Millions of rural households worldwide still rely on outdated heating methods, burning wood and coal to keep warm. This not only harms the environment but also poses serious health risks. In China alone, nearly 400 million tons of coal are used annually for winter heating, with almost half burned in inefficient small stoves.
In response to this challenge, researchers from Zhongyuan University of Technology and Dalian University of Technology have introduced an innovative heating system that integrates a solar-air source heat pump (SASHP) with a sand-based thermal storage floor (STSF). This pioneering approach offers an efficient and sustainable way to keep rural homes warm while reducing dependence on traditional fuels.
The experimental system was installed in a rural single-family home in Chifeng, Inner Mongolia. Led by Dr. Pengli Yuan, the research team designed a heating setup that includes a solar-thermal collector, a thermal storage tank, an air source heat pump, a sand-based thermal storage floor embedded with pipes in a 200-millimeter layer of sand, and water pumps to circulate heat efficiently.
The sand-filled floor plays a crucial role in the system’s effectiveness. When solar radiation is sufficient, the sand absorbs and retains a substantial amount of heat, gradually releasing it into the room. This stored heat continues warming the indoor space even at night or during cloudy periods, extending the duration of solar heating. Researchers highlight that this approach not only enhances solar energy utilization but also significantly reduces the operational time of the heat pump in cold and humid conditions, leading to improved efficiency.
The SASHP-STSF heating system adapts to different weather conditions through four distinct modes. On sunny days, the solar collectors heat the thermal storage tank, supplying warmth without relying on the heat pump. During cloudy or rainy weather, the system shifts to operating solely on the heat pump. A combined approach is used in mixed conditions, where the solar collectors function during the day while the heat pump supplements heating at night if necessary. An optimized mode further improves efficiency by running the heat pump only during the day when solar energy is insufficient, reducing nighttime electricity consumption.
During a nine-day trial, researchers observed that the sand-based floor effectively maintained indoor temperatures between 63.3°F (17.4°C) at night and 68.4°F (20.2°C) during the day, even as outdoor temperatures fluctuated between -1.1°F (-18.4°C) and 54.1°F (12.3°C). The system demonstrated a coefficient of performance (COP) of 2.6 and a solar fraction (SF) of 50.9%, proving its efficiency as a practical heating solution for rural areas.
Using TRNSYS, a widely used simulation tool for energy systems, the researchers modeled the system’s performance over a six-month heating period. They found that the optimized mode outperformed the combined approach, achieving a coefficient of performance of 4.6 and a solar fraction of 77.9%. These improvements translated into a 15.9% increase in efficiency and a 20.3% boost in solar energy utilization while using 405.2 kWh less energy.
However, cost-effectiveness depends on local electricity pricing policies. Without peak-valley pricing, the optimized mode reduces costs by 28% compared to the combined approach. However, under peak-valley pricing schemes, the cost difference narrows, with the optimized mode costing only 2.6% more. Researchers emphasize that adjusting the operational mode based on local electricity pricing can minimize expenses. They concluded that while the combined approach remains the most economical option for rural households under peak-valley pricing, the optimized mode offers a more sustainable long-term solution for energy conservation and emission reduction from a national policy perspective.
This innovative system presents a promising alternative to traditional heating methods, offering an eco-friendly, cost-effective, and scalable solution for rural communities. With further refinements and government support, sand-based thermal storage technology could play a crucial role in reducing carbon emissions and transitioning rural households toward cleaner energy sources.
The study has been published in the journal Case Studies in Thermal Engineering.
