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October 7, 2011 -
Today's tip from Building Operating Management comes from Angela Cremeans and R. Stephen Spinazzola of RTKL: In spaces that have widely varying levels of occupancy, demand control ventilation can reduce energy use and costs.
Many spaces are unoccupied for significant stretches of time, including churches, auditoriums, offices and retail spaces. Despite that fact, most HVAC systems are designed to bring in the same level of outside air continuously. But if a space is unoccupied, heating, cooling and moving outside air to that space can waste a significant amount of energy and money.
Demand control ventilation is a sophisticated strategy that supplies outside air to a space only when it is needed. Demand control ventilation relies on the fact that people in a space produce carbon dioxide. Sensors measure carbon dioxide levels. As those levels rise, more outside air is brought into that space. If levels fall, the amount of outside air is reduced, cutting the cost of conditioning and moving outside air. The amount of air is tailored to the specific needs of a given zone.
In a demand control ventilation strategy, the level of carbon dioxide is taken as a general indicator of the level of other contaminants. By increasing the amount of outdoor air brought into a space when carbon dioxide levels rise, the concentration of those other contaminants is reduced, improving indoor air quality.
Demand control ventilation can save energy costs in three ways:
1. Less outdoor air has to be conditioned by the HVAC system, so heating or cooling system energy is saved.
2. Less air has to be moved, so fan energy is saved.
3. If a building has a heat recovery system using building exhaust, that can further reduce the amount of energy consumed.