Innovations in Comfort, Efficiency, and Safety Solutions.
Addressing the Retrofit Need
A Commissioning-Friendly, Battery Powered, Wireless CO2 Transmitter (WiFi)
VP of Marketing and Business Development
AirTest Technologies Inc.
The Case For CO2 DCV
Demand controlled ventilation (DCV) offers great potential for energy savings and better moisture control in buildings by modulating outside air ventilation to building spaces based on actual occupancy. This technology offers great potential for savings in retrofit applications. For example a study of 100 commercial buildings by the US EPA found that the majority (83%) of buildings were ventilated well over the ventilation standard of 20 cfm/person with average ventilation rates being 29.8 cfm based on design occupancy (Ventilation Design And Performance In US Office Buildings, ASHRAE Journal, April 2005)
Use of CO2 sensors for ventilation control in these buildings would eliminate this over-ventilation by providing a real time control feedback to ensure that the appropriate ventilation level in these buildings is maintained based on actual occupancy.
The savings delivered from DCV can be significant, particularly for higher density applications with variable occupancy such as schools, retail stores and malls, hospitality venues, auditoriums and meeting spaces. Airtest actually offers a free excel-based tool that allows you to determine potential CO2 DCV savings based on engineered weather data for over 200 locations throughout North America. A number of utilities have actually used this program as a basis for calculating rebates for CO2 DCV. The program is available here: https://airtest.com/support/energy-analysis/co2energyanalysis.php. Typical savings can be 15% to 40% of heating and cooling costs and can amount to thousands of dollars for many building types.
While CO2 transmitter cost is generally well below $200, the cost of
installation in a retrofit application can be five to 15 times the cost
the sensor, all related to wiring and integration with the existing
building control system. This can push energy savings paybacks out
beyond four and five years for some applications. With the
of most of the installation cost, there becomes a much greater
opportunity for CO2 DCV retrofits.
A WiFi CO2 Transmitter Designed for Retrofit Applications
While the wireless application of a wide variety of sensors has
occurred in the building control industry, the power consumption
problem has held back CO2 sensing and control. AirTest has a
great interest in reducing the total installed cost for a CO2 sensor in
order to allow building owners to reap maximum payback in energy
savings. As a result we have developed the TR9299-WiFi, the
first battery powered WiFi CO2 and temperature transmitter using
an LED-based CO2 sensor platform that consumes less than 1% of
the energy of a conventional CO2 sensor. The incremental per unit
cost of incorporating a wireless capability into the CO2
transmitterdesign, is a fraction of the wired installation cost per
sensor, and allows integration of the sensor with the most widespread,
well established, and dependable wireless technology used today…
WiFi. Soon to come are versions targeting Zigbee Pro and
EnOcean communication platforms.
The TR9299 is designed to have a battery life of approximately three years on two AA lithium batteries (sampling every two minutes and broadcasting every 10 minutes). For building operators who are not excited about changing out batteries ever, the transmitter can also be low voltage powered (5-24 VAC/VDC). The TR9299 also has an on-board data logger capable of storing over 3,000 measurement points, which will make it ideal for some temporary measurement applications. An on board visual and audio indicator can also be activated to warn of elevated levels if desired (i.e. LEED credits for IAQ monitoring). The transmitter also features a background auto calibration function that can be activated via a plug-in PC user interface. Further technical details on the product can be found here: http://www.airtest.com/support/datasheet/TR9299wifi.pdf.
Versions of the transmitter are also available to measure:
All WiFi transmitters are designed to offer significant versatility on
how the WiFi communication capability is used.
A Commissioning Friendly CO2 Transmitter
have been selling CO2 sensors and transmitters for over 10 years
and one of the biggest concerns we heard recently is that CO2
transmitters are not “Commissioning Friendly”. Basically, sensors
have been designed to be factory calibrated and end users have been
discouraged from trying to adjust the sensors in the field because
field calibration can be subject to all kinds of variables that could
cause significant error in the calibration process. This has
caused a significant problem for commissioning agents, who are
responsible for verifying sensor operation and readings. It is
often also a headache for contractors who need the commissioning
agent’s report to get paid. Because the sensor elements are
embedded in larger enclosures there is no easy way to verify readings
except by comparing with a calibrated portable device in the immediate
area of the sensor.
It is important to note that the TR9299 does have a background calibration feature that can be activated and even customized by the user. User inputs include the ability to set the background concentration used for calibration, the interval that should be used to sample background concentrations, and the ability to program a quick initial background calibration that occurs soon after initial power up.
In designing the TR9299-Wifi thought carefully about how to make commissioning fast, non-complicated and accurate. We have developed two approaches that we think considerably enhance the commissioning process.
interface for the TR9299
CO2 Demand Controlled Ventilation can save considerable energy in buildings by regulating fresh air ventilation based on actual occupancy. However, the payback of installing these sensors can be considerably lengthened in retrofit applications where the cost of wiring and integrating CO2 can be 5 to 15 times the cost of the CO2 Transmitter. Due to a breakthrough in the design of infrared LED technology, the power consumption of CO2 sensors can be reduced by up to 99% making battery powered, wireless sensors possible. Temperature generation by the sensor that can affect the readings of nearby humidity and temperature sensors is also eliminated.
The AirTest CO2 transmitter design also provides a “Commissioning
Friendly” feature set that allows for a wide variety of methods to
quickly and accurately verify or perform a calibration. Following
the production roll out of the TR9299-WiFi transmitter in May of this
year will be versions designed for other wireless protocols including
ZigBee Pro and EnOcean.
About the Author
Schell is VP of Marketing and Business Development for AirTest
Technologies Inc. a Canadian company that offers a wide variety of
sensor technologies for buildings. Mike has extensive experience in
sensor technologies and building control, and was a co-founder of the
first company to market low cost CO2 sensors for Demand Controlled
Ventilation. Mike was instrumental in ensuring the acceptance of
this innovative technology by today’s codes and standards.
He has authored over 70 articles and papers on indoor air quality,
building science and environmental control.
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