Combined cooling, heat and power for commercial buildings: Optimization for hydrogen-methane blend fuels

Abstract

Considering the rapid pace of global warming, it is crucial to decarbonize our energy supply to meet both electric power and thermal energy demands. This study evaluates the application of a combined cooling, heat, and power system for commercial applications in a maritime temperate climate to assess the feasibility of meeting thermal and electrical demand with medium-size commercial generators fueled with blends of hydrogen and natural gas. Demand load data analysis has been conducted using open-source datasets to identify building categories with representative thermal and electrical demands. A large hospital was chosen for a representative case study to define system component capacity and operation optimization to minimize estimated costs and greenhouse gas emissions. Along with the generator, the combined cooling, heat, and power system included thermal energy storage and an absorption cooler, supplemented with conventional boiler and an electric (vapor compression) cooling system. The optimized system was compared to a conventional combination of grid electrical supply for power; cooling from an electrical chiller; and heat load from a natural gas boiler. A hierarchical clustering algorithm was employed to identify five representative days to cover the entire year while keeping the optimization tractable. The system was sized using nested optimization, where operation over the year was optimized for a given system component sizing, then the sizing was adjusted, and the operation re-optimized in an iterative process. This ensured that the final system specification was optimized for both component size (capacity) and operation. The results show that a combined cooling, heat, and power system can provide economic and greenhouse gas emissions benefits for electricity grids with marginal CO2 intensities greater than 230–260 g/kWh. Adding up to 50% hydrogen to the natural gas can reduce this break-even intensity by up to 12%. Net cost savings on the order of 5% can also be achieved at the break-even greenhouse gases grid intensity. Depending on the grid CO2 intensity and fuel composition, combined cooling, heat, and power can save more than 14% compared to the conventional system in 20 years.