Experimental and modelled performance of a building-scale solar thermal system with seasonal storage water tank

Abstract

Building energy loads in cold climates may be largely offset with solar energy if seasonal thermal energy storage is employed. This article describes a full-scale experimental solar thermal system equipped with a 36 m3 buried water tank for seasonal storage. The solar thermal system provides space heating and domestic hot water to an energy-efficient two-storey research house in Ottawa, Canada. Long-term experiments on the system are described, which revealed key performance parameters for the system. Under-performing solar collectors were found to have the most detrimental effect on the system’s performance. Losses from the seasonal storage tank were found to exceed those predicted based on the nominally-rated insulation properties. Piping losses are shown to be non-negligible. A detailed simulation model of the building and solar thermal system was developed and validated with experimental data, and is used to demonstrate the potential performance of the solar thermal system with simple improvements to the experimental system. Results indicate the system can achieve a solar fraction of 100% for space heating loads (total load = 15 GJ) and 86% for domestic hot water loads (total load = 13 GJ). The seasonal storage tank achieves an annual energy storage efficiency of 42%. The performance results obtained in this article may serve as a benchmark for future research into the design, economics, optimization, and control of systems employing seasonal storage at the building scale.