In a university building in Boston, IAQ complaints prompted an increase in outdoor air ventilation, causing a large increase in energy use. C02 readings were then taken in an auditorium, cafeteria, offices, and classrooms. The readings were used to calculate occupancy estimates and to simulate operation of a demand-controlled ventilation (DCV) system. The differential equations were solved in a spreadsheet program using a Runge-Kutta macro. A PID control system was also simulated. Ventilation adjustments were input to DOE-2 to estimate energy savings. A two year payback was estimated.
Demand controlled ventilation systems can be used to minimise energy consumption whilst maintaining satisfactory levels of indoor air quality (IAQ). As an alternative to C02 sensors IAQ sensors (based on Taguchi mixed gas sensors) can be used to infer levels of IAQ. This Technical Note provides details of a series of laboratory and site tests to determine the performance of a range of IAQ sensors.
Entertainment clubs, nightclubs, theaters, restaurants, and coliseums, with their highly variable occupancy rate, are excellent candidates for demand-controlled ventilation. The dynamic thermal requirements of both heating and cooling, coupled with the need to control indoor air quality because of the large number of patrons who also may be smoking during the highest occupancy, provide an opportunity to integrate the temperature controls with an indoor air quality control system.
Many ventilation requirements and recommendations are in the form of outdoor airflow rates per person. Ventilation systems are therefore designed to provide a minimum level of outdoor air based on the designed occupancy level multiplied by the per-person ventilation requirement. Because the indoor generation rate of carbon dioxide is dependent on the number of occupants, it has been proposed to use indoor carbon dioxide concentrations as a means of controlling outdoor air intake based on the actual number of occupants in the space as opposed to the design occupancy.
Ventilation is necessary to provide a good indoor air quality to occupants in office buildings but is however a major energy consumer. In that manner, ventilation in itself can contribute to much more than 50% of the energy consumption for heating in well insulated office buildings. Likewise, the general trend in standards to augment ventilation requirements would still increase its energy costs. Thus, it seems obvious that an intelligent control of ventilation in office building allows to obtain substantial reductions of energy consumption.