Increasing the Energy Flexibility of Buildings controlled by Model Predictive Control

Abstract

The growth of renewable energy sources in the electricity grid and the electrification of heat generation in buildings using heat pumps increase the necessity of flexible consumers who can change their electric load. Operating the building in a flexible way means that the building’s load is adjusted, e.g. to an electricity price. Model Predictive Control (MPC) is seen as a key algorithm in building energy management systems to provide the requested flexibility. In most studies covering energy flexible buildings, the load shifting is achieved by an economic MPC that uses an objective function, which aims to minimize the building’s operating costs, assuming
a variable electricity tariff. However, the most economic operating point corresponds in the heating period to the lower limit and in the cooling period to the upper limit of the thermal comfort band. As a result, the available flexibility that a building can offer is limited. In this work, a novel formulation of the control law, aiming to increase the energy flexibility of buildings, is derived and evaluated. From the current operating point, the heat pump’s load for reaching the upper and lower comfort limit in the building is estimated. These two demand curves are used to determine a control signal that balances the trade-off between thermal comfort and operating costs whilst increasing the building’s available flexibility. The proposed control strategy is evaluated on lumped-element models of German single-family houses, which are equipped with heat pumps, using the day-ahead electricity price as an incentive. Different indicators (e.g. power shifting capability and flexibility factor) are evaluated showing increased flexibility but also
increased operating costs compared to classical economic MPC. Providing flexibility to the grid through demand response will require to operate the building at a point that is not cost-optimal. Higher operating costs on the building side would need future electricity contracts to include a flexibility refund in order to increase the building operator’s willingness to provide flexibility.