Technology selection essential for DCV savings


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Technology selection essential for DCV savings - 1

/ APPLICATION NOTE NOVEMBER 2009 Technology selection essential for DCV savings Optimizing demand controlled ventilation (DCV) will contribute to an enhanced indoor environment at lower operating costs. The system can only be optimized by accurate carbon dioxide (CO2) sensing. CO2 Highlights Related to DCV Good indoor air quality can be achieved based on occupancy CO2 measurement is the most economical method to monitor both air quality and human presence with one sensor Energy is saved by minimizing use of unconditioned outside air Inadequate ventilation results in an elevated CO2 level, causing drowsiness and decreased productivity CO2 Information CO2 is measured in parts per million (ppm) Typical outdoor ambient CO2 concentrations: 350 – 450 ppm Acceptable IAQ CO2 concentrations: 600 – 800 ppm Tolerable IAQ CO2 concentrations: 1000 ppm Humans spend 90 % of their time indoors. Studies indicate that indoor air quality (IAQ) is directly linked to human well-being and productivity. The CO2 level can be used as an indicator for indoor human presense. A high CO2 level is a sign of poor ventilation and often an indication of other unpleasant odors in the air. As many as 30 % of buildings have poor IAQ. The most economical way to determine the ventilation demand is to measure carbon dioxide, which increases in relation to number of humans present. By controlling ventilation according to the CO2 level rather than the assumed amount of people occupying the space, the indoor air can be kept fresh without over-ventilating and wasting energy. Industry drivers Limits for CO2 levels in indoor air differ slightly from one country to another. For example, interpretation of ASHRAE ( 62.1 “Ventilation for Acceptable Indoor Air Quality” implies CO2 levels should not exceed 700 ppm above outdoor ambient levels of 400 ppm. The EU Commission has issued an Energy Performance in Buildings Directive (2002/91/EC) which specifies that energy savings should not have a negative impact on indoor air quality. Energy savings as stated by the ETIAQ (Energy Technologies and Indoor Air Quality) project coordinated by Rehva, the Federation of European HVAC Associations, reports 20-50 % energy savings in public buildings using DCV, and even greater savings potential in buildings with varying occupancy.

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