Thermal comfort-constrained nonlinear operational optimization of a solar-absorption-radiant cooling system

Abstract

With the increasing demand for sustainable building solutions, especially under extreme weather conditions, there is a growing need for renewable-powered cooling systems that can minimize energy consumption and carbon emissions. Solar-absorption-radiant cooling systems offer a promising alternative to traditional air conditioning systems, but their effectiveness relies on efficient control strategies. This study investigates the optimal control of a solar-absorption-radiant cooling system for a single-story office building using non-linear programming (NLP) to minimize operating costs while maintaining thermal comfort. This is achieved by directly integrating the building model and thermal comfort calculations within the optimization procedure. By incorporating a solar collector, storage tank, assisting boiler, and absorption chiller, the system achieves a solar fraction of 0.8, minimizing daily operating costs to 2.11 USD and carbon emissions to ∼ 39.1 $k{g}_{C{O}_2}$. The system maintains an average PMV of 0.14, an operative temperature of 25.63 °C, and a coefficient of performance of 0.72. The study also explores the impact of varying thermal comfort constraints, ventilation rates, and inlet air temperatures on system performance. Stricter comfort constraints (PMV=-0.2 to 0.2) increase costs and emissions by 30.96 % and 37.5 % respectively, due to increased reliance on the natural gas boiler. Doubling the ventilation rate based on fresh outdoor air increases daily costs and emissions by 19 % and 22.6 % respectively. Conversely, utilizing a supplementary system to supply ventilation air at 25 °C significantly reduces costs and emissions by 26.2 % and 25.4 % respectively, and increases the solar fraction to 0.92. Compared to a conventional system powered solely by a natural gas boiler, the solar-powered system achieves substantial cost savings (45.9 %), reduced carbon emissions (52.5 %), and improved thermal comfort, highlighting the potential of this technology for sustainable building operations.