Demand Control Ventilation: Lessons from the Field- How to Avoid Common Problems

Acker, Brad; Van Den Wymelenberg, Kevin
May 2011
ASHRAE Transactions;2011, Vol. 117 Issue 1, p502
Academic Journal
Demand control ventilation (DCV) has the potential to save energy by reducing ventilation rates in accordance with occupancy levels provided by the surrogate indication of CO2 levels. However, improperly installed, designed, or operated systems may save energy at the expense of Indoor Air Quality (IAQ) or enhance IAQ at the expense of energy. These outcomes may have the potential to foul the image of an otherwise viable energy efficiency measure. This paper reports what the authors believe to be common problems in the design, installation and operation of DCV systems which use CO2 as a surrogate for occupancy levels. Six HVAC systems were investigated: two commercial offices, two medical offices, and two school environments. The design drawings, air balance reports, and current equipment set up were investigated. Four systems were controlled locally through roof top unit control logic and two systems were controlled by central building energy management systems. Functional testing of equipment was carried out and system parameters were logged including CO2 levels, fans states, and air stream temperatures. Functional testing was broken up into three system aspects. First, CO2 control signal functional testing was conducted to confirm that the control link between CO2 sensors and outside air damper positioning was in place. Second, sensor placement functional testing was conducted to confirm that the sensors placement could accurately report the CO2 levels of the controlled zone. Third, the Outside Air (OSA) level test was conducted by inspecting the air balance reports to determine the OSA rates and to confirm that the system was balanced in accordance with DCV standards. The study found that no systems were functioning properly for a number of reasons, some of which were overlapping. Reasons for non-functionality included poor sensor placement, improper information provided in mechanical schedules or design documents, fan cycling issues, and poor installation. Details on failure modes will be presented. Proper engineering documentation requirements will be explained. Test, Adjust, Balance (TAB) specifications and DCV specific requirements for TAB along with information that building operators need to know about system operation will be presented.


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