Sunshades and South-Facing Walls

by Jonathan McGaha | September 5, 2011 12:00 am

Sunshades deliver more than energy savings; they can become defining architectural elements

By Mark Robins

South Facing Walls One — Vertical Sunshades at Tarrant County College, Fort Worth, Texas

“Since 2007 the terminology associated with sunshades has changed, now they are being referred to more often as sun control devices, letting the owner know that there are benefits other than aesthetics associated with the product,” says Brian Clifford, director of business development architectural metals division, C.R. Laurence Co. Inc., Los Angeles. “On south-facing walls they will block sunlight in summer months, when the sun is higher in the sky reducing heat gain into the building, while allowing sunlight to enter the building in winter months, when the sun follows a lower path in the sky, thus allowing heat gain into the building.”

South Facing Walls Two — The 1600 Wall system with 1600 SunShade and custom vertical sunshades are installed on the Hot Springs Intermediate School, Hot Springs, Ark.

Over the past several years, metal sunshades have expanded to be a design and functional element for natural daylighting in modern medical, government, university and school building envelopes. “In addition to standard horizontal sunshades, new styles integrate into the design of the building, focusing on temperature management, solar energy collection and lighting functionality,” says Tom O’Malley, vice president of Doralco Architectural Metals, Alsip, Ill. “Sunshades can be used to mitigate temperature spikes during the day, to regulate spatial lighting for intense daylight scenarios or reflect indirect daylight further into rooms.”

Sunshades can shield not only windows, but also walls, air intakes and air conditioning units from solar gain. “Sunshades produce blockage of the sun rays that reduces the solar gain to the building, lowers cost of window glazing, reduces peak electrical demand, improves light quality through glare reduction, and increases the visibility in and out of the building without using dark tint window glazing,” says Curtis Yancey, national sales manager, United Enertech, Chattanooga, Tenn.

Sunshades can either be attached directly to the building structure or to the façade. “Single blade and outrigger-type sunshades are more prevalent, but there are other varieties available,” says Jot Chahal, product manager, Kawneer Co. Inc., Norcross, Ga. “Most sunshades are passive in nature-that is they do not change orientation based on environmental factors- but active sunshades hold promise for the future.” To provide additional shading, creative designers have even developed interior light shelves that direct natural light further into occupied spaces, enhancing the occupants’ connection with the outside environment.

Material Choices

Extruded aluminum is the material choice for louver sunshades. It is an extremely versatile material for engineering and constructing building products. It has a smooth surface and superior resistance to corrosion.

“Aluminum is 23.2 times stiffer than vinyl and 7.2 times stiffer than wood,” says Steve Fronek, P.E., LEED Green Associate and vice president of technical services, Wausau Window and Wall Systems, Wausau, Wis. “It is not susceptible to the instability and deterioration caused by shrinking and swelling. A workable rule-of-thumb for aluminum is its thermal expansion will equal 1/8-inch in 10 feet for a 100-degree temperature range. This exceptional material is extremely lightweight, and is quick and simple to extrude, machine and fabricate into virtually any form. These characteristics contribute to lower costs of finished aluminum parts, as well as lower shipping and handling expenses.

“Custom-extruded cross-sectional profiles give designers the ability to economically add an exciting bespoke element to their building envelope. It makes an excellent base for high-quality coatings that ensure a long-lasting, easy-to-maintain appearance. Aluminum accepts a wide range of surface finishes and protective coatings. It is recyclable and environmentally safe.”

Besides aluminum, many other materials have been used for sunshade devices, including stainless steel, galvanized steel, corrugated steel and pre-cast concrete. All can be used to block the sun and an architect may choose a particular building material based on its aesthetic appeal. “Your design is never limited and with all of these options you can put a unique and distinguished flair on your building … really make it stand out while also being efficient,” says O’Malley.

