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

Abstract

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 36 m 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 (>30 m 3 ). However, a moderately lower solar fraction of 70-80% may be obtained even with significantly smaller tanks (<10 m 3 ), provided an "oversized" solar thermal array is utilized, which may come at a significantly lower investment cost.Back in a simpler time, I sent Ian (or then, Prof. Beausoleil-Morrison) an email about grad school. He mentioned a little project with a water tank -sounded simple enough! Little did I know the next several years would be one of the most difficult and rewarding periods of my life. Ian, thank you for providing me with this opportunity, and for your patience, guidance and wisdom over these years.I'm lucky to work alongside an incredible group of people within SBES and the BPRC. Thanks to my lab mates, colleagues and friends for the coffee breaks, karaoke nights and games of Catan.

Experimental Results of a Solar Thermal System with Sensible Storage in a Single Family Residential House

“…Nonetheless, previous experiments and simulations at CHEeR showed that such glazing levels can still cause winter overheating. A 4.38% ratio of south-facing glazing to conditioned floor area was used during this experiment which was significantly lower than the 8% used in Meister's experiment [7]. The shading configuration for this experiment is detailed in Table 3.2.…”

“…However, these experiments faced challenges due to faulty solar collectors and issues with the data acquisition system which resulted in an incomplete data set. Despite these setbacks, CHEeR managed to achieve a solar fraction of 68% [7].…”

“…Curtis Meister (2015Meister ( -2022 [21]: Meister's work at CHEeR house focused on the solar thermal combisystem coupled with a seasonal water-based thermal storage. Despite challenges with the solar collectors and data acquisition system, the house achieved a solar fraction of 68%.…”

“…See Table 3.1 for the insulation characteristics of CHEeR. More detail regarding the thermal performance characteristics of building envelope components are available at [7]. The second floor of CHEeR is topped by a vented, unconditioned attic.…”

“…Meister [7] suggested that the supply water temperature to the radiant floor loop could be reduced without compromising CHEeR's heating performance. Consequently, when the STES neared depletion on January 18th, 2022 the supply water setpoint of the heating system was lowered to 28°C.…”