Not even five years ago, engineers routinely complained about the inaccuracy of sensors and controls, especially CO2 sensors. Those devices were basically called a waste of time. Or, as one frustrated engineer called them, "a major headache."

Then "something" happened. The technology was refined, and they started becoming more reliable. Readings became more accurate, there was no longer a need to recalibrate every three to six months, and costs started coming down. Engineers discovered that CO2 sensors could, indeed, deliver on their promises to help regulate ventilation, saving energy and providing more comfort in the process.

Even regular old temperature sensors have become more reliable. Although never as "flaky" as the CO2 sensors were considered to be, they have been improved. Some say they've become almost too sensitive, while others state that their increased sensitivity helps provide more comfort. Fortunately, lower costs are allowing engineers to sprinkle many more of these sensors around a building, allowing much tighter control of the occupied space than they could achieve previously.



CO2 sensors, like the one shown in this office space, are being put to use for ventilation controls. (Photo courtesy of Engelhard Sensors.)

Big Improvements

One of the most significant developments in control and sensor technology in the last five years is the increased availability of low-cost microprocessors. These have allowed sensors to become much more intelligent. Many times sensors can now perform multiple tasks, such as sense temperature and humidity. Many of the smarter sensors also have a built-in "checks-and-balances" feature, which allows them to determine whether or not a correction is really necessary.

"In our devices, we have two channels: one looks at the infrared absorption of the gas we're measuring, and the second looks at the neutral wavelength where there's no change in the gas," explains Mike Schell, director of marketing and business development for Engelhard Sensors (Goleta, CA). "By comparing the two, the sensor can see if there's a change in the concentration of gas or whether it's just a change due to some other factor."

Another benefit to using microprocessors is that recalibration becomes much easier. If recalibration is necessary, some sensors "know" it and can recalibrate themselves. In the case of Engelhard Sensors, there's a built-in algorithm, which self-calibrates the unit.

Luci Keazer, P.E., control systems engineer at Purdue University (West Lafayette, IN), says that recalibration of CO2 sensors in particular is much faster than it used to be.

"The calibration and user-friendliness of CO2 sensors has improved immensely," she says. "It just takes a couple of minutes to check the calibration or recalibrate them. Some of them only need recalibration every five years."

She adds that CO2 sensor technology has finally developed to a point where the sensors can be used practically.

"Five years ago they were more of a headache and a maintenance issue. They've become more accurate, more stable, and there's less drift," she says.

Now she uses the sensors in large lecture rooms that are served by one air handler. She says that once she gains more confidence that the technology is working well - and if the price comes down a little more - she'd like to start using CO2 sensors at room level control.



Business Is Booming

Keazer is not the only one making use of CO2 sensors. Manufacturers state that their business is growing rapidly. Dave Weigel, P.E., product manager for Kele & Associates (Memphis, TN), says there's been a "healthy amount of growth" in his business.

"But the growth in sales of carbon dioxide sensing is outstripping the growth rate of everything else," says Weigel. "People are using that for demand-controlled ventilation in buildings to save energy and still maintain good indoor air quality."

ASHRAE Standard 62-89 is certainly one of the reasons why people are using CO2 sensors for ventilation control, but the other reason is litigation.

"While people use the sensors for IAQ purposes, sick building syndrome (SBS) lawsuits are the main reason why the focus is on CO2 and air quality sensors in general," says Mike Drury, co-owner of Automation Components Inc. (Middleton, WI).

Drury adds that his company does a large portion of its work overseas, particularly in the Pacific Rim. That area has been utilizing CO and CO2 sensor technology for years. Thanks to Standard 62-89 and litigation, though, the United States is starting to catch up to the rest of the world.

One advocate of CO2 sensors is Dennis Kerlin, chief engineer at Harley-Davidson (Milwaukee). He uses the sensors for several reasons. First, the sensors help him keep from overventilating his 230,000-sq-ft complex.

"If you're overventilating, you're using more mechanical cooling," he says. "We can maintain good CO2 levels without overventilating the space, which costs more money."

