Potentialities and constraints of a novel R152a variable geometry ejector cooling cycle with automated operation driven by solar energy and biomass

This work presents an innovative heat-driven cooling cycle based on a Variable Geometry Ejector (VGE) using R152a as working fluid, able to adjust automatically its internal configuration to variable operating conditions with two degrees of freedom. A prototype of the VGE cooling cycle with a nominal capacity of 5 kW was designed, built, and tested at a laboratory scale. It was then integrated into the HVAC system of a residential building constructed recently in Portugal. The system is fed by solar energy and biomass to drive the ejector cycle, representing the first example of a VGE cooling cycle operating in a real environment. To estimate the potential energy performance of the whole system before the analysis of monitored data, numerical simulations of the integrated building-HVAC system were performed with TRNSYS. The simulation results show how the capability for adjusting the ejector geometry allows for achieving steady efficiency throughout the cooling season, even in severe operating conditions. Even though the VGE cycle demonstrated a thermal performance lower than expected on a seasonal basis, significant exploitation of renewable sources could be achieved. During the summer, electric energy consumption is limited, and more than 80 % of the overall energy input is covered by solar energy and biomass. The paper also investigates the most noticeable constraints of ejector-based cooling systems, showing that the generation and heat dissipation loops must be carefully designed, and the optimal application for this technology, such as its integration in multi-family buildings or gyms/pools to recover the condensation heat for fresh-water pre-heating.