Managing Daylight with Automated Solar Control  

In today’s world of rising energy costs, it is important to keep a handle on a building’s energy consumption. One of the easiest ways to do this is by using the sun’s natural light. The sun provides a building with free light and keeps it warm, and many studies have found that the sun’s natural light produces beneficial effects on building occupants. At the same time, however, sunlight can overrun a facility, causing problems such as high energy costs for constant air conditioning, eyestrain from glare on computers, hot spots in the building, and lethargy in employees. To keep out heat and glare while still maintaining a view for people inside the building, window shades are a first line of defense.

But there are shades, and there are shades. With the large amounts of glazing in today’s buildings, the solar shading industry has increased its offerings to effectively control daylight and reduce solar heat gain. Some of the most efficient solar control options are motorized window shades, which can automatically adjust to compensate for the changing shade requirements throughout the day, adding to occupant comfort as well as building energy performance. Automated shades react silently to the ever-changing nature of daylight, without the need for manual operation, to prevent glare and allow maximum usable daylight.

This article will provide an overview of the benefits of designing a space with ample views and daylight, the challenges this presents, and how motorized shading can help solve these issues. Under discussion will be the benefits of natural light, the importance of shade fabric selection, and the different motorization options, as well as the right time in the design process to discuss these issues.

Daylighting: The ABCs

The proper definition of daylighting—the harvesting of natural light—and its benefits are well known. Many studies, including groundbreaking research from the Hershong Mahone Group, have been conducted and the results are all very similar: natural light and connection to the outdoors via window views improve people’s mood and their general well being, they boost recovery rates in hospital patients and the test scores of students and, perhaps most important to building and company owners, they increase productivity and reduce the number of employee sick days. Operational performance increases, too, with often significant reductions in artificial light and HVAC usage. With commercial buildings representing just under one-fifth of U.S. energy consumption, and office space, retail space, and educational facilities constituting half of commercial sector energy consumption, reductions in building energy usage can add up to some pretty significant savings both in dollar amounts and greenhouse gas emissions. Owners and architects in virtually every building sector have joined the push to maximize natural daylight. A recent article titled “Best and Brightest” in United Airlines Hemisphere’s Magazine stated that some companies including major aerospace engineering firms maintain they have won billions of dollars in additional contracts by incorporating more natural light into their workspaces.

Shades play a crucial role in helping a facility reach daylighting autonomy, that is, the minimum use of artificial light, and the maximum use of natural light without being overcome by glare. When a person experiences glare coming in from a window directly in their face or on their computer screen, work performance can be adversely affected. Glare control, defined as improving visual comfort by blocking direct sun views while reducing brightness and contrast to manageable levels, in fact, can be a significant factor in daylighting strategies. If not controlled properly, glare can also affect interior lighting quality. The U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) Reference Guide notes in IEQ for Daylight, there are “acceptable and unacceptable forms of glare control devices. The major attribute all acceptable forms have is operability.” Absent a properly designed glare control strategy, a daylighting program is doomed to failure.

For reference in terms of designing for daylighting, architects should consult the Illuminating Engineering Society of North America (IESNA), which has been the reigning authority and has published Recommended Practice for Daylighting Buildings. This document serves to guide professionals through different design options and includes the latest data and technological solutions for meeting the challenges of daylighting while maximizing its benefits. Included is detailed information on design techniques, delivery methods, glazing systems, shading techniques, control strategies, and daylight performance simulation tools.

Daylighting With Shades

Shading systems are very useful as daylight management solutions that can mitigate both glare and heat gain while maximizing usable daylight in a building. Controllability of those shades is a key issue and can influence the achievable level of daylight autonomy. Shades can be either manual or automated and while they can both be fashioned from the same fabric, and similarly positioned, the manually operated shade will always be moved at the discretion of the building occupants. Industry studies have shown that, frequently, manual shades are only moved once or twice a day, if at all. Occupants have been known to be quick to lower a shade in the face of bright glare, but are not always as fast to raise it again when the glare situation has given way to more diffuse light. In some cases the shade is left drawn for extended periods, thus depriving the space of the human and operational benefits of subsequent daylight cycles.

