An enhanced temperature control strategy for energy saving in building air-conditioning system

Abstract

Centralized packaged air conditioning (A/C) systems are widely used in commercial buildings, offices and low-rise residential buildings. Very few research on capacity-load matching capability is carried out for an installed and operational centralized multi-circuit air-conditioning systems and as such, inherent operational characteristics of these systems are not available for retrofitting and design purposes. This research presents an enhanced temperature control strategy that was utilized for the development of a controller for capacity-load matching of a two-circuit water-cooled packaged (WCPU) building A/C system. The dynamic modeling for the two-circuit system was based on data collected from an operating WCPU A/C system of the Industrial Laboratory, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor Bahru using the System Identification procedure. An enhanced temperature control strategy was utilized for the design of the control of two compressor circuits to match the performance of the A/C system with the imposed changing loads in order to maintain a desired room temperature. This strategy involved the combined operation of a variable speed compressor and a constant speed compressor of the two-circuit WCPU system. PID control was utilized for the variable speed compressor while the On/Off control was utilized for the constant speed compressor. The developed models were then used for the deployment of a digital temperature controller referred to as DTPID in the actual WCPU system to replace the conventional On/Off thermostat control. The results indicate that the DTPID controller was able to maintain the desired room temperature demonstrating the capacity-load matching capability of the controller with the enhanced temperature control strategy. The results showed that energy savings of up to 31.8 % was achieved when the conventional On/Off controller was replaced with the DTPID controller for the base case operation of the WCPU system. Average values of the Coefficient of Performance (COP) were determined to be in the range of 3.7 to 4.7 which is within the recommended COP by the MS1525:2014 for water cooled packaged units.