The system functioned through four distinct modes, adapting to varying weather conditions. Mode 1 functioned exclusively on sunny days, utilizing solar collectors to heat the thermal storage tanks. On the other hand, Mode 2 relied entirely on the head pump during cloudy or rainy weather.
Mode 3 combined both, with solar collectors running during the day and the heat pump at night, and mode 4 optimized energy use by running the heat pump only during the day when solar energy was insufficient, avoiding nighttime operation.
The team observed the system for nine days and found that the sand-based thermal storage floor kept indoor temperatures stable between 63.3°F (17.4°C) at night and 68.4°F (20.2°C) during the day, even as outdoor temperatures ranged from -1.1°F (-18.4°C) to 54.1°F (12.3°C), averaging 22.1°F (-5.5°C).