Advanced design and control strategies to optimize a deep borehole field as long-term thermal storage
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Insinööritieteiden korkeakoulu | Master's thesis
Sustainable Energy in Buildings and Built Environment
Master's Programme in Advanced Energy Solutions (AAE)
AbstractLarge-scale external factors, such as climate change, global population growth and concentration have been providing building sector policy makers with forceful motivation. Past proposals included requirements both on building and system level: tightening energy performance, increasing integration of renewable sources, fossil-based CO2-emission decrease and further battery and storage utilization. Today, energy efficiency and recovery are core parts of the Scandinavian HVAC design practice; local thermal energy production and storage is getting more preferred, machine learning-based control with live energy analysis (Digital Twin) is gaining attention. The objectives of this thesis research are in line with the values of these policy changes. The thesis studies the operational and optimization possibilities of a newly constructed and serving deep borehole field, based on simulations using IDA ICE. Due to its volume the borehole field provided an excellent test bed, proven remaining balanced: without the danger of long-term cooling. Following the as-built field analysis, additional control mechanisms were developed and tested. Long-term thermal behavior (25 years span) was simulated with the intention to achieve willful thermal changes in field: balance and heat accumulation upon order. During the study, the role of parameter calibration unveiled its significance. The first calibration took place between the ground properties simulation and in-situ test results, in order the evaluate the most influential factors of the ground. The optimized parameters of such an energy source majorly influence its thermal output and physical processes. This example underlines the true implications of calibration: through repeated verification and validation, as the constant evaluation of simulation and measurement may become a tailored, real-time facility-wide control entity. The idea of the building Digital Twin is established on the real-time calibration. When it will be combined with external influencing factors (energy price, external weather) and with automated machine learning in a shared platform, the control mechanism may reach unseen high levels of building energy management. Another subject of the thesis studies, how ground-source energy storage are to become the main thermal sources of future small-scale, low-temperature “local” district heating networks, including approx. 7-10 buildings with similar load profiles. This novel type of network is based on building-network co-simulation, where the building demand delivery and the supplying network interactions are modeled, simulated and closely followed. Thermal energy trading between the buildings is desired, supply and long-term storage both guaranteed by a nearby borehole field. Conclusion of the thesis is that simulations shall mature as a major design tool in energy design, from the layout tables to real-time analysis and decision-making in long-term energy management.
SupervisorVirtanen, Markku J.
Thesis advisorVuolle, Mika
ground heat balance, thermal energy storage, borehole field, optimization, calibration, control strategies