The second reason he likes the CO2 sensors is that it puts workers' minds at ease: The CO2 sensors have remote displays for employees to see.

"Occupants have enough to worry about in the course of a day without having to be concerned about their comfort," says Kerlin. "People have a tendency to be less productive if they're uncomfortable." Keazer notes that CO2 sensors are an extremely smart technology.

"Measuring the CO2 is a terrific indicator of the number of people in a space," he says. "It makes so much sense to use that and then when you don't need the ventilation for full capacity, you close it down to a nominal percentage. You can stop conditioning a lot of outside air that might be very hot or very cold and save a lot of energy."



Energy Efficiency Or Comfort: Do You Have To Choose?

Whether controls and sensors are used more for energy efficiency or comfort really depends on who you're speaking to. Manufacturers often say that it's easier to sell a control or sensor based on the energy savings it will help the owner achieve. Most engineers say that controls and sensors are used to provide more comfort within a space.

Bob Gladney, P.E., associate with Clark-Nexsen (Norfolk, VA), says that comfort is extremely important today.

"One of the big complaints in office buildings is comfort," he says. "Tenants want to be comfortable, and they're going to look for a comfortable building in which to do their business."

He does add that energy efficiency is always a goal of building owners because of the dollars involved in operating a facility.

Charles Brown, P.E., senior mechanical engineer at Clark-Nexsen, notes that it costs $1.50/sq ft to run an hvac system in a building, but it costs $25/sq ft to keep an employee.

"That's the slant we see put on it - it's very important that people remain comfortable and productive. Of course, you have to do it as efficiently as possible," says Brown.

Engelhard's Schell says that in most applications today, comfort only relates to temperature, and most buildings can control temperature fairly well.

"It's still really hard for building owners to economically justify adding more sensor technology to increase comfort. Issues of better air quality bring visions of productivity and well-being and general comfort, but it is difficult to judge the economic impact. The challenge is to provide comfort, enhance air quality, and save energy. That's what sells."

The key is finding a balance between energy efficiency and comfort, and that will vary from building to building. Kerlin notes that in the beginning, he primarily used controls and sensors to just save energy. "Unfortunately, we had to give up comfort levels, so we went back to taking care of our people, because the little you save on kW, you lose in productivity," says Kerlin. "We'll keep everybody as comfortable as we can whenever we can, but we're still being conscious and squeezing out every little bit on the energy consumption side as we can."



Everything At The Touch Of A Button

Not that long ago, it seemed outrageous to think of a building in which controls and sensors detected every condition and relayed that information back to a central building automation system (bas). An engineer sitting at a terminal in the mechanical room could see what was happening in every nook and cranny of a building and make adjustments right from his seat.

That's becoming more of a reality thanks to the smarter sensor technology on the market. Reduced costs (while still not reduced enough for some) have meant more sensors placed around a facility, and improved building automation systems can interpret the information they're receiving from the sensors and notify the engineer of any problems.

Expect to see the "whole building control" concept even more in the future, especially because the U.S. Government is very interested in this type of totally controlled environment. Currently the National Institute of Standards and Technology (NIST) is working hard to create a cybernetic building system (CBS). (A CBS is defined as a multi-system configuration that is able to communicate information and control functions simultaneously and seamlessly at multiple levels.) Obviously, controls and sensors will be a big part of the project, which is why NIST is partnering with various controls manufacturers to make its cybernetic building a reality.

NIST says that its cybernetic building system will involve energy management, fire detection, security, and transport systems, as well as information and complex control at many different levels. One of its main goals is to develop advanced measurement technologies, including smart multi-functional sensors and wireless sensor networks.

Keazer is one who says that wireless sensors would certainly alleviate a lot of problems at her facility. "We have a lot of old buildings where maybe it's not easy to run a wire, so there definitely would be applications where we could use a wireless sensor," she says.

