Sizing procedure of low-enthalpy district heating and cooling heat pump plants: A case study of the Balearic Islands university campus

• The methodology is used to size heat pump for low-enthalpy district heating and cooling networks. • It prevents oversizing compared to DIN EN 15450 standard. • Decentralized and centralized units are balanced to minimize ON/OFF cycling. • Thermal demand fluctuations and outdoor temperatures are integrated in the design. This study introduces a sizing procedure of low-enthalpy district heating and cooling heat pump plants to improve operational efficiency and prevent oversizing. The approach integrates thermal demand simulations with EnergyPlus™, a statistical analysis of thermal loads, and a Mixed-Integer Linear Programming optimization model. The methodology follows a two-step process: first, it decides the size and configuration of decentralized heat pump plants and then determines the capacity of the centralized plant among different predefined alternatives based on a statistical analysis of the thermal loads, considering existing units already installed in the buildings. Applied to the University of the Balearic Islands university campus, where a new district heating and cooling network will serve eight buildings, this methodology significantly reduces unmet thermal demand while ensuring that heat pumps operate within their compressor operational range for longer periods. Compared to traditional peak-load-based sizing, the proposed approach lowers installed capacity by 18.79% when considering the peak cooling demand of the entire network and 28.47% when analyzing each building individually. The findings underscore the importance of integrating demand fluctuations and outdoor temperature variations into system design. By balancing decentralized heat pump units with a centralized plant, this framework offers a scalable, energy-efficient solution for next-generation DHC networks that enhance sustainability while reducing the total installed capacity of the heat pumps.