Solar Water-Heater Proposals: Compare Active and Passive Systems

In DOE’s December 2003 guide, active systems pump water or nonfreezing fluid through collectors. Direct circulation pumps household water where freezing is rare; indirect circulation uses nonfreezing fluid and a heat exchanger.

Its passive-direct systems use no pumps or electricity; the guide cautions against their use where temperatures often fall below freezing. The simplified diagram labels solar storage and a conventional backup heater. DOE/NREL guide

Compare each proposal’s circulation path, pump, fluid, heat exchanger, storage and backup details. Ask the proposer to resolve omissions against current product documentation and site/climate conditions; this dated guide does not establish suitability or current installation requirements.