Whether a building runs on conventional or exotic energy sources, optimizing its energy consumption and satisfying users with the way it operates has never been easier, thanks to a new generation of advanced control technologies for air conditioning and lighting.
From online software that can control multiple buildings to wireless controls for individual rooms, these new technologies promise to pay for themselves in efficiency and flexibility as well as energy savings.
Trane, the air-conditioning systems and services business of American Standard Companies, recently introduced its Tracer ES (Tracer Enterprise Solutions), a new Web- and server-based facility-management system, along with Wireless Zone Sensor, a new version of the familiar wall-mounted thermostat.
Access From Anywhere
As part of a $13 million upgrade of its energy-management technology, South Carolina’s largest public school district installed a Tracer ES computer software system in February 2006. Encompassing most of Greenville County and parts of two adjoining counties, Laurens and Spartanburg, the Greenville County School District extends across 800 square miles. With 95 schools, 65,287 students, and a staff of 8,004, it ranks 58th in size nationwide.
“Tracer ES allows access to all of the district’s schools from anywhere in the district,” says Devie Erickson, senior product manager for Trane Global Controls Systems in St. Paul, MN. “The maintenance staff can get information on the status of equipment or systems in any building.
“For a chiller plant, for example, the system will tell them its flow rate and its supply-and-return temperatures, and help them determine whether it is operating efficiently and effectively. If an alarm comes in, they can go online to access information on the piece of equipment that generated the alarm and understand what is causing the problem.”
Via Internet browsers, any computer on the district’s network can enter the Tracer ES system. Employees and servicing companies outside the network can gain access through a secure VPN (virtual private network).
In addition to maintenance staff members, system users include district facility managers who ensure the comfort and safety of the students and staff, and administrators who want information on metrics (such as energy use per square foot and indoor air quality) to share with the school board and the community.
“The system manages the energy use of HVAC (heating, ventilation, and air conditioning) equipment and lighting in the school district’s buildings,” Erickson says. “It could also tie into water meters, but in this case it does not.”
Theoretically, the system could operate on alternative energy sources if grid power were to fail, but it’s not connected to the standby generators that run emergency systems in each school.
The system also could be programmed so a failure of grid power and activation of standby generators would trigger a separate input signal at the enterprise level, telling the Tracer ES to keep critical equipment and systems running on generator power and shut down everything else.
Software On Disk
The Tracer ES came to Greenville on a CD-ROM. Trane engineers installed it in the school district’s computer network. “Each school had an existing controller. The enterprise layer recognizes all the schools and each piece of equipment in every school, and brings that information to a central server in the main administration building in Greenville,” Erickson says.
Tracer ES was specifically customized for Greenville to emulate the entire system within that server. Auto-recognition capabilities minimized the programming time. “We put in the network address for the controller in a school, allowing the Tracer ES to locate that instrument panel, recognize those pieces of equipment, transmit the information back to the server, and configure Web pages to provide the status of that equipment automatically,” Erickson says.
The system has been customized further for each individual user within the Greenville district. “It has tools with a search-engine functionality, allowing a user to see a list of all elementary schools or to request a list according to his or her specific needs,” Erickson says. “You can view all the buildings in the school district, decide what school you want to look at, then view it graphically and textually in a Web-page format, on a map, or in a navigation tree.”
The district has five regions, each with its own facilities manager and maintenance staff. The system allows people working in each region to choose only the schools within their own region.
Tracer ES allows facility managers to establish schedules for maintaining a desirable temperature level in the classroom during operating hours. “The systems below it are smart enough to optimize their parameters,” Erickson says. “If those schedules are already set up, and you have a special meeting, you can override the schedule for the school that needs to be open for that meeting. In case of an ice storm or other extreme weather event that closes all of the schools, the system can reduce every school to its minimum level of energy consumption.”
The trouble-shooting capabilities of Tracer ES allow a maintenance person who is away from his desk to receive a pager alarm, access the system, display relevant data for the specific piece of equipment, identify the problem, and remedy it quickly.
Previously, a maintenance person might be working on a piece of equipment somewhere, receive a comfort complaint call, and drive back to his office to access a computer only to find that the problem was in the same building where he had been when the complaint reached him. “By providing better accessibility to the system and by improving the workers’ troubleshooting capabilities, Tracer ES has enhanced the productivity of the facilities and maintenance staff,” Erickson says.
Why Wireless?
Another Tracer ES installation, in Trane’s new Grand Rapids, MI, sales center for Michigan’s western lower peninsula district, combines the software’s macro level of control with Wireless Zone Sensors that control HVAC and lighting in individual rooms or comfort zones.
