Optimal energy management of grid-connected PV for HVAC cooling with ice thermal storage system

Abstract

Studies have shown that reducing cooling energy costs and increasing operational efficiency may be achieved by utilizing ice thermal energy storage (ITES) technology while maintaining the thermal requirements in space cooling facilities. Optimal control of the ITES system and integration of renewable energy (RE) sources such as PV and geothermal, depending on the availability of resources and application, can further improve the operation of HVAC's cooling systems and mitigate the increased energy cost required for ice formation and overall cooling energy.This study presented optimal switching control of the ice-build chiller for ITES charging and PV power source. Inputs to the model, simulations, and validations were implemented using the available data, which include the historical exogenous meteorological data, temperatures at the inlet and exit of the plant components, manufacturer's information, and readings from the plant's SCADA chosen for the case study.The main aim of the study was to develop an optimal control model that minimizes the energy consumption and cost in the Ice built chiller and other devices, such as pump fans in the HVAC system, by optimal charge and discharge of the ITES and supplementary utilization of the greener energy source PV source under the time of use (ToU) tariff and desired cooling load demand. The case study for a healthcare building was considered in implementing the model.Simulations were implemented in the MATLAB optimization toolbox with the Solving Constrained Integer Programs (SCIP) solver, which was chosen to address mixed integer programming (MIP) problems. It incorporates algorithms like a branch and cut conflict analysis and pre-solving techniques to handle intricate optimization problems involving continuous and discrete decision variables.The optimal switching control model yields approximately 33 % of energy cost savings during the summer months that involve using the HVAC with ITES compared to the current system control (baseline). Additionally, the ITES temperature remained below 0 °C to maintain thermal requirements as an operation constraint. The inclusion of PV and battery options as a source of power to the pumps accounted for 10–15 % of the overall energy usage of the system. Optimal control of the system to utilize the stored energy during peak pricing and high demand periods eliminated the extreme dependence on grid energy in some instances. Despite the additional capital required for the controller, solar PV, and batteries installation, the study projects a return on investment within two years, with a 20-year lifetime energy cost savings estimate of 35 % if inflation and annual electricity price increases are estimated at 5 % and 10 %, respectively.