CHPWH Unpressurized Storage Design Optimization

Central heat pump water heater (CHPWH) systems are crucial for the efficient decarbonization of multifamily and commercial buildings. These systems can provide electrified, efficient hot water for both new and existing buildings while minimizing grid impact and energy costs with load shifting capabilities. However, additional production options and design solutions are necessary to overcome remaining barriers to widespread market adoption. This study will study unpressurized hot water storage designs that can reduce several of these adoption barriers and optimize unpressurized storage heat transfer.  Unpressurized storage solutions are being manufactured in California with commitments to several planned multifamily projects. There are several different available heat exchange designs: submerged passive heat exchange, external pumped plate heat exchange, booster pumping, and enhancements such as phase change materials or carbon nanotubes. The proposed study will computationally model the most likely design (closed loop, external pumped plate heat exchange) with and without phase change materials, assess the respective performance and benefits, and explore the market potential and implications of unpressurized storage. This will allow current and future manufacturers to refine their offerings towards maximal adoption and efficiency. This study will also pave the way for future field demonstrations at the anticipated early-adopter low-income multifamily buildings.