HVAC ducts ideal for wireless monitoring

An example of an RFID tag.

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A study led by a North Carolina State University professor has revealed that wireless monitoring technology can be used through the means of a building’s HVAC ducts.

The study will be published in the September proceedings of the Institute of Electrical and Electronics Engineers.

Dr Dan Stancil, professor and head of North Carolina State’s Department of Electrical and Computer Engineering and co-author of the paper, found that the use of HVAC ducts in order to execute wireless monitoring equipment could save building managers and builders both money and time as this technology can be installed without having to route wires throughout their buildings.

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In addition, it can be used to introduce radio-frequency identification (RFID) tag carbon monoxide monitors, smoke detectors or sensors that can detect biological, radiological or chemical agents.

RFID tags have the ability to contain sensors, which transmit information back to a centralised reader in order to collect data from tags with radio antennas. The electronic reader in a RFID system sends a radio wave with a certain frequency, and when the tag receives it, it takes in the energy from that particular transmission and responds to the reader by the means that it reflects the wave.

“Since you can tap into existing infrastructure, I think this technology is has immediate economic viability,” said Stancil. “Avoiding the labour involved with installing traditional sensors and the related wiring would likely more than compensate for the cost of the RFID tags and readers.”

Normally, ultrahigh-frequency (UHF) RFID systems, which function in the 902-928 MHz band in North America, need to be within 5-10 m of the centralised reader for it to be able to respond to transmissions. However, tapping into a building’s HVAC system allows UHF RFID tags to function as far as 30 m away from the reader.

The HVAC ducts in buildings are excellent places for RFID systems because the hollow metal pipes can direct radio waves to and from the reader, maintaining a strong signal because the transmissions will not disperse. The signal may even be strong beyond 30 m, but tests conducted under this study only went up to that distance.