Seasonal Thermal Energy Storage in Buried Water Tanks for Single Detached Houses

Seasonal thermal energy storage (STES) could allow solar energy to offset the majority of building energy loads in cold climates. This thesis outlines one of the first long-term, full-scale experimental studies on seasonal storage at the single-detached home scale. A solar thermal system couples a large evacuated tube solar array to both short term thermal storage tanks and a 36m^3 buried water tank used for seasonal storage. Solar heat stored in these water tanks provides space heating (SH) and domestic hot water (DHW) to an energy-efficient two-storey research house in Ottawa, Canada. Long term experiments are described, including a one-year cycle of the system and long term heat loss monitoring. Results show that the as-built system can meet the majority of the building's SH and DHW loads, achieving a solar fraction of 68%. However, experiments revealed several areas of underperformance. Most prominently, faulty solar collectors limited the system's potential. To assess the true potential of the system, detailed energy models were developed and validated against experimental data. Simulated free of faults and underperforming components, the system has a predicted solar fraction of over 90%. Building simulation is further used to explore improved control and sizing of STES systems for single-detached homes. Control methods and decisions such as variable speed pumping, radiant floor supply temperature modulation, and storage setpoints are explored, among others. In regard to sizing, for the house under study, it is shown that solar fractions over 90% require relatively large (and potentially costly) STES tanks (30m^3). However, a moderately lower solar fraction of 70-80% may be obtained even with significantly smaller tanks (10m^3), provided an "oversized" solar thermal array is utilized, which may come at a significantly lower investment cost.