Suitability of coupling a solar powered ejection cycle with a vapour compression refrigerating machine

The most commonly employed technology for cold production is vapour compression, mainly due to the high efficiency of such devices. However, a major operating issue is the strong dependency of system efficiency and capacity on ambient temperature, which in turn leads to low yearly performance and to a low capacity factor.On the other hand, solar cooling is gaining an increasing appeal as a way to locally exploit renewable energy sources and reducing carbon footprint. Many thermally driven systems are being currently studied, among these the ejection reverse cycle is being proposed as an interesting alternative due to its simplicity, low cost and reliability.The present paper aims to analyse a complex system in which the solar powered ejection machine is used to increase the efficiency of a traditional vapour compression machine by subtracting heat from the condenser. By means of a transient analysis, performed with a reference building and with climate data corresponding to four different system locations worldwide, the year-round performance of such a system in a space cooling application is estimated in terms of energy balance and savings on power costs with respect to the traditional solutions, in order to evaluate its potential benefits and to highlight some issues related to system design and operation. A sensitivity analysis is also performed with respect to solar collector area and equipment sizing, showing how the latter is an important optimisation parameter when designing the system.

► Solar powered cascade system (ejection and vapour compression) analysed.
► Sensitivity analysis to location and some design parameters performed.
► Year-round transient analysis with local weather conditions and reference building.
► Cascade performs better than ejection alone especially for very hot climates.
► Cascade with 20 m2 collectors allows up to 37% power saving (about 1000 kW h/year).