Demand Controlled Systems With Fuzzy Controllers to
Maintain Indoor Air Quality - An Energy Saving Approach
SA Grace1,
D Mohan Lal1 and C Sharmeela2
1
Dept. of Mechanical Engineering, Anna University, Chennai, India.
2
School of Electrical and Electronics Engineering, Anna University,
Chennai, India.
Order Paper
£3.50 (offer only available from this site)
Abstract
The term air conditioning
not only prescribes comfort temperature and relative humidity, but also
the quality of air inside the room. Indoor Air Quality (IAQ) has become a
concomitant of air conditioning. The pollutants generated inside the room
affect the quality of air inside the room. The major pollutants considered
are occupant generated (carbon dioxide - CO2, odour), sulphur
dioxide and toluene etc. The monitoring and controlling of all pollutants
is cumbersome. Of all, CO2 is frequently considered as the
surrogate index of pollutants provided that there are no other major
sources of adverse pollutants present. ASHRAE standard 62-1999 recommends
a ventilation rate of 8 L/s per person. Because carbon dioxide is a
bioeffluent, the monitoring of CO2 concentration inside a space
helps in ventilation control, thereby maintaining IAQ and, in turn,
comfort conditions. Therefore, to achieve this in optimal system design
and control, the instantaneous occupancy level is required. To estimate
the instantaneous occupancy level, the instantaneous CO2
concentration and its generation rate must be known. The impasse with CO2
as an indicator of occupancy is the cost and the time response of the
sensor. Furthermore, the system behaviour is non-linear. These factors
call for more accurate design of controllers. Hence fuzzy controllers can
be chosen as the best option. Not only the ventilation flow rate but also
the supply flow rate can be varied to achieve optimum comfort control from
the system. It has been found that the system settling time is very much
improved when using a fuzzy controller as opposed to conventional
controllers. This enables fast varying occupancy levels to be monitored
for the optimum control of ventilation to maintain IAQ. The regulation of
supply and ventilation flow rates is also shown to be able to reduce fresh
air demand by over 50% when compared to an unregulated system. Apart from
the resultant energy savings achieved in the provision of fresh air, the
air conditioning load is also reduced.
Key words:
demand controlled ventilation, fuzzy control, air-conditioning
systems, energy savings, indoor air quality.
|
