Wax, Water, and Phase Change

Overview

As concerns about climate change and fossil fuel consumption grow, developing sustainable ways to store and use renewable energy has become increasingly important. Many home heating systems rely on electricity or fossil fuels, which can be costly and environmentally damaging. This project investigates a phase change material (PCM) thermal battery that uses water and paraffin wax as a potential method for storing solar thermal energy for residential space heating. By utilizing the latent heat of paraffin wax, thermal energy collected during sunny periods can be stored and later released to heat indoor spaces. To determine realistic design requirements, typical U.S. residential electric space-heating consumption was analyzed and converted into a daily heating demand of approximately 9 kilowatt-hours. If solar input is available for about 5 effective hours per day, the system would need to supply roughly 1.8 kilowatts of thermal power from a rooftop solar collector. Using a common estimate of 15 watts of thermal energy collected per square foot, the required collector area was calculated to be about 120 square feet. The daily heat storage requirement of 9 kilowatt-hours corresponds to 3.24 × 10⁷ joules of energy. With paraffin wax providing a latent heat of 184 joules per gram, approximately 176 kilograms of wax would be needed to store one full day of heating energy. A 5%-scale proof-of-concept system was also designed to test the feasibility of the concept. This scaled prototype targets 0.45 kilowatt-hours of storage, uses a collector area of 6 square feet, and requires about 8.8 kilograms of wax. The prototype’s fluid circulation system was automated using electrically actuated solenoid valves, which control the input and output loops that move heated water between the solar collector, the wax storage unit, and the radiator loop. Additionally, a small wooden architectural model was built to represent a simplified house section and illustrate how energy would move from a roof-mounted solar collector into the wax storage unit and ultimately into a room radiator. Together, these design calculations and physical models establish a foundation for future experimental prototypes that can test and refine the PCM thermal battery system.

Competition history

• CSEF 2026 Environmental Engineering (Track 2) (Senior Division) · Entry S-12-03

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