The location and positioning of certain shades may put them out of easy reach, making manual adjustments difficult or even unfeasible. Another consideration is the sheer number of shades on a floor, against a certain façade or within an entire building—it is improbable that they will be properly deployed consistent with effective solar strategies. Lastly, manual shades can adversely affect building appearance as they are often left in a variety of different positions, creating a haphazard, less-than-uniform look on the building exterior.

Automated shades, on the other hand, do not share many of the drawbacks of their manual counterparts. Daylighting with automated shades benefits building occupants in a number of ways, principally by increasing personal comfort. The shades are preprogrammed to help diffuse bright sunlight by lowering to a predetermined position based on various factors involving the arc of the sun as it moves in the sky. In addition to blocking direct sunlight, the adjustments maximize usable daylight. Via sensors near windows, shade positions can be altered to keep them lowered on bright days, and raised on cloudier days to admit the more diffuse light into the building interior. Aesthetically, automated shades are aligned to specific preprogrammed levels, making a clean, crisp statement from both the interior and exterior of a building. In order to achieve LEED IEQ Daylight, glare control devices such as automated or manual shades must be provided.

Traditionally, one stumbling block to the decision to go with automated shades has been cost. However, as the benefits of daylighting and solar heat gain control become more valued, and even required, the cost obstacle recedes. When considering the total cost of a project and the premium automated solar control carries over manual solar control, it is also important to keep in mind the conclusions of industry studies—frequently manual shades are only being moved once or twice a day, therefore rendering an otherwise solid daylighting strategy ineffective.

Automation has been part of the built environment for quite some time. No one would think to manually turn on and off the heating or air conditioning because of solar heating gain or heat loss; thermostats are left to tell the heating or air conditioning system when to turn on and for how long. Keyless access systems keep track of who enters what door and at what time, and even faucets, toilets, paper towel dispensers, and hand dryers are automated, all with significant savings in costs. The trend to automation is well established, and it is only a matter of time until automated shades become standard practice in buildings of all types.

Energy Efficiency

It is no surprise that buildings with window shades are more energy efficient than those without shades. The accompanying chart compares energy conservation with and without shades for identical buildings located in each of the major U.S. cities listed for one full year. As can be seen, utilizing appropriate solar shading can save from approximately 15 percent to 75 percent on cooling costs depending on the location and climate, and on what fabric is chosen. This simulation was performed with several constants:

Fabric: 5 percent basket weave fabric is a charcoal color; 5 percent duplex fabric is charcoal/white color (with the white side facing the exterior).

Solar shading: The horizon is presumed to be at a vertical level of 5°. No other obstacles or buildings are taken into account.

Glazed surface in facade(s): 50 percent of the facade total surface. U-value of glazing: 2.9 W/m²K (i.e. 0.15˝ or 4 mm glass).

This information refers to interior shades only.

Shades made with PVC-free fabrics result in further energy savings, control natural light to the best advantage, and contain recycled materials. They are thinner and lighter than PVC fabrics, so they require smaller tubes and hardware systems, leading to less waste, lower operating weights, and smaller “bundle diameters."

Solar Variability

In order to more fully understand the benefits of automated shading systems, it is necessary to appreciate the basics of solar variability. The position of the sun varies from day to day, season to season, and by geographic location. The accompanying illustration shows the sun’s elevation from winter to summer months. The lower the sun’s elevation, the lower the solar protection needs to be to block glare and heat gain. It follows that, conversely, the higher the elevation of the sun, less solar protection is required, allowing for daylighting.

In the winter months, there is more of a glare issue, because the sun is not out long but it is low in the sky. In the summer months, there is more of a solar gain issue, because the sun is out a long time. The HVAC system must work longer to hold a consistent temperature if solar gain is not taken into account. The point to stress here is that daylight levels can vary widely both in terms of foot candles and quality of light, based on climatic conditions. For example, daylight that enters a building can be diffused by clouds, reflected off water or pour in from a bright sun with, of course, changes in angle and position as the earth makes it way around its orbit of the sun.

 

Automated shades account for all these factors and can automatically adjust the shades for occupant comfort. If constant shade movement is a concern, the scheduled automated shade movements can be programmed to adjust as frequently or infrequently as the owner or designer calls for. Shades can move in various percentage increments, i.e. 5 percent or 20 percent. Changing the percentage ultimately changes how many sun tracking movements will occur throughout each day.

