Quantification of deviations between grey-box and constant efficiency modeling and optimization of trigeneration systems using a data-driven RMSD indicator

Abstract

Optimization of energy systems witnessed the use of simple (constant efficiency) equipment models. Alternatively, grey-box (variable efficiency with part load) models were used to simulate a more real behavior of such systems. However, limited attention was given to deviations due to part load effect in planning, sizing, scheduling and sensitivity analyses. This paper provides a quantified methodology to reflect such deviations and to show to what extent simple model is valid. A detailed comparison between both models is developed by optimizing a trigeneration system to find its configuration, rated capacities, operating schedule and sensitivity to prices. A data-driven comparative criterion -root mean square deviation- is developed to compare models. It depends on deviations in combined efficiency that is based on four key performance energy, economy, environment and exergy indicators in addition to economic parameters being the decision attributes. Results show that the deviations in the combined efficiency; net present value; payback period; and internal rate of return are 40.45%; −71.26%; 30.37%; and −24.30% respectively, leading to an overall root mean square deviation of 45.35%. Simple model approach is valid to be used in the planning phase only. However, the grey-box model is the way forward for optimization of polygeneration systems.