a b s t r a c tDistributed power and energy resources are now being used to meet the combined electric power, heating, and cooling demands of many buildings. The addition of on-site renewables and their accompanying intermittency and non-coincidence requires even greater dynamic performance from the distributed power and energy system. Load following generators, energy storage devices, and predictive energy management are increasingly important to achieve the simultaneous goals of increased efficiency, reduced emissions, and sustainable economics. This paper presents two optimization strategies for the dispatch of a multi-chiller cooling plant with cold-water thermal storage. The optimizations aim to reduce both costs and emissions while considering real operational constraints of a plant. The UC Irvine campus micro-grid operation between January 2009 and December 2013 serves as a case study for how improved utilization of energy storage can buffer demand transients, reduce costs and improve plant efficiency. A predictive control strategy which forecasts campus demands from weather predictions, optimizes the plant dispatch, and applies feedback control to modify the plant dispatch in real-time is compared to best-practices manual operation. The dispatch optimization and predictive control algorithms are shown to reduce annual utility bill costs by 12.0%, net energy costs by 3.61%, and improve energy efficiency by 1.56%.Ă 2014 Elsevier Ltd. All rights reserved.
IntroductionIncreasing concerns regarding electricity costs, energy reliability, and emissions are encouraging businesses and campuses to consider self-generation and district heating/cooling. Deployment of a combination of electric generators, energy storage devices, district heating/cooling, and electrical circuit infrastructure to meet the energy demands of several buildings comprises a micro-grid [1]. Micro-grids are typically connected to a regional electric utility network that provides supplemental electricity through a single high voltage interconnection. Regional utilities rely upon the temporal smoothing effect of aggregating thousands of dynamic consumer demands. At the micro-grid scale, i.e. 250 kW-50 MW, energy management similarly relies to some extent upon aggregation to temporally smooth demand, but primarily micro-grids must remain highly responsive to demand variations arising from building energy demands and energy supply dynamics caused by on-site renewable generators. High efficiency and low cost operation requires a continuous optimization and dispatch of resources and effective management of energy storage devices to balance power under all circumstances of dynamic load, dynamic generation, renewable intermittency or other perturbations [2]. Thermal energy storage (TES) technology, i.e. cold-water storage, ice, or molten salts, can assist to decouple demand from production. Use of any storage technologies introduces a time horizon to the dispatch optimization, which can be further complicated by physical and operational constraints. ...