Phase Change Material Applications in Multifamily Water Heating

While PCM TESS is gaining traction in HVAC and commercial sectors, residential waterheating applications remain nascent. High first costs, installer unfamiliarity, and lack ofstandardized data limit adoption. At the same time, California’s multifamily buildingsface complex challenges in transitioning to low-carbon domestic hot water (DHW)systems, especially in retrofit scenarios where space, cost, and distribution inefficiencieslimit electrification. This CalNEXT technology development study introduces a noveldesign: integrating Phase Change Material Thermal Energy Storage Systems (PCM TESS)into central DHW systems to enable more cost-effective and space-efficient central heatpump water heater (CHPWH) upgrades. This design reduces distribution losses, supportsload shifting, and minimizes the need for large central storage tanks by repurposingexisting recirculation infrastructure into a PCM charging loop. This report presentsinitial engineering designs, energy modeling results, and stakeholder feedback to informfuture lab testing and field demonstrations.The volume of central storage required for load shifting in typical CHPWH designs,combined with the need for swing tanks to manage recirculation loads, often createschallenges for buildings with space-constrained mechanical rooms. These componentscan increase first costs and reduce overall system performance. The proposeddistributed PCM system design addresses cost and system performance issues created bythe need for swing tanks and by existing mechanical room space constraints byrepurposing distribution and recirculation piping into a PCM charging loop. Thiseliminates the need for swing tanks and reduces central storage volume by up to 67%.Energy modeling of the PCM design shows a 26% reduction in heat loss from centralrecirculation systems and an 8% reduction in overall DHW load. For CHPWHapplications, load shifting enabled by PCM TESS can yield cost savings under time-of-use(TOU) rates, despite slightly higher energy use due to reduced central plant efficiency.These findings indicate that PCM TESS offers a viable pathway to expanding uptake andperformance of CHPWH systems in California’s multifamily buildings. Building on these findings, this study outlines a roadmap for further engineering development, fieldvalidation, and market adoption of PCM TESS