Air Dynamics Novel Low-Cost Thermal Energy Storage System for Buildings

Air Dynamic, in collaboration with its academic partner, University of Maryland (UMD), propose to develop a novel cross-media thermal energy storage system (CMTES) that promises high volume energy capacity (70 kWh/m3), high effective thermal conductivity (>15W/mK), low cost ($14/kWhthermal), and high corrosion resistance for thermal energy storage system (TES). The TES will use Sodium Sulfate based salt hydrates as the phase change materials (PCMs) due to its high volume energy capacity (100 kWh/m3), low melting temperature (~30oC), and low cost ($0.11/kg). The CMTES will be used for time-shifting on-peak load to off-peak load in residential and commercial buildings. The technology is leveraged under UMD’s previously funded ARPA-E project on development of inexpensive, 3D printed heat exchangers that are highly effective, and use a patented cross-media heat exchanger concept that substantially reduces thermal resistance between the hot and cold sides of the HX. As part of phase I of the proposed project we will develop initial technology demonstration unit and demonstrate PCM integration and operation into an additively manufactured CMTES. The CMTES consists of chambers filled with phase change material (PCM) and channels for the working heat transfer fluid. The chambers and channels are separated via walls made of polymers, while metallic wires extend continuously through the cambers and channels to provide a heat transfer route between the PCM and the working fluid. The polymer matrix act only as the fluid channel and pressure containment wall, whereas the metallic wires are responsible for transferring heat between the PCM and the working fluid. This arrangement eliminates the polymer channel wall thermal resistance, resulting in a TES with high thermal conductivity (20x compared to state-of-the-art). Moreover, the use of polymer wall significantly improves the corrosion resistance of the TES. The CMTES is fabricated using a custom-designed fused deposition modeling (FDM) 3D printer. Our unique AM machine consists of multi-nozzle head that lay down polymer and array of metallic fibers simultaneously, improving the printing speed by 100-200 times over that of conventional 3D printers, which significantly reduces the fabrication cost and allows for fabrication of large-scale CMTESs. Our analysis shows that a 10 ton rooftop chiller unit can be replace with a smaller 5 ton unit chiller and a 5 ton CMTES, with immediate payback period. The CMTES will be used to offset 50% of cooling load for four hours of peak demand. Based on the time of use, with electricity rate of $0.08/kWh off-peak, $0.35/kWh during peak and $0.56/kWh during critical peak demand, implementation of TES will reduce the electricity bill by 40% to about $210/ton/year, making it very attractive for the end user.