“The use of and installation of each material type will affect the overall project cost,” says Richard Braunstein, director of product development, YKK AP America Inc., Austell, Ga. “There is no singular ‘correct’ choice with respect to material specification. Depending on the method in which sunshades are attached to a building, the thermal efficiency of differing materials could influence the overall building’s thermal performance. For that reason it is important for the design team to review the impact of their material choice. This can be significant if the sunshades are directly attached to the fenestration system.”

Savings and South-Facing Walls

South-facing walls impact energy efficiency because heat gain from solar radiation is greatest from southern elevations. Because of this, architects must design sunshades specific to a building’s orientation, latitude, glazing size and purpose.

“A lot of this ‘solar control’ is an effort to reduce the peak electrical demands on a building and the electrical infrastructure in general,” says Eric Wiedman, LEED Green Associate and R&D manager of architectural louvers, grilles and sunshades, Construction Specialties Inc., Cranford, N.J. “Heat is gained and lost through all the elevations of a building during the course of the year. Three sides of the building will contribute more to the energy cost of running a building than the south side by itself. The problem is the peak cost of electricity during the summer cooling months. Utilities actually have a huge overcapacity of electrical generating stations, but most are kept in reserve for the spike in demand during the summer months. That wasted capacity is reflected in the cost of summer ‘peak’ pricing that all utilities charge between May and September. You see it on your residential bills just like commercial buildings do on a much greater scale. Controlling glare and the heat spike that comes with it is frankly harder to control on the east and west elevations than the south, but the south gets the attention since the heat gain can be so fast.”

With energy costs increasing for North America, many building owners are learning the value of sunshades. Lighting accounts for 40 percent of the energy used in a typical commercial building. A complete daylighting system including metal sunshades on south-facing walls can reduce HVAC peak loads with corresponding reductions in mechanical equipment capacity and carbon footprint.

“Costs of exterior sunshades are offset over the life of the building by savings in several areas [like] HVAC ‘first cost’ savings from reductions in peak load capacity and HVAC operating cost reductions from lower solar heat gain. Both are supplemented by reductions in heat generated by artificial lighting,” says Fronek. “Energy modeling tools, such as COMFEN by the Department of Energy’s Lawrence Berkeley National Laboratory, can help designers quantify savings and explore alternatives for perimeter zones of office buildings in several U.S. climate zones.”

An AMCA publication 530, a study by the University of Minnesota, shows south-facing walls energy savings have been calculated to be as high as 22 percent in Chicago, 25 percent in Houston, and 27 percent in Los Angeles and Washington, D.C. “These comparison values will vary depending on the size of windows, overhang distance and window glazing,” says Dane Carey, director of engineering at United Enertech. “These numbers are comparing two pane clear windows without any overhangs.”

To further boost energy efficiency, new technologies and improvements are being integrated into sunshades, including photovoltaic panels and automation to better track the sun. “This allows the sunshade to open and close as needed,” says Brett Reinhardt, marketing manager, Industrial Louvers Inc., Delano, Minn. “These technologies are more prevalent in European countries but are gaining some traction here in the U.S. There are thousands of configurations that can be used to provide energy-saving solutions. I believe that we have only begun to scratch the surface and as more information becomes available the use of sunshades will become a necessity rather than an option for building owners.”

Ask the Architects

Metal Architecture magazine asked three architects to describe in their own words their criteria for designing with sunshades and optimizing south-facing walls.

“We typically begin by computer modeling the building’s façades to simulate the sun’s seasonal angles for our latitude, and adjust the depth or shape of the shading device to allow some direct sunlight to penetrate during the cooler winter months but limit its penetration during the hotter summer months. This is then verified using energy software for calculating heat gain and loss through the particular glazing system with shading. Daylight modeling is then used to confirm sun penetration into the space to identify any issues with glare or over illumination.

