Fuzzy controllers for HVAC-VAV systems to maintain IAQ

The term air conditioning not only prescribes comfort temperature and the relative humidity,but also the quality of air inside the room. Indoor air quality (IAQ) has become a concomitantof air conditioning. The pollutants generated inside the room affect the quality of air inside theroom. The major pollutants considered are CO2, sulfur dioxide, toluene, etc. Monitoring andcontrolling of all the pollutants is cumbersome. CO2 is considered as the surrogate index ofpollutants. Appendix D of the ASHRAE standards 62-1999 recommends a ventilation rate of15 cfm per person. To incorporate this in the optimal system design, the instantaneousoccupancy level is required. It is imperative that the instantaneous CO2 level and thegeneration rates must be known to estimate the instantaneous occupancy level. Thusmeasurement of the CO2 level inside the room is performed by the ventilation control, whichthereby maintains IAQ and in turn the comfort level. The problem with the CO2 as anindicator of occupancy is the accuracy level and the time response of the sensor. Furthermorethe system is non-linear. These factors call for more accurate design of the controllers. So,fuzzy controllers can be chosen as the best option. It has been found that the system settlingtime has been very well improved. This indicates that the fast varying occupancy level can bemonitored and controlled, thereby maintaining the IAQ inside the conditioned space.