Innovative combined optimization and modified maximum rectangle method for equipment sizing and operational strategy of an integrated system with cold thermal storage

Abstract

An innovative method is proposed here for optimum sizing of an integrated system and finding its operational strategy of equipment during a year. This system provided power, heating, and cooling loads of buildings. To decrease the electricity consumption and operating cost of compression cooling system, an ice thermal energy storage (ITES) and also absorption chiller included in the integrated system. Modified Maximum Rectangle Method (MRM M) is defined and combined with multi-objective optimization technique. Two objective functions were Relative Annual Benefit (RAB) and Exergy Efficiency (ηEx,tot). For a residential complex, MRMM and GA optimization methods obtained results in a more accurate and faster procedure. Analysis of results from OPT-MRMM showed that two 884 kW gas engines provided the highest exergy efficiency (46.54%), the maximum value of RAB (1.04 × 106 $/year), and the shortest payback period (3.64 years) for the optimized and selected integrated system in comparison with system specifications obtained by other studied methods. Results also showed that OPT-MRMM method provided the lowest waste heat, the lowest fuel consumption in backup boilers, the highest amount of selling electricity to the grid and the lowest amount of specific emission release in comparison with those for optimization or MRM method alone. Applying this method provided low amount of buying electricity from the grid as well.The results for our case study also showed that the annual electricity consumption of traditional Vapor Compression Refrigeration (VCR) reduced from 19.99 × 105 kWh/year to 16.18 × 105 kWh/year (3.81 × 105 kWh/year reduction i.e., 19%) when ITES added to the VCR equipment. Furthermore, shifting the electricity consumption from high tariff period (on-peak and mid-peak hours) to low tariff period (off-peak hours), reduced the annual electricity cost for 26.62%. Finally, the results showed 25%–32% reduction for annual electricity consumption of VCR-ITES in OPT-MRMM method in comparison with that for VCR alone.