Many commercial building spaces are including daylighting strategies, not only to be more efficient, but to also provide the proper amount of task lighting for optimal working conditions. Solar shades can work nicely in conjunction with artificial lighting control to optimize energy performance, or be a stand-alone system and create daylighting autonomy.

Options for Motorizing a Shade

Before considering the range of automated shading solutions, a brief look at how a shade is motorized is in order. The following are constituent parts of a motorized shade: the tube, motor, fabric, brackets, and fascia. The motor can be inserted into the tube and secured by either riveting the drive wheel to the tube or by the tube’s profile design. The fabric is affixed to the tube either by adhesive or spline attachment. In the first scenario, the adhesive would roll round and would not indent the fabric as a spline attachment can. The adhesive is merely for initially attaching the fabric to the tube and lining it up. The fabric wrap is what actually holds the fabric on the tube. The spline attachment scenario allows one to more easily change or replace fabric panels on installed shades. It is helpful to note that substantially larger and heavier products such as projection screens and wall dividers use adhesives, so each method has been tested and proven in service for years.

Generally speaking, brackets are mounted and the tube attaches to brackets. However, there are also other ways of mounting a shade, such as a head box/pocket scenario. Architects should also be aware of the cost advantages of coupled shades. Coupled shades are usually suggested by the window shade supplier after reviewing project specifications and submitting a bid package to the general contractor. This scenario can have several advantages, the most obvious of which is cost. Coupled shades reduce the number of motors required. Fewer motors mean less wiring, fewer circuits, conduits, and other accessories. In terms of tracking, coupled shades will always start and stop at the same time and ensure hem bar alignment.

Importance of Fabric Selection

It is important to note that while designers often select the fabric for a shading system based on its color, that color has important ramifications for solar control and daylight management. Failure to appreciate the potential of color in this respect can lead to not only wasting its potential benefits, but actually having adverse effects, such as creating glare at workstations and making interior spaces unnecessarily hot or cold.

The amount of solar energy and heat gain that enters a space through a window will be dependent on the type and color of the fabric chosen. Every fabric has three properties: solar absorption, solar reflection, and solar transmittance.

Solar absorption is the amount of solar radiation absorbed by the fabric. Solar reflection is the amount of solar radiation reflected back out of the space by the fabric. Solar transmittance is the amount of solar radiation that passes through the fabric into the interior of the space. These are the three ways that a shade can manage solar energy. When added together these always equal 100 percent.

Each type of fabric will have differences and hence advantages and disadvantages in managing solar energy. There are four properties of shade fabrics and openness factors. Dark color fabrics generally have the greatest solar absorption and least reflection, which normally enables them to provide better glare control. Darker color fabrics also provide a better view to the outside, and make it easier to view inside at night. Light colors, on the other hand, have a higher solar reflection, and a lower solar absorption compared to darker colored fabrics. They do not afford as clear a view to the outside as darker color fabrics, and they are harder to view through at night.

 

There is a type of hybrid fabric, however, called a duplex fabric that provides the best of both of both worlds: a high solar reflection factor along with good visibility. The inside of the fabric is a dark color, and the outside of the fabric facing the glass is either white, a light color, or metalized. The combination of these two features allows greater visibility and greater solar protection, along with glare control and heat control.

Another factor to consider in fabric selection is openness. Openness refers to the amount of the material’s open and/or closed space, that is, the density of its weave. A shade with low openness reflects more infrared rays, offers the best glare reduction and the greatest privacy during daytime hours. Designers looking for a fabric that affords a better view without reflecting as much infrared heat, while admitting more natural light into the building, should opt for a fabric with a high degree of openness; that is, a less dense fabric.

 

To put it succinctly, openness selection should be based on building position, geographical location or exposure area, office activity, elevation, and view, either clear or obstructed. In the accompanying map, there are recommendations for the window shade openness factor to control glare and work station reflections, for UV protection and for better view-through capabilities based on location.

 

Fenestration Data

Designers should look to manufacturers for the following information about their products, which proves to be quite useful in specifying shading systems that control light and heat, view and privacy, and glare level.
 

