A new view on energy efficient windows

By Juan Garcia

Keeping the warm air in, radiant heat out and built with non-conductive materials.

I have promoted ICF's and the Green Building Industry for many years. In truth I have felt that there were two problematic areas of all structures: the roof and the fenestrations (or windows and doors). Besides insulating the floor and adding radiant heat to this surface, the easiest and most cost efficient way to dramatically increase the efficiency of an ICF structure is focused on the window and door openings. A modern home may have 40 or more window and door openings. Each one of these openings is a serious threat to the integrity of the energy envelope.

Windows can make or break an energy efficient structure. They may exceed the number of doors often by ten fold and by their nature are light permeable. Like an invisible force this component of the structure is miraculously supposed to keep vapor (gas), moisture (liquids), thermal (heat) and finally audible (sound) from moving freely in and out of the structure. New technology is now available to increase the performance of the ICF. I say now available because the cost of using energy efficient windows is now in line with the return on investment.

There are multiple issues in choosing a window. I feel that the cardinal orientation or orientation to the sun (Solar Tuning) is the most important in both warm and cold climates. All structures should have different considerations for north, south, east and west faces. Within this framework I am reducing the considerations to the following issues: latitudes, predominant climates, direct sun or shade impacts and views for maximum energy efficient window planning for ICFs. There are six terms needed to define the window value to the energy package. These are defined as the following: U- Value (sum of convection, conduction and radiation), R- Value (previously defined as the movement of thermal (warm) air is now more generally defined as the resistance to heat transfer), SHGC (solar heat gain coefficient - is most important in warm climates and measures solar heat gain transmitted), VIS/Solar Tuning (visible light transmission) Heat Mirror Film (blocks the heat and allows light to pass through) and Gas Fill technology.

In reverse order, Gas Fill is simplified as the following. Argon is the standard glass fill and the least expensive. Krypton is more resistant to energy transfer and recently has become very expensive. The argon/krypton blends look to be the way of the future because the presence of krypton is what is germane with significant improvements in performance as the percentage of krypton gas increases.

Mirror (Heat Mirror) or Metalized Films in the modern application are utilized as one of the panes in the triple pane and quad pane (multi cavity) technology and provide the ultraviolet protection for the interior of the structure (people, floors, furniture, painted and stained surfaces etc.).

Visible light transmission/solar tuning is important because it defines the view. What good is a window if you have to have sunscreens, tints, louvered shutters on the outside and window treatments (blinds, drapes etc.) on the inside to try and achieve a comfortable condition (both physically and financially -energy bills)? Solar Tuning is an important consideration as a design feature for lighting specific rooms with available solar energy addressing diverse sets of problems and creating value in the room for entertaining, cooking, reading and daily work use.

SHGC is perhaps the least understood and most important in terms of the realization that energy from the sun should not simply be minimized in all cases. In lower latitudes, where heat gain from the sun is the most important issue because the dominant and most severe climate is warm to hot, then a SHGC is employed to minimize the heat gains in more faces of the structure. In higher latitudes, where the dominant and most severe climate is cool to very cold then the SHGC is factored differently in terms of faces.

R-Value is often an overused term, however in this case it is correctly applied to windows because of their direct application of stopping the flow of thermal energy (while the definition of R-Value has changed the tests have not). R-Values of 5 or higher are the goal of the US Department of Energy for all windows and higher values are recommended for severe climates.

U-Value is the total value for all energy moving in or out of a given structure or in this case element of the structure (windows). The sum of the convection, conduction and radiant energy that is credited to the windows is critical for the overall energy efficient calculations of the ICF structure. The value of the widow opening is often under utilized and sorely devalued for energy considerations. The most important opening in an ICF is the window area and the U-Value of that area which can number well above 30 per structure must be reevaluated for every green builder.

Notes on U-Value should be included with all windows that claim and energy rating. They are not. U-Value is a number which many builders base their choice of window glass. I have personally had consultants and builders say anything in the 20's (.29-.20) is what they look for in a glass package. What they fail to consider or calculate is the rest of the structure of the window. The true energy value of a fenestration is in its overall performance not a single consideration. What impact has an energy efficient widow glass package that is in an aluminum frame/sash? All metals are conductive, aluminum has a very high thermal coefficient - meaning that it takes on and gives off energy very quickly. Vinyl on the other hand is a very non-conductive material that is incredibly well suited for energy efficient fenestrations.

