Multifamily Domestic Hot Water Recirculation Survey

Temperature maintenance losses often account for around 30% of total thermal loads in centralized domestic hot water systems in multifamily buildings (but can be as high as 60%). Correction of these omnipresent recirculation inefficiencies in high-rise multifamily buildings has direct implications on central heat pump hot water system (CHPWH) design, energy usage, and sizing. A full understanding of the recirculation loads, their driving factors, corrective actions, and their relationship to building characteristics would benefit CHPWH market transformation. Currently, CHPWH design and sizing take a conservative approach in the absence of better information. Often they are generously oversized to ensure that both hot water demand and recirculation losses can be met. There are also limited rebate and program offerings in support of reducing hot water load in preparation for CHPWH retrofits. A full understanding of temperature maintenance losses and possible solutions would enable improvements to existing design tools, expand program offerings, reduce oversizing, energy consumption, associated installation costs, and potentially expand market offerings from systems relying on electric resistance swing tanks. Additionally, there may be an opportunity for updating or creating new efficiency portfolio measures for existing multifamily buildings. These can be standalone measures for existing buildings or provide added value to CHPWH retrofits. Existing measures covering pumping controls and insulation could be updated, market potential can be quantified justifying tailored marketing efforts for existing programs, and new measures could be possible for interventions such as rebalancing or crossover remediation. A field survey of recirculation systems in existing high-rise buildings will inform recommendations towards each of these ends. This study will gather field data from 15 multifamily buildings to quantify recirculation loads and their driving factors. Recirculation loads will be measured and correlated to as-built conditions such as pipe sizing, layout, balancing, insulation, and thermally isolating pipe supports. The impacts of each factor will be examined so that existing design tools can be adapted to accurately account for recirculation losses or recommend CHPWH configurations based on a simple set of building condition inputs. This data will be paramount to the expansion of design tools and sizing methodology for systems without swing tanks such as return-to-primary and multipass temperature maintenance configurations. These configurations are being tested in PG&E lab tests and could reduce installation costs, footprint, and energy consumption while expanding commercially available products. All of this would increase market transformation towards CHPWH systems and this field study would be a key step in that direction. In addition to CHPWH goals, the bases for existing measures in eTRM will be reviewed in case the survey data yields an opportunity for updates. The opportunities for balancing, insulation, pumping control, mixing valves, and crossover correction will be explored, with possible recommendations for new measure development.