• Solar transmittance (TS), reflectance (RS), and absorptance (AS) add up to 100%, indicating that all the sun's energy striking the shade is reflected, absorbed, or passed through.
• Visible transmittance (TV) indicates the amount of glare likely to be perceived.
• Openness factor (OF) concerns the density of the weave.
• Shading coefficients (SC) indicate shading efficiency.

Further, manufacturers often have computerized tools to enable proper fabric selection based on the above-mentioned factors.

Motor Options

The type of motor is another variable that goes into shade system specification. Generally, motor types are distinguished by the power supply they require. There is line voltage, which is the standard wall outlet power, and there are low-voltage motors. Low-voltage motors require a transformer or a power supply to transform the 120VAC to 24VDC. Think of cell phone chargers or laptop computers, each one of which requires the use of power supplies. There are also battery powered motors for situations where it is impossible to pull wire to the motor location. These can also be powered by a solar array to charge the battery so battery replacement is kept to a minimum.

Motor control will vary depending on what type of motor was selected. The two basic classifications for motor types are standard and intelligent. Standard motors have no built-in intelligence and are 120V with a 4-wire pigtail; they require the use of an external motor controller to communicate whether the shade should be raised, lowered, etc. Intelligent motors have this control built directly into the motor.

The selection of a motor type will affect product hardware and its associated wiring as well as the tasks assigned to various types of engineers or contractors. An automated shade system consisting of standard motors, for example, requires the use of external motor controllers. The shade contractor is responsible for providing wiring diagrams showing motorized shade placement, low-voltage data, and line voltage, and the electrical contractor is responsible for mounting the controller, usually above the ceiling or in a control room if ceiling mounting is not an option. If controls need to be located in a dedicated electrical room, electrical wiring costs can increase dramatically, which means the overall cost of motorized shades increases as well. Standard motors do not keep track of their position, while intelligent motors do. There are motor controllers that can keep track of a current position very well based on a few factors, including timing and load sensing.

Intelligent motors are just that, intelligent. They employ circuitry inside the motor head which alleviates the need for an external motor controller. Circuitry inside the motor keeps track of the motor name and the motor I.D. as well as various group or zone assignments, and its exact position through the use of a digital encoder. On a standard 2-inch tube, there are hundreds or even thousands of stopping points to which the shade motor could be positioned.

Each individual motor can supply feedback to the control system indicating its current position. One of the biggest benefits of specifying intelligent motors is the electrical circuitry that is required. A typical 20A circuit can be run in series until maximum load conditions are met. It is simply a matter of supplying 120VAC to each motor or junction box location. Wiring for data is also simple. This can be done with cat5, cat5e, cat6, or whatever the low-voltage contractor has available, and is also run in series from motor to motor.

To recap, there are basic differences between standard and intelligent motors that architects should be aware of. While standard motors are easy to install and set up, an external controller is required and the motor position is not as precise. There is also limited feedback to the control system and the potential for higher electrical costs. With intelligent motor systems no external controller is required—the motor, not the controller, keeps track of the position, and the motor can supply feedback to the control system. Intelligent motor systems also have the advantage of being flexible, scalable, and programmable.

Now that the types of motors and the characteristics of each have been explored, a discussion of the possibilities of automated shades is in order. Designers and specifiers can choose from the following basic types of systems:

Manual Operation: This refers to motorized shades that are operated by the end user, either by wall switch or remote control, to the desired position.

Time Schedule Operation: In this modality, shades are sent to preprogrammed positions throughout the day, independent of external conditions. This mode can combine a mix of time, schedule, and manual operation.

Sun Sensor Operation: Once the strategically placed sun sensors measure sunlight intensity to be high enough, the shades are lowered to a position to protect the space from glare, solar radiation, and heat gain. This system incorporates the basics of automated sun control, which can also include manual control and time scheduling.

Sun Tracking: This is the most advanced stand-alone automated shade system. This system accounts for sunlight penetration variables, the position of the building, the time of day, and the time of year, and automatically adjusts the shades accordingly. The shading system can be manually overridden either via a wall switch or via a virtual switch on a computer.

