In a cluster of eight terraced houses, an energy system has been implemented, which should represent a smart integration of heat pumps. To coordinate the interaction of the components, model predictive controls are used. The simulation shows very good results for the predictive controls, but the results cannot be replicated in practice.
The cluster of eight terraced houses is located in Herzogenaurach (Germany) in the new district of Herzo Base and was built in 2017. The buildings were designed as “all-electric buildings”, which means that the core source of energy is electricity. The terraced houses share a central heat pump system of two modulating heat pumps (MHPs) of each 16 kWth, with a geothermal heat source as well as a battery system with a capacity of 40 kWhel. A PV-system (88 kWp) on the roofs delivers an annual surplus of energy. The supply of domestic hot water is decentralized in each terraced house by a domestic hot water-HP (Booster), which uses the heating buffer storage units as a heat source.
The standard operation in the energy system of the terraced houses is a PV-optimized control, which charges the thermal storage units up to a higher temperature level during PV generation. The increase in the 2nd monitoring year was relatively high at 13% and remained the same in the 3rd monitoring year. The simulation of the energy system with the PVC was implemented in TRNSYS and simulated with measured values from 2019. The simulation results show a higher load cover factor (LCF) of 68% and a supply cover factor (SCF) of 42%, which mainly results from a higher battery charge and discharge.
In order to introduce predictive control strategies, a simulation study was carried out in the first step. In the second step, the control strategies were implemented in real in the terraced houses. For the simulation of the control strategies, measured data of the energy system of the terraced houses for the year 2020 is used. For the use of the predictive controls, MPC and PC forecasting models are used to generate the thermal and electrical load forecast. The SPC uses the forecasting models as well as energy balancing to determine the heat pump operation and the state of charge of thermal storage units throughout the day.
The simulation of the control strategies shows that due to the large PV production, a very high PV self-consumption is already achieved in HC operation. Even though PVC and SPC have slightly higher energy consumption, the operating costs are less due to the use of PV. To test the control strategies in real operation, the Model Predictive Control (MPC) and a simplified predictive control (SPC) were implemented in the real energy system of the terraced houses. The process of MPC and SPC differs from PVC because an operating plan is created, which is then passed on to the heat pumps.
Christina Betzold and Arno Dentel, Germany
This text has been shortened by the HPC team
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