Architectural Record BE - Building Enclosure

Managing Daylight with Automated Solar Control

Motorized shades lead to sustainable solutions
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Sponsored by Draper, Inc.

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.

Intelligent Line Voltage Application

Image courtesy of Draper, Inc.

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.

 

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