Recovery Act - Phase Change Slurries for Residential Thermal Energy Storage

Currently, refrigeration and air conditioning in buildings account for approximately 8.5 quads of U.S. primary energy conception of which the primary consumption occurs with the refrigeration compressor. To alleviate this demand, thermal energy storage (TES) systems can be utilized to shift thermal loads to off-peak times. Cost savings can result if the pumping cost associated with the TES system is less than the difference of the compressor cost during peak times and off peak times. To assist in reducing energy demands within residential buildings, Mainstream proposes using an active TES based upon a phase change slurry (PCS) comprised of a water-glycol carrier and micro-encapsulated phase change material (PCM). This active system which can be integrated with the heating-ventilation-air conditioning (HVAC) system as well as directly coupled to the air stream within the building will reduce peak demand with a minimal energy penalty. For a 200-gallon capacity TES system, a 40% loading of the micro-encapsulated PCM will offer a thermal capacitance of 50 MJ. In practice, the thermal capacity will be greater than this value as the carrier fluid will possess additional capacitance as sensible heat storage. The conservative estimate translates to approximately 2.3 kW for 6 hours or 3.5 kW for 4 hours. TES systems, primarily based upon chilled water or ice-storage, have been utilized as a cost reduction method for industrial and large commercial sites for several decades and for the residential market in select trials. Each system has unique advantages and disadvantages. Chilled water systems are simple to implement but only offer moderate thermal capacitance per unit weight. Ice-storage systems offer high thermal capacitance but result in a greater system complexity. The proposed technology would have the operational simplicity of chilled water system while maintaining high thermal capacitance similar to ice-storage. The proposed TES would be integrated within the building