On October 23rd 2008 I attended the EEBA (Energy & Environment Building Association) 2008 Excellence in Building Conference and Expo in Phoenix, Arizona to sit in on a 1 hour educational session hosted by Ed Pollock and Marc LaFrance from the US Department of Energy called "High Performance Windows" from their Advance Track series of presentations. Among the key notes were the ideas that windows play a crucial roll in meeting energy efficiency standards in many national programs and that the DOE is working toward a zero net energy result with windows as a key component.
Among other discussions were the affordability of R-5 or higher windows with the ultimate goal being R-10, vinyl frame windows as the current preference for energy efficiency as well as VIS/Solar Tuning for the cardinal faces of the structure as appropriate for the environment.

Throughout the High Performance Windows discussions I kept silent (those of you who know me will understand the irony) and simply tried to absorb the information presented along with the frustrations voiced by the attendees, many of whom made very well crafted and valuable comments on window technology and the future of energy efficiency programming such as Energy Star and LEEDS. I was suitably impressed by the concern expressed by this group of more than 60 individuals and their drive to make the window issue featured as it should be in all new energy programs and legislation. Much of this discourse centered on Heat Mirror (metalized) film and gas fill technology.

Perhaps what I did not say, you may conclude, is what I am about to disclose to you, the reader of ICF Builder Magazine because this community is I believe the most important place to start in terms of new technology for energy efficiency. All of you know that I expound the benefits of ICF regardless of manufacturer as the most energy efficient structure available. Conversely I often shake my head at modern architecture of glass and steel structures (in which the R-Value is often below 2). So what is the new technology that I am so excited about? Primal Glass Systems made in the USA. It is, as many new concepts are, a construct of multiple known technologies assembled into a new product to produce an improved version of already functioning and tested components that when utilized together synergistically improve the characteristics of the individual components.

In an effort to clarify my statement this is my opinion. I have found a window that is so much better than anything else I have ever seen that I am now advising that this window is the only choice when it comes to economies of scale verses performance. This means that unless you have a customer with an unlimited budget you should use this window and nothing else for ICF construction. If your customer has unlimited funds then you have alternatives including ordering a "glass package" that is fitted into your choice of frame of this same Primal Glass technology.

In this new technology I have studied it is clear that the difference goes beyond simple energy efficient product and moves into a very important paradigm that I want to emphasize very strongly- money-money, money, money. What good does any new technology do anyone if it is inaccessible? This is so very important I want to repeat that any new technology regardless of its potential impact is useless technology if no one can access it or afford it once they have found out where to get it. How can I advise you to embrace anything that does not have a huge impact on your energy efficient structures that is financially out of reach for your customers? I cannot. The technology must be proven, tested and accessible to all. Return on investment should be consistent with individual expectations. Applications must be standard and easily understood.

The benefit of combining Mirror film and glass is unique in that metalized film provides the ultraviolet (UV) Light reduction that is not provided by the glass alone.
The true value of Primal Glass is the balance between heat and light, the allowance of visible light while still solving the problems of a given set of circumstances. I believe the future of energy efficiencies in windows is the best of glass technology combined with the best of film and gas fill technology. Low E 366 (low e 3) glass, Mirror Film and a gas fill which is itself a composite blend of two energy efficient elements argon and krypton.

Having products that can go from 64% visible light to 45% visible light, with changes in SHGC and U-value with R-values from 4.3 to 10 accordingly becomes invaluable for the window solutions. In fact this is a prime consideration in my holistic energy envelope theory for floors, walls and ceilings/roof issues. This product currently will meet and exceed the new US Department of Energy (DOE) Energy Star window performance standards proposed for 2013.

In conclusion windows are no longer an energy option. Windows are now and will continue to be the focus of all energy efficient buildings, accreditations and renewable programs. Regardless of what you know, don't know or think you know about energy efficient windows you can vastly improve the efficientcy of the structure by addressing the fenestrations for windows. Focusing on the holistic approach to the energy envelope will cause the components for the floors, walls and ceiling/roof areas to be treated with equal importance. In the case of the window openings there are many and each one is critical to the overall performance of the structure. Window fenestraitions need to be addressed for visable light transmission/solar tuning, U-value, R-value and SHGC for each of the cardinal orientations on the compass based on latitude and dominant climate considerations.

These products are now more affordable and accessible than ever before. For more information on the Primal Glass System please contact me at 602 460 7111.

Primal Consulting, Established 2005   |   Ph: (602) 460-7111   |  Email: JuanGarcia@primalconsulting.com |   © 2009 All Rights Reserved
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