Designing Residential Solar Control Solutions

Architects seeking to control sunlight and solar heat gains in residences, particularly those with large areas of glass or glazing, can use coiled wire fabric as an effective, economical, choice. There are fundamentally two common design strategies in this regard, one for interior applications and one for exteriors.

Photo courtesy of Matthew Millman Photography

Designer: Walker Warner Architects
“When we think of sun control and rainwater retention, we’re always searching for products that complement our palette of exterior materials. The copperclad Fabricoil is a natural choice for us. Whether we use it as a 20-foot-long rainwater diverter or a movable panel to cut the harsh sunlight, we’re always delighted by the results.” —Thomas Clapper, senior associate, LEED AP, architect, Walker Warner Architects

Interior Designs

In residential design, interior window treatments such as blinds, shades, or drapery, are probably the most common means of addressing solar control. They are inherently controllable with the ability to be readily adjusted for differing lighting conditions over the course of a day, week, month, or year. While the cost of traditional interior systems can vary, they are generally more economical than traditional exterior systems.

Instead of traditional window treatments, coiled wire fabric has been very successfully used as a durable, attractive, and economical alternative. In some cases, it may be the only treatment used or else it can be combined with other treatments such as black-out shades. Either way, there are multiple opportunities to create interior designs that blend the best of light filtering metal fabric with preferred colors, forms, and textures. Similarly, in cases where skylights or clerestories are part of the building, coiled wire fabric can be suspended below it in artful or simply functional ways to reduce glare, channel the daylight, or provide a curvilinear contrast to an otherwise rectilinear design.

Interior applications are where the fullness of the coiled wire fabric can play a big role. When more material is used than simply what is required to cover a given area, then a billowing, drapery effect may be achieved. This is consistent with other styles of interior window treatments and can create a rather luxurious look. The weave, color, and texture of the selected coiled wire fabric can belie the fact that it is not cloth fabric and therefore offer a warm and comfortable appearance.

Coiled wire fabric with fullness can be installed either as a fixed (i.e., always in one place) or an operable (i.e., able to open and close) drapery system depending on the type of attachment or track system being used. Curved, segmented, and straight systems are all possible so designing a fabric system to match a glazed opening or other feature can be very straightforward. This is true if small, single window units are the focus or if large, continuous glazed areas are part of the design. That is due to the ability of the coiled wire fabric to be provided in long, continuous sizes or to be seamlessly joined in the field such that no window opening size is too large or too small for consideration.

Another significant attribute of using coiled wire fabric for interior applications is its ability to allow for the predictable passage of air as well as light. Many exterior windows have HVAC components installed above, below, or adjacent to them that move air or radiant heat into the space. The coiled wire fabric typically is not bothered by the heat or cooling temperatures that emanate from these components and the open nature of the weave allows air and temperature to pass through the wire fabric. Hence, the light controlling aspects of the wire drapery will not necessarily interfere with the proper operation of the HVAC system the way that fabric drapery sometimes can.

Beyond the appearance and functional aspects of coiled wire fabric used on interiors, are the other performance capabilities that it provides. Fundamentally, it is a very durable choice since the metal coils are not hampered by many of the usage and wear concerns of other materials such as fabric, plastics, wood, etc. In fact, it may even protect the surfaces and glass that it covers. The overall appeal and durability often means that the material is not limited to covering windows on interiors but can be used elsewhere as a means to separate spaces, create a visual focus, or enhance lighting designs.

Photos courtesy of Cascade Architectural

The fullness of coiled wire fabric drapery is an important consideration in design. Fabric at 100 percent fullness is shown here on the left and 200 percent on the right.

Exterior Treatments

In some cases, residential building designs call for exterior components to be used for light and solar gain control. In that regard, coiled wire fabric has been used in several ways. First, the wire fabric can be installed in metal frames that are mounted directly to the building facade. The resulting scrim panels then cover over the glazing or openings and provide shading or penetration as desired. From the inside of the building, the view can be maintained much the same way ceramic frit on glass is used to allow a view but reflect sunlight. In some cases these exterior panels can be mounted on sliding hardware to allow them to move in front of the glazing or out of the way to let the sun shine directly into the building.

Instead of covering the windows or openings directly, panels can be installed so they extend horizontally above the fenestration. This creates shading by means of a projecting surface such that ambient light enters below the horizontal projection but direct light is from above is stopped or filtered. Energy codes recognize this approach as a Projection Factor (PF) that can be used to demonstrate code compliance for fenestration and daylighting.

Finally, there may be a preference for panels to stand up vertically in front of a building facade to provide solar shading particularly for east/west orientations, or to add another design element to a building. Coiled wire fabric can be used this way in framed vertically oriented panels to achieve these objectives. When the panels are attached to the building, they can appear as vertical louvers or accents. When separated from the building, it can help enclose an outdoor space or otherwise add to the three dimensionality of the building.

