Subtopic 10c:Air-to-Water Heat Pump & Thermal Storage

Problem: Thermal energy storage (TES) solutions for HVAC&R applications typically require significant onsite customization and deliver inconsistent value for customers and utilities. TES solutions have the potential to deliver compelling value when compared with chemical batteries, but innovation is needed to drive reliable performance and yield consistently lower cost. Project Objective: Stow Energy (Stow) will build a scalable heat pump and thermal storage platform for American homes. The water-based platform will support heating, cooling, and hot water end uses by pairing commercially available air-to-water heat pumps and hydronic air handling units with a novel thermal storage device and a control center device. The water battery will be a rotomolded tank that uses water stored at atmospheric pressure to heat and cool water that passes through an immersed heat exchanger. The control center contains valves and plumbing specialties along with scheduling algorithms to optimize storage utilization and effectively serve the customer. The project will produce a highly standardized thermal storage solution that is a third the price of the leading lithium battery at the same scale. Phase 1 Actions: Stow will 1) test a range of heat exchanger materials and devices to optimize cost and performance in the thermal storage device, 2) test alternative materials and forms with potential to further drive down the cost of the thermal storage device insulated enclosure, 3) develop a control board that is optimized for contract manufacture, 4) test and validate integration of additional hydronic air handling unit types to support varied customer needs, and 5) develop predictive software algorithms to optimally dispatch the heat pump and water battery to minimize operating cost and carbon emissions. All technical work will be carried out using Stow’s on premise technical facilities, which include appropriate test equipment and rapid prototyping capabilities. Commercial Application & Other Benefits: Stow’s air-to-water heat pump and thermal storage technology enables low-cost deployment across the majority of existing detached single family homes with ducted central heating (>40m). The integrated TES platform boosts heat pump efficiency by 10-25% and increases heat pump available capacity by shifting heat pump operation to times of day with mild temperatures. Furthermore, the platform offers comparable round trip efficiency (85%-95%) to lithium batteries and suffers no degradation across a 20-year lifetime.