Designers may also want to incorporate a useful product known as a bottom-up shade. Unlike traditional shades, these products provide privacy without eliminating natural daylight. Daylight is used to its fullest extent while protecting work surfaces near the windows from glare and excess heat. The shade rises from a roller at the bottom of the unit, blocking the sun’s rays at the bottom of the window, while allowing daylight to pass comfortably above people and objects adjacent to the window. It is important, however, that the draw cables that lift the shade fabric are under even and constant tension, allowing for easy operation. This lifts the shade fabric evenly and securely. In addition, bottom-up shades are most effective when used on the bottom couple of floors.

The effectiveness of bottom-up shades—and all automated shade solutions—can be improved through the use of interior light shelf units. A light shelf is a stationary shelf mounted midway down a window (for windows that are at or near eye level) or below the window (for windows located well above eye level). Light comes in through the top of the window and is reflected by the light shelf deeper into the building so the benefits of natural light are felt further away from the windows. Meanwhile, if located midway down the window, automated shades are used to control the glare below the light shelf.

Building System Integration

More and more, building system integration is being required. Integration allows a master or a central point of control, to direct multiple subsystems in the same project. Data communication protocols for building automation and control networks are widely used throughout commercial buildings in the U.S. and more than 30 other countries. This protocol allows various building devices to communicate with one another. Fire alarm systems, for example, can be equipped with relays to signal an alarm. These relays can be connected to an input on the shade system so that in the event the fire alarm goes off, all motorized shades automatically go to the up position and lock in that position until the firm alarm is turned off.

Motorized shades can be controlled through audiovisual systems of which there are numerous suppliers, or through any other third party or original equipment manufacturer (OEM) by using serial data transmission, mainly by RS-232 or RS-485. A comprehensive lighting control system is also an option. Natural light and artificial lighting controls can be integrated and controlled from the same system using a single wall switch.

The Design Process

Designing a well thought out and functioning automated window treatment system takes planning. Window shades are often seen by many as merely a fabric choice and the deciding factors are sometimes waited on too long. Electrical considerations, of which there are many, must be made by the architect and electrical engineer preferably early in the design process. Can the space accommodate line voltage wiring? Or, do the building structure and the design require the use of low-voltage motors? Will the shades fit with low-voltage motors or are the shade sizes too large to fit comfortably with this type of motor? Will there be any type of system integration? Will the automated shade system be integrated with an audiovisual system, a building information management system, or an overall lighting control system? Do the corresponding specification sections correlate to one another? Although snags in these situations can typically be rectified after the fact, they can end up being time consuming and ineffective from a cost perspective. In rare instances, a unique building situation may require a redesign or completely new design of certain types of hardware.

Architects and designers should take full advantage of the manufacturer’s product experts—they are a valuable yet often overlooked resource. Like many other automated systems, automated shade projects face a smoother operation when they are fully considered by all professionals involved in the task as early in the design process as possible.

Project Scenarios—Two Approaches

No two buildings will take the same approach to deployment of an automated shading system. Building orientation, geographic location, interior layout, budget, and other factors will best determine the appropriate configuration of the system. In the multi-floor office building in the accompanying photo, designers opted for a shading system specified to provide automatic glare and heat control. Included in the system is a sun sensor control with manual override. The offices are pictured with the shade alignment that occurs at 7PM.

In another case, a single-story office space was in need of a sun tracking system for its perimeter offices. The automated shading system was set to track the angle of the sun in 10 percent increments per the request of the owner. Manual override switches are provided in the conference rooms and the studios, with PC-based control of all shades enabled from individual offices.

Automated Shades: Letting the Sun Shine In…Correctly

As energy costs continue to rise, harnessing the power of the sun’s natural light is a valuable way of keeping a cap on building energy consumption. Increasingly, incorporating daylight is becoming a much sought after design goal in buildings of all types and sizes. Yet unmitigated daylight is not an option and can actually work against cost and comfort goals. A responsible daylight management system will regulate heat and glare to boost occupant comfort while decreasing costs of air conditioning and other energy expenditures. Shading systems represent a straightforward way to achieve these goals. Architects should be aware that automated systems in particular are a good means of solar control, and that considering such systems early in the design process can yield an important contribution to the building’s energy management and sustainability. 

 

Draper, Inc. is a Spiceland, Indiana-based manufacturer of window coverings, audio visual equipment, and gymnasium equipment. Draper has more than 110 years of experience in the window coverings industry. www.draperinc.com www.draperinc.com