In a study of wireless networks, the Frost & Sullivan research firm has predicted that by 2008 half of the sensors in HVAC systems will be wireless. “Wireless is exploding across all segments,” says Jim Kohl, a senior product manager for Trane Commercial Systems in St. Paul. “It makes sense for building automation. We see it especially in buildings where most commercial and public space already has Wi-Fi (wireless fidelity).”
Kohl cites several reasons for the popularity of wireless sensors:
- They save on installation time and expense, eliminating the need for wiring diagrams, wire, conduit, and electrician fees. “Installing a wired sensor in a typical building could take an hour or two,” he says. “Wireless takes a quarter of the time.”
- They are easy to relocate to meet changing layout needs. “Sensors are moved more frequently than any other device,” he says. “You have labor savings every time you want to move a sensor. Wireless sensors are ideal for spaces with a lot of churn, such as retail and commercial spaces where walls are moved a lot, and for spaces with high installation costs, such as historic brick or stone properties and high-profile spaces with lots of glass where routing wires is almost impossible.”
- They can be mounted where they are needed to maximize the building’s operating efficiency and comfort. “In the construction cycle,” he says, “the sensors go in first, then all the other stuff goes in later. A sensor may wind up in a draft, or too close to a window where the sun streams in, or near something that generates heat and throws off the temperature, such as a coffee pot, stove, computer, or copying machine. You don’t always know. If you want to put a kitchenette there later, you just move the sensor, at almost no cost.”
Kevin Hubert, a building automation systems account sales representative in the Grand Rapids sales center, says the wireless sensor equipment is more costly than the equipment for a wired sensor system, “but installation is so much more economical that it just about makes up the difference, and then you have advantages of wireless for the building owner.”
Constant and Variable
Move-in at the new sales center took place between Christmas of 2005 and New Year’s Day of 2006. The 90,000-square-foot building includes a large warehouse area with 70,000 square feet of storage, service, and shop facilities, plus 20,000 square feet of office space controlled by 20 wireless sensors—an average of 1,000 square feet per sensor, though the control zones vary somewhat in size. (In general, Kohl says, a single sensor could control up to several thousand square feet of open office space.)
“The Grand Rapids sales center’s office portion has a main floor and mezzanine, with the vast majority of the space devoted to sales,” says Hubert. “Eleven rooftop-mounted Trane Precedent 460-volt, 60-cycle, three-phase HVAC units blow warm or cold air into the office space. There is also a Munchkin hot-water boiler for floor radiant heat and sidewalk snowmelt.”
Nine of the HVAC units are constant-volume units, each with a wireless sensor and receiver supplying cubicles within a single comfort zone. The other two are VAV (variable air volume) units—one supplying five executive offices in the building’s interior, the other supplying six conference and breakout rooms.
Each VAV unit has a long duct with branches leading to individual VAV boxes, each of which supplies a room. A wireless sensor in a given room detects the temperature there and tells the VAV box how much air to release to maintain the room’s appropriate temperature.
“The VAV rooftop units provide air at the same temperature all the time,” Hubert says. “Typically, it’s cool air. A pressure sensor in the duct of each VAV unit detects pressure changes within the duct, and the VAV unit’s fan responds by pumping in more or less air to return the duct pressure to the desired level.”
Manual Override
Each wireless sensor communicates through its own receiver with the central Tracer ES control system, which is programmed with separate settings for times when a given space is occupied or unoccupied.
“In a commercial space at 6 PM, the control network would turn the lights off and not control the temperature closely—but sometimes people working late need the lights on and a more comfortable working environment,” Kohl explains. “They can press the ‘occupied’ pushbutton on the sensor to notify the control network.
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| Each wireless sensor communicates through its own receiver with the central Tracer ES control system, which is programmed with separate settings for times when a given space is occupied or unoccupied. |
“The facility manager can set the control system for the length of time an override lasts, and the length of time afterwards that the lights blink a warning before they go out. If a user is still there, he can press the ‘occupied’ button again. When he’s ready to leave, he can press the ‘unoccupied’ button and exit while the lights are blinking. If the last person doesn’t press the ‘unoccupied’ button before leaving, at the end of the override period the lights will go out automatically and the temperature will readjust.”
The wireless sensors also have a thumb wheel that allows occupants of a space to adjust its temperature set point between 50°F and 85°F—or at least to think that they can. The occupants may have only two or three degrees of temperature control if that’s all the flexibility the facility manager gives them.
