. Consequently, both fixed and operating costs decrease.”
– ECHO engineers, Team Ontario
In the first part of our interview with Team Ontario, we learned about their success at U.S. Solar Decathlon 2013. Here, in part two of that interview, we asked the team to share their perspective on energy-efficiency as it applies specifically to windows and doors.
JW: What elements contribute to making a window energy efficient?
TO: Within the industry you will commonly hear of three main criteria that affect a window’s energy efficiency:
Insulating capability – how well the window performs at keeping heat inside the home during the winter (heating) season and keeping heat outside the home during the summer (cooling) season. This is commonly referred to as the U value of the window assembly. The lower the U value the better the window is at reducing heat transfer through the assembly.
Solar heat gain – the amount of solar radiation that is allowed to pass through the window. A window with a high solar heat gain can reduce heating loads in the heating season but may also cause overheating within the home during the cooling season. Solar heat gain for a window is reported as the solar heat gain coefficient (SHGC) and must be selected to best meet the energy needs of the home without compromising occupant comfort.
Natural day lighting – the amount of visible light that is allowed to pass through a window. More light is generally better, but this comes with a compromise of insulating capability and solar heat gain criteria. The amount of visible light a window allows to pass through it is referred to as visible transmittance (VT).
For a homeowner or designer, there is a balancing act of these three criteria that is required to select a truly energy-efficient window for the required structure. When done properly, windows can significantly reduce heating and cooling loads while still allowing an appropriate amount of natural light into the home.
JW: What are the benefits of using energy-efficient windows in a residential home?
TO: Energy-efficient windows will save homeowners money and offer peace of mind. Such windows reduce heating and cooling loads on the home, which in turn reduces the required size of the heating and cooling systems. Consequently, both fixed and operating costs decrease. Additionally, professionally installed, energy-efficient windows can greatly improve comfort within a home. Drafts and cold spots that are typically found around windows in a room, excessive solar heat gains, and unpleasant glare can all be significantly reduced.
JW: What are the challenges of using energy-efficient windows in a residential home?
TO: The greatest challenge in using EE windows in a residential home is the cost of retrofitting them onto existing structures and ensuring the appropriate windows are selected for the application. Developers also need to be convinced of the long-term value of installing them on new homes, as opposed to opting for cheaper windows that bring down the face value of homes for prospective buyers.
JW: What elements contribute to an energy-efficient door?
TO: With doors, compared to windows, there is less concern about the solar heat-gain coefficient and visible transmittance of a door. This is because unless a door has glass panels, both the solar heat-gain coefficient and visible transmittance will be zero. Therefore, the major concern is insulating capability in the form of a low U value. To produce an energy-efficient door, it is also important to reduce or eliminate air leakage through the seals around the door frame. If a door does have glass panels, the same benefits and challenges as mentioned for choosing energy-efficient windows will apply, and an even greater emphasis may be placed on aesthetics.
JW: From a home building, engineering and efficiency perspective, what qualities do you look for in a good window or door?
TO: From an engineering standpoint when building an energy-efficient house, it is particularly important to pay attention to the overall size, location and orientation of your windows and doors for the greatest impact. All of the previously mentioned elements—U value, SHGC, VT and air leakage—of EE windows and doors are important and, if possible, from an engineer’s perspective it would be nice to select these criteria based on an energy model of the entire home. This is now becoming more common in the custom home sector of the residential market.
JELD-WEN congratulates Team Ontario on its success at the U.S. Department of Energy Solar Decathlon 2013 last month, and on forging a path that promotes sustainable living by creating an eco-friendly structure that is viable, affordable and inspiring.