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| What is Demand Control Ventilation? | |||||||||
| Would anybody let the shower at home run all day in case somebody at any time would like to take a shower? And so for ventilation: Better and more economical to ventilate when and where demands are. Many buildings have a CAV ventilation system where the control system is designed with «showers running» all day. Constant Air Volume (CAV) ventilation with clock control is less expensive to install but yields twice the running expenses compared to Demand Control Ventilation (DCV). This is well documented in numerous scientific reports and studies, and applies to buildings in all climate zones worldwide. | |||||||||
| Energy savings with DCV depend on sensor quality | |||||||||
| Sensors for CO2 and temperature are the most critical components in a Demand Control Ventilation system. The motorized dampers are controlled by information from the CO2 sensors, and that control parameter has to be trustworthy and reliable in order for the system to work efficiently. As shown at the bottom of this page by illustrations from a DCV system, this IAQ control only varies within a narrow span of 200 ppm or less of CO2 between ventilation on & off. |
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| The caption above shows CO2 levels in 8 classrooms in a Norwegian school during a normal day, with ventilation running at constant volume (CAV) throughout the working day (clock control). As can be seen, large variations exist in CO2 levels between the different classrooms. Those differences in CO2 levels are caused by variations in occupancy. At times some rooms are overventilated while others experience bad IAQ well above 1000 ppm of CO2. The caption below shows CO2 levels in those same 8 classrooms as above, but now with ventilation only on demand (DCV). As shown by the graphs, CO2 levels are now more even and generally lower than with CAV, with overall IAQ improvements. In addition, DVC operation reduced the HVAC energy consumption by more than 50 % compared to CAV. The CO2 graphs for individual classrooms show that CO2 levels in a DCV system vary only within a narrow span of typically 200 ppm. CO2 sensors therefore need to be chosen on the basis of intrinsically stable calibration and absolute accuracy well inside 50 ppm. |
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