If you have any further questions regarding our services or see potential for cooperation, please contact us by email or phone number given below:
© heatbeat engineering GmbH & heatbeat nrw GmbH 2017-
Dear Reader,
For the 47th issue of our heatbeat Research Newsletter, we take a closer look at the complex challenges of 5th generation district heating and cooling networks. We focus on an overview of the hydraulic design and the control strategies of these ambient temperature networks and summarize the findings of a recent published paper in this field.
The paper, "Development and Experimental Validation of a Hydraulic Design and Control Philosophies for 5th Generation District Heating and Cooling Networks" from Angelidis et al. presents an in-depth study focused on the development, experimental validation, and comparison of control strategies for 5th Generation District Heating and Cooling (5GDHC) systems. The research addresses the significant challenge of establishing effective control mechanisms that enable flow bidirectionality and energy synergies between heating and cooling within these networks.
The core design challenge of 5GDHC systems revolves around the management of an ambient temperature network that facilitates both heating and cooling. The paper proposes and experimentally validates two distinct control strategies.
This strategy involves controlling the return temperature in the grid, ensuring that it remains at a constant, predefined setpoint. It is designed to maintain a stable and predictable grid temperature, minimizing fluctuations that could negatively impact the system's operation.
The strategy demonstrated a slightly higher electrical consumption due to the mismatch between the evaporator and grid temperature difference, which required the internal pump of the Booster Heat Pump (BHP) to mix the return flow to maintain the desired temperature. This led to a Seasonal Coefficient of Performance (SCOP) of 3.84 over 20 hours of operation.
Unlike TGridFix, the TGridFloat strategy allows the grid temperature to float freely in response to the prosumers' power demands. This approach is intended to optimize system efficiency by allowing the grid temperature to vary naturally, thereby reducing the reliance on active temperature control.
TGridFloat exhibited better energy efficiency with a higher SCOP of 4.08. The reduced need for internal pumping led to lower electricity consumption. However, this strategy introduces unpredictability in the system's behavior, which could complicate the management of prosumer interactions and system stability over time.
The experimental validation was conducted using a small-scale 5GDHC setup at the Combined Smart Energy Systems (CoSES) laboratory at Technical University of Munich (TUM), which simulated real-world conditions with two prosumers—one demanding heating and the other cooling. The experiments ran for 20 hours, covering various scenarios including simultaneous heating and cooling demands, only heating, only cooling, and periods of no demand. The experimental setup leads to the following findings.
The experimental results confirmed that the proposed hydraulic design with decentralized pumps and a passive Balancing Unit (BU) is effective in maintaining system stability. The system successfully handled bidirectional flow without encountering control instabilities such as pump hunting, which is a common issue in decentralized pumping systems.
TGridFix provided better control over grid temperatures, which is advantageous for reducing the complexity of billing and maintaining predictable system performance. However, the energy efficiency was slightly compromised due to the need for additional pumping to maintain the fixed temperature difference.
Both control strategies showed that the proposed system design is robust, with no significant control issues observed during the experiments. The use of a passive BU and the control of decentralized pumps based on either temperature or flow rate contributed to the system's overall stability.
The paper concludes that while both TGridFix and TGridFloat are viable control strategies for 5GDHC systems, the choice between them should be based on the specific requirements of the system. TGridFix offers greater predictability and ease of implementation, particularly in billing and system-wide temperature management, but requires careful system design to avoid inefficiencies. On the other hand, TGridFloat provides greater flexibility and potentially higher efficiency but at the cost of increased system unpredictability.
The study emphasizes the importance of selecting a control strategy that aligns with the system's operational goals and highlights the need for further research, particularly in scaling up these strategies for larger, real-world applications where the challenges of prosumer interaction and system stability become more complex.
As always, we recommend reading the article in full. The article gives a good overview over the complexity of hydraulic design und control strategies in 5th generation district heating and cooling networks.
The next issue of our newsletter will be published on October 2, 2024.