Outdoor Carbon Dioxide Measurements for Demand Controlled Ventilation
www.vaisala.com Outdoor Carbon Dioxide Measurements for Demand Controlled Ventilation The outdoor CO2 level serves as a baseline for comparison to indoor CO2 concentration. The outdoor CO2 level directly impacts indoor conditions-if the outdoor CO2 concentration level is 500 ppm, it is rarely lower indoors. Selecting an accurate outdoor CO2 instrument is crucial for monitoring outdoor levels. Demand controlled ventilation (DCV) helps to maintain good indoor air quality while optimizing energy consumption. In a typical set-up only indoor CO2 levels are measured. Ventilation controls are operated based on the assumed outdoor CO2 level of 400 ppm. However, locally elevated CO2 levels occur due to CO2 emissions from transportation, energy production and industrial manufacturing. Ventilation guidelines, such as ASHRAE, recommend indoor CO2 levels not to exceed the surrounding outdoor concentration by 600 ppm. Also, LEED guidelines suggest providing an alarm when the indoor CO2 level exceeds the outdoor level by 530 ppm, or 1,000 ppm absolute. Reliable correlation between indoor and outdoor CO2 levels can only be achieved by measuring both. Measuring CO2 Outdoors Knowing outdoor CO2 levels helps when assessing indoor conditions. During periods when the outdoor CO2 level exceeds 400 ppm the space may be over-ventilated. In order to truly optimize energy consumption, outdoor CO2 concentration should be measured. The real time differential between indoor and outdoor CO2 concentration can be used as a control parameter. High accuracy of the outdoor CO2 instrument is important. Typical indoor CO2 instrument accuracy of ±50 ppm is just not enough for a true reference. The outdoor instrument should have an accuracy equivalent to or better than ±2% of reading for efficient real time CO2 differential control. Moreover, as there are large diurnal and seasonal variations in outdoor temperature, the outdoor CO2 instrument should automatically compensate for temperature variations. Vaisala CARBOCAP ® Carbon Dioxide Probe GMP343 for Outdoor Measurements: Outdoor CO2 sensors need to operate in varying conditions. They have to tolerate rain, hail, snow, solar radiation, dirt and dust, as well as temperature extremes between -40 and +60 °C (-40 ... +140 °F). Vaisala CARBOCAP® Carbon Dioxide Probe GMP343 has been specially designed to take outdoor measurements, with: • Accuracy of ±(3 ppm + 1 % of reading) at 25 °C (77 °F) • IP65/IP66 housing classification for harsh environments • Operating temperature range -40 ... +60 °C (-40 ... +140 °F) • Low maintenance need due to highly stable CARBOCAP® sensor with built-in reference measurement • Automatic compensation of CO2 readings for temperature variations • Possibility to compensate for pressure (site elevation) Please contact us at www.vaisala.com/requestinfo www.vaisala.com Ref. B211381EN-A ©Vaisala 2014 Scan the code for more information This material is subject to copyright protection, with all copyrights retained by Vaisala and its individual partners. All rights reserved. Any logos and/or product names are trademarks of Vaisala or its individual partners. The reproduction, transfer, distribution or storage of information contained in this brochure in any form without the prior written consent of Vaisala is strictly prohibited. All specifications — technical included — are subject to change without notice.
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