Economic efficiency and carbon emissions in multi-energy systems with flexible buildings

Multi-energy systems (MES) offer an opportunity to leverage energy conversion processes and temporary energy storage mechanisms to reduce costs and emissions during operation of buildings, campuses, and cities. With increasing options for flexibility in demand-side resources, it is possible to temporarily defer thermal and electrical demand of (flexible) buildings without sacrificing comfort and convenience of its occupants, which can improve overall MES economic efficiency and reduce emissions. To that effect, this paper develops a linear optimization formulation of a MES with flexible (thermal and electric) building demands that capture nonlinearities in the efficiencies of energy conversion processes. The optimization formulation accounts for multiple time-steps to capture the (first-order) dynamics of large thermal building loads. The flexible buildings are parameterized, in part, based on historical data from a college campus in Vermont, USA. The idea of the MES model is to investigate the role that flexible building loads play in reducing costs and emissions for a small campus relative to that of a possible carbon tax. The operation of the MES is optimized to reduce costs based on representative seasons and carbon tax scenarios. Interestingly, it is found that when utilized optimally, flexible buildings can offer an effective method to improve economic efficiency while also reducing carbon emissions close to the levels that a carbon tax would realize, though without carbon price's large cost increases. That is, we present evidence that flexible buildings in Vermont may offer another route to achieve the emission goals close to that of a carbon tax policy.