Experimental Evaluation of Combined DCV and Economizer Cycle using a FLC Variable Air Volume (VAV) System

Abstract

A healthy indoor environment with sufficient fresh air is a prerequisite for the well-being and high productivity of building occupants. Carbon dioxide (CO2) based Demand Controlled Ventilation (DCV) optimizes and resolves the traditional conflict between reducing ventilation to save energy while maintaining adequate ventilation for air quality. Therefore, in conditioned spaces where occupancy levels vary, CO2based DCV can prove to be an energy efficient method for meeting ventilation needs while maintaining good IAQ. Furthermore, an economizer cycle can be used to save cooling energy. This design scheme takes advantage of cool weather conditions to supplement or satisfy the cooling load. When a Proportional-Integral-Derivative (PID) controller is used, it can respond only to linear variations using single input and single output operations. This can be improved by using a Fuzzy Logic Controller (FLC). This paper deals with the energy savings in a VAV air conditioning system achieved by combining DCV with an air conditioning economizer cycle incorporating FLC. The CO2 concentration and outside temperature are taken as input and damper angle as output for the FLC. Both laboratory measurements and simulations were made. Simulation was undertaken using MATLAB-Simulink. The potential energy savings of DCV combined with a temperature economizer cycle is in the range of 28% to 79% for VAV systems and 19% to 42% for CAV systems. The Indoor Air Quality (IAQ) is also maintained. An experimental test rig was developed and used to verify the performance of the system. This experimental work has been conducted to obtain the system’s response for design outdoor conditions.