CO2 and radon based dual-mode demand control ventilation strategy.

A dual-mode demand control ventilation strategy was developed targeting at using in institutional or similar buildings where the number of occupants varies frequently. One occupant-related and one non-occupant-related indoor contaminants were used as the indication signals to control the fresh air intake. The first contaminant is carbon dioxide, which is a good surrogate gas for bio-effluent and the second is radon which is non-occupant-related and had been identified as a major indoor air pollutant in some buildings in the university where this project has been carried out. A modulation mode was designed to modulate the fresh air intake to maintain an acceptable indoor air quality during occupied hours. Two purging sequences were designed to reduce the radon accumulation during the non-occupied period, which is the most common reason that the occupants are exposed to an undesired radon level. In order to verify the performance of this dual-mode demand control ventilation strategy, a demand control system was developed and was used in a lecture theatre at the Hong Kong University of Science and Technology, where radon level was found to be very high in our former experiments. A series of experiments were conducted under different occupancy levels and different weather situations. Both the indoor air quality and the energy consumption were studied in these experiments. The experimental results showed that an acceptable indoor air quality could be obtained by this dual-mode demand control ventilation strategy. Comparing with the original fixed-rate ventilation control strategy, about 8.3%~28.3% of the daily electrical energy could be saved.