A novel solar-assisted air-conditioner system for energy savings with performance enhancement

This paper presents an effective technique to enhance the performance of a newly-developed direct expansion air conditioner when combining with a vacuum solar collector that is installed after the compressor. In this approach, a novel configuration including a by-pass line together with a three way proportional control valve is proposed in discharge line after the compressor in order to control the refrigerant flow rate. In this design, the refrigerant flow rate is controlled as a function of the refrigerant temperature leaving the compressor, the refrigerant temperature leaving the solar storage tank and the ambient dry-bulb temperature. A generalized optimization algorithm is developed using sequential quadratic programming (SQR) along with a proposed empirical model for the objective function. The key challenge is to estimate the optimum refrigerant temperature entering the condenser in the new design. The optimization algorithm is simulated in a transient simulation tool to predict the optimum set-points of refrigerant temperature entering the condenser, and then implemented as a reference for an on-line closed-loop controller. The system under investigation is extensively equipped with a number of instrumentation devices for data logging. The benefits of the new design lie in the fact that the new designed system operates at a higher subcool temperature after the air-cooled condenser which significantly result in increasing the overall system coefficient of performance. © 2012 The Authors