Because glass is so desirable in current design trends, the need to control heat gain is paramount in maximizing energy efficiency. This is especially critical in commercial buildings where the greatest amount of energy is used cooling the building from its occupants. The introduction of sunshades and high-efficiency glass coatings has allowed architects the flexibility to bring daylight into the building to lessen the need for artificial light which also results in tremendous energy and cost savings. Proper daylighting is used in conjunction with lighting controls to maximize energy efficiency. Obviously, south-facing walls are the concern in the northern hemisphere whereas the north facing façade would be critical in the southern hemisphere.”

Matthew Wells, AIA, principal, ARCHITECTS hanna gabriel wells, San Diego

“Critical factors include orientation and transparency. Since the angle of the sun varies throughout the day, the position of the sunshade must account for that. The south façade is the easiest to shade (in the northern hemisphere) because the angle of the sun is so high relative to the building. Here louvers can run horizontal, creating a minimum interruption in views. The east and west facades, however, require shading that is nearly in front of the window, creating a challenge for allowing light and views while minimizing the incidence of sun on the window/wall surface. Here angled vertical fins are much more effective.

It is the overall design concept that most influences the selection. What is the building trying to relate to its occupants? What is the connection to its context and surroundings? These questions are critical in determining the method of shading. The fact is that shading is necessary-it’s a matter of how to accomplish it.

Proper building orientation is fundamental to energy efficiency. South-facing walls, especially here in Arizona, are preferred because the sun can be easily mitigated and taken advantage of throughout the year. Shading is easily accomplished by horizontal projections, while in the winter months, sun can be easily allowed to enter the building. By contrast, large exposures to the east and west are inherently more difficult to shade, so it fundamentally makes sense to minimize these facades.”

Jeff Kershaw, RA, debartolo architects, Phoenix

“The most critical considerations are the effectiveness of the design in terms of energy savings and aesthetic improvement of the interior environment (pleasant natural light) and the cost of the solar louver/sunshade device. There is a quantifiable savings in lighting and cooling lighting that can be modeled by computer programs evaluating these devices; this can be used to compare the first cost of the solar louver/sunshade with the value of energy savings over a given period of time. That payback period, or return on investment, is the critical point of consideration for most owners. Other incentives can be achievement of LEED goals undertaken by owners and their architects, and a desire to be environmentally responsible; to design a building that saves resources and still provides an excellent architectural interior (as opposed, for instance, to just making windows smaller or darker). The more pleasant, naturally illuminated space has been shown to be a more productive, healthier, happier environment for human activity, including work.

The term south-facing walls is commonly used today. Most likely because a south-facing wall will always “have sun” exposed to it. Why is this so important to you as an architect when designing a building in terms of energy efficiency? The southern exposure is highly valued by architects and planners because on earth, the sun appears to move symmetrically about a north-south axis as it rises, shines and sets each day. As such, it follows an arc in the heavens that is highest at noon, when the sun crosses the axis. The angle of the sun’s rays at noon is lower in the winter than in the summer, but for each day is steeper at noon than any other time of the day. So, the relative steepness of this angle of sunlight coming from the south, and the variation of that angle from steeper in the summer to less steep in the winter provide an opportunity to control the direct sunlight on the southern exposure. A relatively small overhang on the south façade above a window will allow that overhang to shade the window from direct sunlight during the hottest times of the day and year (hours around noon during the summer).

Conversely, in cooler climates the length of the overhang can be sized such that it allows the lower winter sun angles to penetrate the building through a window, thus contributing by passively heating the interior. The southern exposure is valued for the longer hours of sunlight that shine on that exposure. This is good for collecting energy from the sun (passive and active solar collection and daylight collection); it is also good for making an interior space pleasant. Daylight is the most efficient form of light for the eye, and daylight is necessary for psychological well being (depression accompanies daylight deprivation), and has sanitizing qualities in the environment. As humans we naturally like spaces that are day lit and they are better for us.”

Robert R. Balke, principal, director of the design for learning studio, tvsdesign, Atlanta

Source URL: https://www.metalarchitecture.com/articles/sunshades-and-south-facing-walls/