Towards an integrated design of heat pump systems: Application of process intensification using two-stage optimization

Aiming for a sustainable building stock, air-source heat pump systems are a key technology. In residential application, heat pump systems typically consist of a heat pump, an auxiliary heater, two thermal storages (for space heating and domestic hot water), and a system controller. Compared to conventional technologies, the efficiency of a heat pump system is highly dependent on it's design, (component sizes, flowsheet, and refrigerant choice) and its operating conditions, particularly part load and temperature levels. While design strategies exist on different domains in the literature, there is no integrated strategy to optimally design heat pumps systems. In this work, we use process intensification to consider the heat pump system design and operation simultaneously. Formulating the intensification process leads to a two-stage MINLP optimization problem with multiple objectives: Costs and emissions. In the first stage, the design is optimized in an annual dynamic building performance simulation using a surrogate-based optimization procedure. Then, using the same dynamic simulation models, the system controller is optimized in the second stage using a Genetic Algorithm. Our results underline the necessity for integrated optimization process. The integrated process can decrease annualized costs up to 36% and emissions up to 51% compared to standard design procedures.