Data Center

Mastering the Science (and Art) of Building Control Sensors

We all know the drill. One person in your cubicle farm is either always too cold or too hot and ends up commandeering the thermostat, forcing everyone else to work according to their personal temperature swings and whims. Or maybe there’s one area of your data center where you can never get the temperature quite right.

There’s often a good reason for such events: a poorly designed building control system with poorly placed sensors is the primary culprit.

Sensors are among the most important—yet most easily misunderstood—parts of a building control system. Schneider Electric’s Energy University is here to help, with a new course called “Building Controls II: Control Sensors.” It’s designed not only to help you understand the various forms of sensors used by today’s complex building control systems, but also how to choose the best type and placement to achieve optimal results.

For example, the course details the difference between thermistors and temperature transmitters for specific applications and underscores the easily overlooked issues when designers look to place thermal sensors outside a building to aid in controlling internal temperature.  For example, sensors should never be placed in direct sunlight, since that tends to skew their readings. Thus, buildings located in the northern hemisphere should never place a sensor on the east or west sides of the building, which receive direct sunlight at certain times every day. Instead, they should place the sensor on the north side of the building, which receives the least amount of direct sunlight in a given year.

The course also offers other helpful design tips, including the proper use of control zones to ensure optimal temperature across an entire building floor or within a data center. For example, designers may divvy up control zones, marking one for a cubicle farm in the middle of the floor, another for a row of offices on the sunny south side of the building and another for the work areas surrounding heat emitters like printers, copiers and coffee machines. They can do the same for a data center, differentiating areas densely packed with servers from more open areas.

Each zone has its own temperature requirements, requiring its own sensors and control systems. The result is more efficient heating and cooling—as long as the initial design holds up over time. Unfortunately, many times the designer’s engineering assumptions turn out to be wrong, leaving buildings with poorly placed or missing sensors. In that case, the building’s occupants must learn to live with the system, since the only remedy is to modify the mechanical system, which can get costly fast.

To avoid such mishaps, designers need to take many factors into consideration when placing sensors, including location, nearby equipment, air vents, doors, windows and more. The key is to first observe any heating or cooling impacts to the room, and then place the temperature sensor where it’s most likely to get the truest reading.

In addition to placement, the course outlines the wide variety of sensors available, including temperature, relative humidity, pressure, flow meters, electrical, gas, switches and occupancy sensors. It discusses the importance of placing sensors close enough to the control system to ensure losses due to electrical resistance don’t cause measurement errors. After all, you can’t control efficiently what you can’t measure accurately.

To learn more, sign up for “Building Controls II: Control Sensors.” You’ll find it, along with many others, in the college of Energy Efficiency on the Energy University site. To register for free, simply visit the Energy University site and click the “Join” link.


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