Report on multi-system control strategies for HMS

The optimization of the control strategy of the energy system of a building is crucial to increase the performance of the building and reduce the electrical energy withdrawn from the electrical grid. In this report the optimization of a control strategy for a residential building is described. The starting point is a rule-based control strategy that harmonizes the different technologies that compose the energy system.

The optimization consists in changing the setpoint of the thermal energy storage for the domestic hot water preparation and the dwellings’ setpoint for space heating and space cooling to reduce the electrical energy withdrawn from the grid and increase the self-sufficiency and self-consumption of the energy system. The optimization logic is based on a daily forecast of the energy consumption of the building and the daily forecast of PV system’s electricity generation. Both predictions are made according to the weather forecast (daily average temperature and daily global horizontal radiation). In order to provide more thermal inertia to the energy system and enhance flexibility, the thermal energy storage for domestic hot water preparation was tripled in size compared to the size suggested by technical standards. This allows to reduce the number of charging and discharging cycles within a day and increase the energy that can be stored.

The rule-based control logic that harmonizes the different technologies implemented in the energy system and the building, proved to be effective in guaranteeing sufficient levels of thermal comfort and environmental air quality. The control was tested with annual dynamic simulations performed in TRNSYS. The control was implemented on an energy system powered by a centralized heat pump and a photovoltaic system coupled with an electrical storage. The energy system was applied to two building archetypes, a low-rise multifamily house with 7 apartments, divided on three floors, and a high-rise multifamily house with 40 apartments divided on seven floors. The other technologies that were incorporated in the control are ceiling fans for air movement, venetian blinds for shading, decentralized mechanical ventilation units for air renewal and thermal energy storages.

These advanced control logics demonstrate that it is possible to shift the loads toward more favorable periods of the day by acting on few setpoint temperatures. The change of the setpoint to shift the loads increases the total electrical consumption because the COP of the heat pump gets lower. The load shifts have a positive impact on the system performance only when the additional consumption is covered by the PV system. In winter the self-consumption is high, meaning that the only way to further reduce the electricity withdrawn from the grid is to increase the size of the PV system. As in the reference building taken as example the roof and façade area capacity for PV installation is fully exploited, the additional PV should be installed somewhere else, which might be not feasible. During spring and autumn, the thermal load is low, and it could be possible to avoid any withdrawal from the grid by increasing the size of the battery by 20%. In summer a positive balance is reached. However, during some days in which there is a lower PV production there is still the need to withdraw electricity from the grid.

In high efficient buildings over 50% of the total electrical loads is due to appliances and lighting. For this reason, a sophisticated control strategy is not always sufficient to reach a positive balance throughout the year. Energy efficient appliances and an optimal selection of their working period are crucial to reach the positive energy balance. For this reason, the building’s users should be aware of when it is convenient to use the appliances and when it is not the case.

The developed control strategies will be readapted and implemented in the cloud-based house management system (HMS) of AdvanticSys. More details about will be given in deliverable D3.2.