Performance analysis of an advanced variable configuration solar cooling plant with an MPC controller. Part A: Model and validation

The design phase of a solar heating and cooling plant typically requires detailed data on user demand and weather conditions and the adopted plant configuration is strongly dependent from both of them. Since there are many uncertainties about them, many plants, correctly sized, showed a poor performance in terms of primary energy saving. In this work, the idea of a “variable configuration” solar cooling plant, which can self-tuning its own layout and adapts to different weather and user conditions and can guarantee the maximum primary energy saving, was investigated. The proposed solution tries to include part of the critical problems faced during design phase into the “control problem” solved every time during plant operation in order to guarantee a better primary energy saving independently from unpredictable external conditions. In this way, the “control problem” includes the temperature setpoints, variable flow rate setpoints, storage bypasses, and all the machine range operations. The results obtained by a parametric analysis done with a numeric model specifically developed allowed to evaluate the effective benefits of a variable configuration plant coupled with an MPC controller able to compensate for possible low performance due to wrong design procedure or wrong weather forecast. A maximum performance increment of ∼30% was observed in terms of PER.