“You can turn the wheel down to 70°F, but it may not go down to 70°F,” Kohl says. “There’s still a perception that the occupant has control, but unlike a thermostat that tells the air conditioner or furnace to go on and off, the sensor sends the information to a unit control or to a building control system that decides what to do with the information.”
Plenum-Rated Plastic
A Wireless Zone Sensor is 4.78 inches high, 2.90 inches wide, and extends only 1.08 inches out from the wall—low-profile dimensions that are architecturally compatible with those of switchplates for light switches. The device can be screwed into mounting holes in a wall, or attached with Velcro.
The sensing element inside is a thermistor, a diode that responds to variations in temperature with a change in resistance. The thermistor transmits its changes in resistance value via an analog signal to a circuit board, which reads, interprets, and converts the information into a digital signal for transmission to the receiver. The receiver then converts that digital signal back into a resistance value to control the HVAC unit
The most common receiver location is in the plenum (the space between the suspended ceiling and the structural ceiling or roof deck above) of its sensor’s room or zone, though a receiver also may be located in a basement or equipment room near its corresponding sensor.
The sensor and receiver are made of plenum-rated plastic designed for RoHs (lead-free) compliance. Because return air often travels through an egg-crate grate in the ceiling into the plenum and then back into the HVAC unit, materials potentially affecting the air in that space must be plenum-rated so they don’t give off acrid or poisonous fumes in a fire.
Wiring links the receiver to the HVAC unit it controls. Installation involves setting the receiver in place and plugging in both ends of the wire, but Trane sells fan coils and VAV boxes with a factory-installed receiver, eliminating even those steps.
Radio Transceiver
Within a typical building, the sensor’s ideal transmission range is up to 75 feet, but it may work at up to 200 feet. Its maximum obstruction-free line-of-sight range is 1,000 feet. Both the sensor and receiver are transceivers, capable of sending and receiving information. Their ability to exchange and confirm messages “makes sure the network stays robust,” Kohl explains.
They use radio frequencies in the 2.4 GHz band (based on the IEEE 802.15.4 standard), which is specifically designed for sensor networks. “It’s ideal for the application,” Kohl says. “It doesn’t convey a lot of information, but it has a long range and consumes very little power. We’ve set up the software to choose the best channel for communication with the greatest reliability and least interference with other wireless devices. The receiver listens, selects the best channel, and tells the sensor what channel to use. Then the sensor transmits on that channel.”
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| System users may include facility managers and maintenance staff alike. |
A radio or laptop computer can’t listen in on the conversations between these sensors and their receivers, but that isn’t a problem, Kohl says. “This technology isn’t common. It doesn’t have same level of security as Wi-Fi, but it’s a totally separate system. The data it’s carrying is nothing anybody would want, unless you’re interested in the temperature of our space.”
To achieve compatibility, the sensor and receiver must have matching addresses. “We have 999 addresses available for each set,” Kohl says. “We set them with rotary switches that are easy to turn, from 0 to 9, like a combination lock. A sensor and receiver pair come with their addresses preset.”
Batteries Off The Shelf
The sensor uses two AA lithium camera batteries, available off the shelf at a local drug store or gas station. They resemble batteries for a pen flashlight, last up to five years, and cost less than $5 to replace. A pushbutton on the bottom of a sensor lets a building’s maintenance personnel test its battery’s charge and signal strength.
“Sleep mode is critical to the life of the battery,” Kohl says. “Most of the time the sensor is sleeping. Its average power draw is less than the leakage rate of the battery.”
The sensor comes with batteries installed, and its address already set to match that of the receiver. The installer pulls an insulator out from between the batteries. They automatically associate with each other, and the sensor talks to the receiver, telling it, “This is the temperature in my space.”
A sensor’s location has a great deal to do with the comfort level in its space. “The ideal location is the average, the most representative spot for any given zone,” Kohl says. “Inherently, that gives you lower temperature swings and lower consumption on the HVAC equipment side.”
Emergency Generator
The Grand Rapids building normally runs on grid electric power from Consumers Energy Co., a subsidiary of CMS Energy Corp. in Jackson, MI. When grid power is lost, a Generac Model OE6219 emergency generator from Generac Power Systems Inc., of Waukesha, WI, automatically picks up the load for critical systems.
The 11-kW natural-gas-fired generator can run computers, telephones, emergency lighting, and the Tracer ES facility-management system that controls the building’s internal climate, but the HVAC units themselves don’t operate on backup power. “We don’t ventilate if we’re down for any length of time. That’s not a critical service,” Hubert says.