Activation strategies for decentralized booster heat pumps based on dynamic pricing models

Achieving carbon-neutral energy supplies in collective heating systems is increasingly feasible through the use of renewable energy sources and optimized heating capacities. Within apartment buildings, a combined heat distribution circuit (CHDC) that supplies both domestic hot water (DHW) and space heating through a single pipe offers significant potential.

Traditional CHDCs require high distribution temperatures to deliver DHW, leading to inefficiencies. Lowering distribution temperatures enhances system efficiency, but might require decentralized booster heat pumps (BHPs) in each dwelling for DHW production. Currently, these BHPs recharge local DHW storage tanks based on temperature sensors, ignoring electricity prices [1]. As time-variable electricity pricing models are on the rise to balance production and demand in the electricity grid, there is an opportunity to control BHPs based on such variable price signals to minimize operational costs.

Demand-side management strategies have been focusing on day-ahead electricity market interaction. Thermal storage can be used to shift electricity consumption and thereby reduce energy costs. However, the most optimal moments depend on future prices, current state-of-charge, and future DHW demand in the respective dwelling. This research contributes to the literature by finding the optimal trade-off between energy cost and the extra heat losses of storage tanks during demand-side management.

This research aims to develop and evaluate various price-based control strategies for the optimal activation scheme of decentralized BHPs in CHDCs. These activation schemes decide when to recharge DHW storage tanks with BHPs based on future electricity prices. The objective is to minimize energy costs while maintaining thermal comfort. The methodology includes creating predefined recharging time slots during the lowest electricity price of the day-ahead market prices and comfort-based approaches that incentivize BHPs to recharge during low prices or restrict recharging during high prices. A detailed simulation model is developed, incorporating thermal dynamics, electricity price fluctuations, and various DHW consumption patterns.

Simulation results show that increasing the central distribution temperature during BHP activation offers no cost savings, as the central geothermal heat pump is decisive for overall economic efficiency. While price-based (de)activation strategies with constant supply temperature can reduce operational costs, they may slightly increase DHW discomfort.To properly benefit from low-price periods, BHPs should have larger thermal heating power. Future work should incorporate demand forecasting and include potential tariff structures for space cooling to improve system efficiency and cost-effectiveness.