Modeling and Control of an Energy-Efficient Hybrid Solar-Assisted Air Conditioning System

This paper addresses the modeling and control problem of a newly-developed hybrid solar-assisted air conditioning system for improved energy efficiency. A 6kW solar-assisted direct expansion air-conditioner is used for experimentation and data collection. To increase sub-cooling of the refrigerant at partial loads, we propose a new discharge bypass line together with an inline solenoid valve, installed after the compressor to regulate the mass flow rate of the refrigerant vapor passing through a hot water storage tank. Additionally, a variable speed drive is coupled with the condenser fan to control the air flow rate and synchronized with the inline valve closing and opening. For the control purpose, a lumped parameter model is first developed to describe the system dynamics in an explicit input-output relationship; then, a linear optimal control scheme is applied for the system's multivariable control. The system has been fully-instrumented to examine its performance under different operation conditions. Numerical algorithms, implemented in a simulation tool, are then employed to predict the energy performance of the system under transient loads. Results show that up to 14% energy savings can be obtained by the proposed system.