Energy Performance

With an understanding of how to use coiled wire fabric on the interior or exterior of residential buildings, the logical question is how well does it perform related to energy usage? To help answer that question, we can turn to an independent study carried out by the private firm of Interface Engineering. As one of the largest independent consulting engineering firms in the country, this 50-year-old firm maintains seven offices located throughout the United States with more than 275 employees. In 2014, it conducted a study of coiled wire fabric and its “Impact on Building Energy, Thermal Comfort, and Daylighting.” Using a combination of computational fluid dynamics (CFD) simulations and independent material testing, it was able to quantify different performance aspects of the material in different situations. Some of the findings reported in this study are summarized in the following paragraphs.

Source: Interface Engineering Report, 2014

Residential Energy Modeling Methodology

Multiple building energy simulations were conducted which compared energy consumption before and after the application of coiled wire fabric drapery. The energy modeling software eQUEST was used to conduct full year, hour-by-hour simulations to predict overall building energy consumption. A typical 2-story residence with a 25 percent window-to-wall ratio was chosen for simulation. Two different glazing types were simulated (standard single pane clear glazing and high-performance low-e glazing) with two shading strategies: drapery closed all year as well as an optimized strategy where the drapery is open when passive sunlight can be collected during the winter. To investigate how different climates affect the applicability of the material, simulations were conducted in several climates: Portland, Oregon; Phoenix; and Anchorage, Alaska. In total, 18 energy simulations were conducted and the results compiled.

Material Attributes

To create accurate simulations, independent laboratory testing was conducted of coiled wire fabric of different types over both clear and low-e glazing. In those controlled conditions, baseline solar heat gain coefficients (SHGC) and U-factors were determined and showed the following results just for the installed product conditions:

Building Energy Simulations

Based on the methodology and material attributes stated above, separate full building simulations were run to determine energy performance for each of the variable conditions and the different climate locations described. The resulting reduction in yearly energy consumption as a percentage of energy consumption when no shading device is used is shown as follows: Interface Engineering interpreted these residential building results by pointing out several things:

• Coiled wire fabric drapery is most effective when applied to the single pane glazing.
• An annual reduction of at least 3 percent is achievable in all climates simulated.
• The drapery is less effective when applied to the high-performance low-e glazing because the glazing has already significantly reduced heat transfer and solar gain capabilities.
• In the case of the low-e glazing, more energy savings is realized in colder climates.
• The “optimized” shading strategy proved effective for the single pane glazing in the cold climates. However, keeping the drapes closed is the most effective strategy for the low-e glazing in all climates.

The source of these reductions is found in the three common areas of heating energy, cooling energy, and fan energy. In cooler climates like Portland, Oregon, it found with the optimized control strategy, heating energy is reduced by 5.5 percent, cooling is reduced by 1.5 percent and fan energy is reduced by 10.6 percent.

Overall, the engineers determined that coiled wire fabric drapery can indeed serve to reduce a residential building’s annual energy consumption by up to 3.9 percent. The actual savings will, of course, depend heavily on local climate and the user’s operation of the shades. If the user is diligent in keeping the shades closed as often as possible, then the maximum benefit will be realized. It also noted that since the product has a more substantial impact on single clear glazing as opposed to low-e performance glazing, it can be a more appealing option in retrofit applications where existing glazing pre-dates current energy codes.

Shading and Glare Performance

Interface Engineering examined the use of coiled wire fabric drapery for shading and glare performance in residences as well. It found that “the best shading condition for this product is when the product is used in the 50 percent fullness configuration. Additional shading can be achieved when the material is changed either in wire gage or finish color.” It backs this up by pointing out that the material testing showed visible light transmittance (VLT) of 46 percent for the ³⁄₈-inch, 4-gauge 304 Stainless Steel at 0 percent fullness, which is 18 percent lower than the ¹⁄₄-inch, 19-gauge Silver Tin Plated. Of course, more fullness means more light and vision is blocked, with direct impacts on the lighting and views in the spaces.

Overall, Interface Engineering states, “The modeling results show that the best application for this product is glare control. The product is able to dramatically reduce the direct sun penetration into the room, even in the 0 percent fullness application. When the product is used in 50 percent fullness this glare control is greatly increased without a significant change to luminance levels further in the room.”

Conclusion

Residential projects can take many forms, but they all have a need to incorporate green and sustainable principles into their design. Healthy, outdoor spaces, especially in urban settings or restricted sites can be created successfully using adjustable pedestal deck systems over other surfaces such as roofs or tight ground spaces. Solar gain and glare can be controlled with coiled wire fabric products. Collectively, strategies like these can be used to create well-designed, functional, and sustainable residences.

Peter J. Arsenault, FAIA, NCARB, LEED AP, is a nationally known architect, consultant, con-tinuing education presenter, and prolific author advancing better building performance by design. www.pjaarch.com, www.linkedin.com/in/pjaarch