Researchers from University of Alaska Anchorage revealed long-term monitoring results from a thermal energy storage system located in a very cold place with a long winter season
Increasing global warming and climate change have led to growing focus on use of renewable energy. Several studies are focused on active and passive solar types of solar thermal storages for use in moderate temperature zones. However, research in application of solar thermal storage in colder regions such as Alaska is rare. According to American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook—HVAC Applications, published in 2003, active solar thermal systems are not appropriate in regions with extended duration of very cold temperatures. Now, a team of researchers from University of Alaska Anchorage revealed results of the long-term monitoring of an experimental house with thermal storage. The team offered method to determine the thermal properties of the thermal storage and compared results of experimental measurements to numerical results.
A 2-story house was built in the city of Palmer, Alaska for this study and was designed to be Net Zero Energy (NZE). Electricity is supplied from the utility grid at times of low solar production and is fed to the utility grid at times of high solar production to achieve NZE status. The thermal storage contained pit run, fine sand, and concrete. A propylene glycol-water solution was used as a thermal working fluid. Glycol was added to water to prevent freezing of the lines and potentially rupturing the tubes. The team used TRNSYS software for numerical simulation. Average temperatures were used to model the thermal storage losses and the loss coefficients of each side were taken as a ratio of that particular side to that of the whole thermal storage. The team recorded glycol-water mixture return and supply temperatures to the thermal storage at 1-minute intervals with Resistive Temperature Detectors (RTD) sensor.
The team found that seasonal solar thermal storages are feasible options in reducing the cost of energy in a region with extended freezing periods. The team also presented a detailed method to determine the thermal properties of the thermal storage. The heating load of the garage was reduced by 41.5% under the given climatic conditions due to the use of thermal storage. Moreover, thermal storage systems made of readily available materials such as sand and pit-run can offer a cost-effective approach to store thermal energy in a region with extended freezing periods. The research was published in the journal MDPI Energies on May 13, 2019.