Using Solar Hot Water to Address Piping Heat Losses in Multifamily Buildings

Stacey Rothgeb, David Springer, Matt Seitzler, Christine Backman, Elizabeth Weitzel, Stacey Rothgeb (NREL Technical Monitor)

Research output: NRELSubcontract Report


Solar thermal water heating is most cost effective when applied to multifamily buildings and some states offer incentives or other inducements to install them. However, typical solar water heating designs do not allow the solar generated heat to be applied to recirculation losses, only to reduce the amount of gas or electric energy needed for hot water that is delivered to the fixtures. For good reasons, hot water that is recirculated through the building is returned to the water heater, not to the solar storage tank. The project described in this report investigated the effectiveness of using automatic valves to divert water that is normally returned through the recirculation piping to the gas or electric water heater instead to the solar storage tank. The valves can be controlled so that the flow is only diverted when the returning water is cooler than the water in the solar storage tank.
Original languageAmerican English
Number of pages44
StatePublished - 2015

Bibliographical note

Work performed by Alliance for Residential Building Innovation, Davis, California

NREL Publication Number

  • NREL/SR-5500-64662

Other Report Number

  • DOE/GO-102015-4716


  • arbi
  • Building America
  • domestic hot water (DHW)
  • multifamily
  • recirculation
  • residential
  • residential buildings
  • solar water heaters


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