Advanced modeling and energy-saving-oriented assessment of control strategies for air-cooled chillers in space cooling applications

Chillers are reference technologies to meet the demand for space cooling in the tertiary and commercial sectors. Meantime, being power-to-cold technologies, they could increase the flexibility of these buildings in those contexts of a high share of electricity from renewable energy sources through new control strategies. To reliably assess the achievable energy savings in these novel applications, models capable of simulating not only the steady-state operation but also the dynamic response are required. However, the operation of these systems is usually evaluated through highly simplified models, also omitting controls. To fill this gap, this paper proposes an integrated thermodynamic and control modeling for an air-cooled chiller, accounting for usual and innovative control strategies. To show the capabilities of the model, an air-cooled chiller serving an office in the Mediterranean area is assumed. Both a variable-speed chiller and a constant-speed chiller with sequential control for compressors are simulated. Results show that for a variable-speed chiller, the set point for the supplied cold water is met, and the thermal inertia of the hydronic loop affects the reaching of the steady-state operation. In the case of a constant-speed chiller with sequential control, the number of "ON-OFF" cycles for each compressor is monitored and the minimum inertia of the hydronic loop for the safe operation of compressors is found. The analysis reveals that a variable temperature setpoint for the supplied water allows for a percentage increase in the energy performance between 10.8% and 60.3%. The proposed model enables the analysis of innovative controls aimed at improving energy savings and increasing building flexibility.