In a wireless system, each sensor would have its own cell-phone-like transmitter that would transmit its values via radio waves to a central controller. This would significantly reduce the cost of sensor installation, as it would eliminate the need to run wires all over the building - particularly when a building is being retrofitted. Costs would also be decreased on multiparameter sensors, such as those that detect CO2, temperature, and humidity, because it would be possible to eliminate all wiring except that needed for power.

Schell notes that the technology is available to do this today and it is being used in residential and commercial security systems and some commercial fire and safety systems.

"Unfortunately, the cost is really still too high to justify its use for sensor communication in hvac systems," says Schell. "I would guess that in approximately five years every sensor could actually integrate a wireless communication capability for an added cost of $5 or so."

Keazer does say that many of the new buildings erected on her campus are already somewhat cybernetic. "We can do everything all the way down to room level control, right from our central building automation system," she says.

In many buildings, gone are the days when an engineer had to trudge over to whatever space was too hot or too cold to check out the problem. Kele & Associates' Weigel remembers working as a facility engineer in a hospital. If someone called to say the temperature wasn't right, he'd walk the quarter-mile over to measure the air temperature coming out of the diffusers. If that was warm, he'd have to go back a quarter-mile and down one floor to the air-handling unit to see what was wrong. If the problem was the chilled-water system, he'd have to go down to the basement and find out what was wrong there.

"Today, I could click on my mouse and see all the information on my computer screen without leaving my desk. I could probably correct the problem, too, before anybody would call in the first place," says Weigel. Automation Components' Drury says that controls and sensors have allowed some buildings to come very close to total control.

"For the most part, a building that's fully automated is very efficient and relatively trouble-free in terms of having to scout for problems," he says. "If the installation and the software are done correctly, it's amazing how self-sufficient a building can be."

Catching A Moving Target

Controls and sensors have definitely made big strides in the past few years, allowing more engineers to totally control a building space. Unfortunately, the technology is moving so fast that it's hard to keep up. Keazer notes that it's a challenge to keep Purdue's technicians trained, because they have a variety of controls and sensors and each one requires different maintenance.

In order to keep up with the technology, Gladney says it's necessary for engineers to update themselves frequently.

"Whether you deal with a controls manufacturer or contractor or through literature, engineers need to expose themselves on a daily basis to keep up. Otherwise mistakes will be made."

Brown says that in most engineering firms, one or two people are designated to keep on top of the technology. Those people will act as internal consultants to others in the firm.

"It takes a lot of time, because you have so much more capability with your controls," says Brown. "You can make systems do things that five years ago you could never even consider. It's exciting." And it's bound to get even more exciting as the technology continues to advance exponentially. ES

Interoperability Is Still A Big Issue

Even though sensors and controls are usually tied to a building automation system (bas), their technology does not need to be "BACnet-" or "LonTalk"-compliant. The sensors merely detect certain building conditions, then relay that information to the bas.

However, most of those interviewed pointed out the interoperability issue as their major problem where controls are concerned.

"Standardization needs to move ahead," says Bob Gladney, P.E., associate with Clark-Nexsen (Norfolk, VA). "That's the big problem right now: Actually achieving true open communications between devices and mechanical equipment. The biggest problem we have now is getting equipment and controls to communicate."

He also notes that when standardization becomes a reality, costs will come down because competition will become more intense.

Meanwhile, Luci Keazer, P.E., control systems engineer at Purdue University (West Lafayette, IN), says interoperability is an ongoing challenge with her facility's systems as well.

"We would like to be able to use more than just one system and have them communicate with each other. It's a challenge - a deficiency - to interoperate building control systems."

As noted in the July 1999 issue of Engineered Systems ("Interoperability, Where Art Thou?", page 56), this saga will continue to play out for quite some time.

"We're still struggling with all the interoperability issues," says Charles Brown, P.E., senior mechanical engineer at Clark-Nexsen. "But I think we're going up the learning curve on it. Probably 10 years from now we'll look back and think what we're doing now is kind of strange."

Hmmm. Time will tell, won't it?ES - Joanna R. Turpin