Written by John Edwards, Arjay’s Window Fashions
For those of you who have been following my articles on Fenestration in Window Covering News, you already know we have discussed some of the basics of how energy moves through glass and how to interpret the strange terms known as The Solar Optical Properties. Now, I would like you to join me in putting some of this knowledge to use. Our next step is to look at an imaginary window covering case study and apply what we have learned in Fenestration 101. We will first identify the problem – and then offer some solutions. Let’s go from information to application!
Our Problem Case Study
An office building located in Ventura, California (where we are located), with a very mild climate zone that produces August highs of 73.9 degrees Fahrenheit and December lows of 45.3 degrees Fahrenheit, along with an abundance of clear sky days, has a western elevation that is made up of butt-glazed clear glass double pane windows. The window mullion is anodized in a dark brown color and the existing window coverings are 1” aluminum mini blinds that match the dark bronze mullion in color. Your client, the building owner, sets the thermostat at 70 degrees Fahrenheit year round and is complaining of extreme heat in the afternoons on this side of the building; she even says that it gets too hot in the winter time on the west side of the building and she suspects that her windows or her window coverings might be the problem. She is asking us (you and me) to analyze the situation and come back with some recommendations. The building owner likes the bronze color of mini blinds because they match the bronze window mullion and if a change is required to solve the problem, she would prefer to stay with something in a dark bronze color. Now that we have all of the details, let’s get to work on identifying the problem and making some recommendations!
Our Fenestration Observations
- Even though the windows are only clear double glazed, and probably offer up a measly “R” value of about 2 (if we ignore the inefficient aluminum mullion), they should still be more than enough to deal with the very mild temperature differential of this climate zone. Commercial buildings are often times internally heat dominated due to the heat generated by lighting, computers, and of course, people. So, even when the ambient temperature drops, commercial buildings may not go into a heating cycle as often as residential buildings do — if they go into a heating cycle at all!
- We know that because the problem occurs in the afternoon, and that they experience afternoon heat in both summer and winter conditions, that this clearly points to solar gain as the culprit and not ambient temperature because the outside winter temperature drops below the desired inside temperature setting and the building is still getting hot.
- Finally, and most important, we all recognize that our client has giant solar collectors on the west side of her building that are masquerading as dark bronze mini blinds. We know from studying Fenestration 101 that the afternoon solar rays (short wave radiation) are passing through the unobstructed clear glass (we all know that it doesn’t matter that it is double pane) and are then being almost completely absorbed by the dark bronze color of the aluminum mini blinds and then converted to heat (long wave radiation) never to leave the building again.
The General Solution
The solution to our client’s problem is simple, and we have a number of different products available to us that will have a very positive impact on the comfort and energy efficiency of her building. We know from studying Fenestration 101 that what we need to do is trick the solar rays and send them back out through the glass in the same way they came in — as short wave radiation (light). We know that we need to find products with highly reflective surfaces (RS Solar Reflectance) or a low Solar Heat Gain Coefficient (SHGC) that will send the sunlight back out through the glass before it is converted to long wave radiation (heat) where it will be trapped inside the building.
Some Specific Product Suggestions
- Roller Shade utilizing Solar Screen materials with double weaves where the dark side of the material faces in and the outside fabric is light in color, so even though we see a dark color to the room side, the sun sees a light color and is tricked into leaving the building. Even more effective are the metalized screens that have highly reflective ambient surfaces and have excellent SHGC’s; these are my personal favorites when considering solar screens.
- Any horizontal louvered product with a white surface facing the window would be an obvious improvement over the dark bronze aluminum mini blinds. I prefer horizontal products to vertical because you can adjust the louvers to cross shade each other when there is a high profile sun and still maintain a view.
- Drapery with a white liner (white thermal liner would be even better) would have a tremendous impact on comfort and energy savings in addition to providing some added R value. Even though we determined that the major problem here is direct solar gain, there is nothing wrong with adding some additional R’s to the solution.
- Depending on our client’s budget, and what is going on around the windows, we could even offer to automate these window coverings (like the Roller Shades) and add simple timers or sun sensors that would employ the shades at the optimum performance time.
These are just a few suggestions for our imaginary case study and I am sure that you have some of your own. If you would like to focus on a case study in your area, real or imaginary, we could discuss different ways of looking at fenestration and window treatment solutions for a building in your part of the country. I would be happy to list you and your project in the upcoming issue and we could analyze it together in Window Covering News. That said, I am very interested in hearing from anyone with fenestration questions or suggestions; just contact me at Arjay’s Window Fashions!
Arjay’s Window Fashions is a certified consultation company on fenestration information and teaching you how to save money on your energy bills!. Please call us at 805.642.2300 for more information.
Serving all of Southern California including the greater Los Angeles County, Ventura County, Santa Barbara County and all surrounding areas.