An adaptive controller based dynamic simulation of household air-conditioner with indirect evaporative cooler as dedicated outdoor air system

Abstract

The lack of controllable ventilation design for acceptable indoor air quality is a major problem facing small-scale direct expansion air conditioning (DXAC) systems for household applications. The DXAC-IEC hybrid cooling system, consisting of DXAC systems and indirect evaporative cooler (IEC) ventilators, can provide an energy-efficient solution to this problem. An adaptive controller is proposed in this study to respond to changeable indoor and outdoor disturbances to provide standard-compliant fresh air demand, guarantee indoor thermal comfort and reduce energy consumption at the same time. In the adaptive control scheme, different operation modes are applied by combining three modes of compressor speed (high-low, low-off, off) and three modes of IEC fan speed (high, middle, low) responding to outdoor and indoor conditions. The dynamic performance of DXAC-IEC system on typical days and annual performance were numerically investigated. The results show that considerable energy saving (22.1 % to 34.1 % in Xi’an) can be achieved in transition seasons by DXAC-IEC system for providing standard-compliant ventilation rate and guaranteeing indoor thermal comfort simultaneously compared to a standalone DXAC system. However, extra energy (10.0 % to 25.4 % in Xi’an) will be consumed on summer days. On a typical summer day, the indoor relative humidity will increase by 10 % to 15 % because of extra latent load brought from IEC ventilator compared to the standalone DXAC system, but indoor temperature can be precisely controlled and CO2 concentration is mostly below 1500 ppm.